Assistance to Fisheries Research Institute - Report Prepared by National Consultant for Shrimp Culture













Table of Contents


ASSISTANCE TO FISHERIES RESEARCH INSTITUTE,
MYMENSIMGH BGD/89/012

BGD/89/012

Prepared by

Nani Gopal Das

FISHERIES RESEARCH INSTITUTE, MYMENSINGH GOVERNMENT OF THE PEOPLE'S REPUBLIC OF BANGLADESH

UNITED NATIONS DEVELOPMENT PROGRAMME

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS

This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.


Table of Contents


ACKNOWLEDGEMENT

1. INTRODUCTION

1.1. Terms of Reference
1.2 Activities

1.2.1. Present Status

2. GHER FISHERIES

2.1. Major Gaps
2.2. Gher Management

3. SEED PRODUCTION OF MULLET

4. EXTENSION PAMPHLET

4.1 Polyculture of P. monodon and mullet in the Brackishwater ponds
4.2. Semi-intensive culture system of P. monodon

5. KEYS FOR IDENTIFICATION OF POST-LARVAL SHRIMP AND PLANKTON

6. RECOMMENDATIONS

7. REFERENCES

8. ANNEXURE

8.1 Keys for identification of post-larval shrimps and plankton


ACKNOWLEDGEMENT

The consultant expresses his deep and sincere gratitude to Dr. V.R.P. Sinha, Senior Specialist and Team Leader of the Project for his kind cooperation, valuable suggestions and overall guidance throughout the consultancy period.

The consultant wishes to express his sincere gratitude to Dr. M.A. Mazid, Director of FRI and also National Project Director for his sincere cooperation, valuable suggestions and guidance in carrying out the consultancy successfully.

Sincere thanks and gratitude are also extended to the CSO of the Brackishwater Station of FRI and other scientists for their cooperation.

1. INTRODUCTION


1.1. Terms of Reference
1.2 Activities


The Government of the People's Republic of Bangladesh has undertaken FAO/UNDP Project BGD/89/012: Assistance to Fisheries Research Institute (FRI) to assist the institution to make it a centre of excellence in fisheries research. In order to strengthen the brackishwater shrimp culture development the consultant was assigned to the project for the period of 2 months 10 days from 26 July to October 4, 1994 with the following terms of reference.

1.1. Terms of Reference

- Assist the counter-part scientists in undertaking extensive and semi-intensive culture of shrimp in monoculture and also with fish;

- Prepare the extension pamphlet for cost effective and environment compatible shrimp culture technology;

- Assist in such other activities which would be required from time to time for the successful implementation of the project on "Assistance to the Fisheries Research Institute";

- Prepare the terminal report of the work done.

1.2 Activities


1.2.1. Present Status


1.2.1. Present Status

About 120,000 ha area is presently under shrimp culture which was only 25,000 - 30,000 ha in the year 1980. However, about 0.2 million ha of coastal tidal lands has potential for shrimp and fish culture (MPO, 1986).

Shrimp farming in the country is by and large still traditional and the following four types of culture systems are practised:

- Salt, shrimp and fish culture;
- Shrimp and fish culture;
- Gher culture
- Monoculture of Penaeus monodon.

In Chakaria and Cox's Bazar region salt is normally produced from January - March. After that shrimp and fish are cultured in the same field. In Khulna region salt is not produced normally and the farmers culture only shrimp and fish (particularly mullet).

'Gher' culture is practised specially in Khulna region. This is the most traditional method which is 'trapping and holding' operation of shrimp and fish seed in paddy field.

Monoculture of. P. monodon is a recent development where systematic farming of shrimp is undertaken particularly in Cox's Bazar and Khulna area.

The seed requirement for all the above systems of culture is met from natural collection or trapping of wild fry. Post-larvae of penaeid shrimp are available round the year with peak during pre-monsoon and monsoon months in estuaries and near shore waters. Large number of other commercially important penaeid shrimp, caridean shrimp(prawn), fin-fish larvae and zooplankton migrate to the coastal nursery ground along with P. monodon postlarvae. It was estimated that while collecting seed of each monodon fry, 22 individuals of shrimp fry other than monodon, 30 individuals of fish fry and 47 individuals of other zooplankton are killed (Das et al., 1992). Thus, indiscriminate killing of other aquatic organisms during collection of P. monodon is rampant (FRI, 1991 and BOBP, 1993). Further, mortality of shrimp seed (P. monodon) occurs during their transportation and immediately after stocking. All these are serious drain on estuarine biodiversity which will have great adverse consequence on natural productivity.

Due to insufficient and erratic supply of wild fry, systematic shrimp culture suffers. The greater Khulna region which has about 75% of the total potential area for shrimp culture, badly suffers due to shortage of seed. There is no hatchery yet available in the region and farmers get supply of seed partially from local collectors or from the suppliers of Cox's Bazar region.

Recently one private hatchery "Pioneer Hatchery Ltd." which has come up successfully and producing about 25 million PLs in one cycle at Cox's Bazar.

Shrimp farms are primarily located in Bagerhat (29%), Satkhira (19%), Khulna (21%) and Cox's Bazar (31%). In addition, some small areas are also available in Keshabpur Thana of Jessore, Kalapara Thana of Patuakhali, and Anwara and Banskhali Thanas of Chittagong. But more than 70% of the total cultured area is located in greater Khulna region mostly as 'gher', varying in size from 0.2 ha to over 400 ha, averaging 28 ha (MPO, 1986).

The water control systems are normally not based on local hydrography, and the farms are not having proper inlet screen and thus predators enter. However, some farmers have started certain improvement in cultural practices. They exchange tidal water through fine meshed screens to prevent entry of predator and stock the ponds with post-larvae, and juveniles of P. monodon. They also use lime and fertilizers to maintain and to increase the natural fertility. Sometimes, they provide supplementary feed containing rice and wheat bran, mustard oil cake, fish meal, trash fish etc. The improved management increase the production to the range of 200-500 kg/ha/crop, compared to 80-120 kg/ha/crop in traditional system.

In Cox's Bazar and some in Khulna region, farmers have started semi-intensive culture of shrimp recently. They stock post-larvae (12-15 mm) at a very high density (15-30 m2) and feed them with artificial pellet diet. Some aerate their ponds. The production in semi-intensive culture has increased to 2500 kg/ha/crop.

2. GHER FISHERIES


2.1. Major Gaps
2.2. Gher Management


The gher fisheries is normally practised in the paddy field where paddy is cultivated alternately with shrimp. It is essential to increase the production and productivity of "gher" fisheries because its contribution is to the tune of 75% of the total production in the country.

It is most essential to focus the immediate attention of the scientists of the Brackishwater Station of FRI to help improve the gher management on the scientific basis. Therefore, the consultant initiated extensive survey of gher fisheries along with the counterpart scientists to find out the gaps in the gher management and to evolve better management practices.

The facilities of initiating the experiment at this station are not available at present. And the strategy of the institute is also to undertake such work as much as possible in the farmers gher.

The most stricking feature was that along with shrimp considerable amount of mullet were also harvested from gher. This indicated promising possibility of shrimp and mullet culture together.

The FRI scientists were assisted to understand many aspects of gher fisheries. Interview of the farmers were taken and in-depth discussion on the management issues were held. Major physico-chemical characteristics of the soil and water were monitored from some selected spots of various sized ghers by the consultant in collaboration with the FRI scientists to assess productivity status.

Water quality parameters

Depth

0.5-1.5 m

pH

6-7.5

Temperature

28-32°C

Salinity

2-5 ppt

DO

2-6 ppm

Turbidity

15-35 cm

NH3

0.1-0.5 mg/L

Soil quality


Soil pH

5.0-7.5

Stocking and production

Stocking density

5000-20,000/ha

Production level

200-1000 Kg/ha

Although it was a harvesting season yet physico-chemical parameters of water indicate the suitability for shrimp production. However, if water and soil quality are upgraded through proper fertilization, high production of shrimp can be expected from the existing gher.

The following gaps have been identified and thoroughly discussed for implementation of the programme.

2.1. Major Gaps

2.1.1 Gher preparation

2.1.1.1 Irregular size and uneven bottom:

It was found that most of the ghers are of irregular size with uneven bottom. Some are too small, even less than 0.2 ha while others are too large, even more than 400 ha. Such size creates problem in proper management. The farmers got convinced of the proper size, which should be in the range of 2-5 ha with an average depth of 1 m.

Gher needs to be prepared properly to eliminate the pests and predators. Farmers were suggested that after harvesting and drying the pond, the bottom needs ploughing.

2.1.1.2 Improper liming

Farmers do not apply lime in the 'gher'. They were appraised of the role of lime in neutralizing the acidity of soil, creating buffering action to prevent marked diurnal changes from acidic to alkaline conditions of the water precipitating colloidal matter etc. and its role in making the aquatic ecosystem hygienic.

The guideline for lime dose was given to the farmers as shown below:

Soil pH

Lime (Kg/ha)

4.0-4.5

1500

4.6-5.0

1250

5.1-5.5

1000

5.6-6.0

750

2.1.1.3 Inadequate fertilization

Very little fertilizers are used by the farmers in the 'Gher. Organic manure and inorganic fertilizers need to be added. The role of fertilizers were explained to the farmers. Although fertilizers dose will depend on the quality of the soil and water but with existing information the following doses in general were indicated:

Fertilizer

Quantity kg/ha

Cowdung

500

Urea

100

TSP

50

After fertilization the pond needs to be filled with water and the level should be maintained up to 60 cm. When water colour becomes green, the water level is increased gradually up to depth of 1 m. A seechi disk reading of 30-40 cm is required for stocking the post-larvae. The inlet of water should be strictly through the screen having 1.0 mm nylon net.

2.1.1.4 Insufficient water exchange

Farmers were appraised of the value of proper water exchange to maintain good water quality, to maintain required salinity, to remove excess metabolites, etc. In gher culture, at least water exchange should be 5% per day from the third week of stocking which needs to be increased up to 25% per day in the last month of the culture.

2.1.1.5 insufficient and irregular stocking

It has been observed that the farmers in Khulna region do not stock in adequate number. Nor they stock in time. As a result of these, neither they get optimum production nor they get proper healthy shrimp. The stocking density need to be at least 30,000-50,000/ha for gher culture. Even simple procedure of acclimatization or stocking procedures are not properly undertaken by farmers. Therefore, they were suggested the following:

2.1.1.6 Stocking

The stocking should be done in February/March. The stocking density can be maintained in the range of 30,000-50,000 PLs/ha depending on the availability of food, water depth and degree of water management.

2.1.1.7 Acclimatization

Three major factors need to be considered for acclimatization of fry: salinity, pH and temperature. Abrupt variation between salinity in the water of hatchery/nursery and pond is not desirable. Similarly, temperature variation should be avoided. pH of water should also be in the desirable range. If the variation of salinity and pH of water in pond and bag containing fry exceeds more than 3 ppt of salinity and 0.5 of pH; precaution is necessary for fry acclimatization. For a difference of every 0.5 pH or every 3 ppt salinity, an adjustment time of 15 minutes is recommended before stocking.

2.1.1.8 Stocking procedure

Stocking should be done early in the morning or at night when pond water is cool. The plastic bag containing fry should be floated in the pond for about half an hour to acclimatize the fry with the temperature of pond water. Then the mouth of the bag is opened and pond water is allowed to enter into the bag gradually. The fry is released slowly in the pond water.

2.1.1.9 Mortality Monitoring

After two days of stocking, depending on the mortality of seed, the ponds need to be restocked to compensate the mortality. If the mortality is above 50%, it is recommended that -preparation of pond should be undertaken afresh and fresh lot of seed is stocked. This is important because financial risk of culturing unhealthy fry would be greater than discarding the previously stocked fry.

2.1.1.10 Irregular monitoring of water quality

No monitoring of soil or water quality is done by the farmers. They were told of simple methods of identifying the deterioration in water/soil condition. However, scientific support is necessary for regular monitoring of physico-chemical parameters of the water/soil quality to improve the production.

2.1.1.11 No prevention or control of pests and predators

Undesirable fishes like Lates calcarifer, Eleutheronema tetradactylum, etc. enter into the cultured ponds during the intake of tidal water. These carnivorous fishes grow rapidly and become predator to the cultured shrimps. Some other shrimps and fishes compete for food with the cultured shrimp. Some crustaceans specially crabs make hole in the dyke. These predators and other undesired species should be completely eradicated from the pond by periodically operation of cast net.

2.2. Gher Management

The optimum water transparency should be 35-45 cm. Depending on the density of phytoplankton, water should be changed. If the seechi disk reading increases to more than 45 cm, the ponds needs to be fertilized at the rate of 30 kg/ha (Urea+TSP in the ratio of 3-5:1).

2.2.1 Water quality control

The desirable water quality for better growth of shrimp is given below which needs to be maintained as far as possible:

Parameters

Range

pH

7.5-8.5

Temperature

25-30°C

Salinity

15-25 ppt

DO

3-6 ppm

Turbidity

30-40 cm

Depth

1.2-1.6 m

NH3

0.1-0.5 mg/1

2.2.2 Feeding and management

The farmers were appraised of different aspects of feeding shrimp since the profitability of farm depends on the type of feed given to shrimp and feed management.

2.2.3 Disease and health monitoring

To maintain a disease free environment, selection of quality fry, good water ' condition and efficient feed supply are essential. If there is any type of disease, the farmer should start changing the water in the gher and consult FRI and DOF staff.

3. SEED PRODUCTION OF MULLET

Since mullet shows its potentiality of monoculture or polyculture with shrimp, it is important that FRI should stress on the culture of mullet.

For controlled production of mullet seed the hatchery is needed for which the following aspects are to be considered:

3.1 Site selection

The following criteria are to be considered for this purpose:

- Suitable land with transparent and pollution free sea water supply, having salinity of 28-32‰,
- Spawners availability
- Accessibility to electricity supply, proper road communication and other support and marketing facilities.

3.2 Hatchery facilities

- Broodstock maturation tank
- Algal and rotifer culture tank
- Brine shrimp incubator
- Holding tank for spawning, incubation and hatchling
- Larval rearing tank
- Water reservoir with filteration system
- Heating apparatus
- Blower and aerators
- Ancillary facilities (Laboratory and store room)
- Pump machine and standby generator

3.3 Hatchery Techniques

A layout of hatchery (Fig. 1) and a flowchart of hatchery operation (Fig. 2) are given which will be essential for proper hatchery management.

3.4 Broodstock collection

The brooders are available in the coastal belt and particularly during the breeding season in the month of December - January. Fishermen catch them with the help of beach seine.

3.5 Assessment of maturation and hormone injection

The ovarian maturity is measured by removing eggs from the female through a cannula of 0.7 mm diameter. When the eggs reach the tertiary yolk globule stage and have a mean egg diameter above 500 microns, the female should be injected with hormone. The dose of hormone is 120-400 h g/kg (LRH-Ag2) and given in two injections at an interval of 24 hours. Males are not injected.

3.6 Spawning and fertilization

Soon after the completion of hormone injection, the females and males are held in the spawning tank in the ratio of 1:3. Rapid abdominal distension showing proper gonadal hydration (Sinha - personal communication) and protrusion of the cloaca of female indicate the possibility of successful spawning.

After spawning the fishes are removed from the tank. The eggs remain in the spawning tank until the fertilization occurs. Aeration is done in the spawning tank. If there is any difficulty or delay in ovulation, the female is stripped and milt from the male is mixed for proper fertilization.

The ovulation time for injection varies from 8 to 52 hours at a temperature ranging from 20 to 27°C. Variation in time of ovulation also depends on the treatment of different hormones.

The first cleavage of eggs is observed after about one hour of spawning. The percentage of fertilization is then determined by microscopic observation of eggs.

3.7 Incubation

The fertile buoyant eggs rise to the surface when aeration in spawning tank is stopped. They are transferred into the incubator by syphoning directly or with a soft fine-mesh hand net. The eggs are washed gently under running irradiated and filtered sea water and dipped for a minute in the sea water containing potassium penicillin G (80 IU/ml) and streptomycin sulphate (0.05 mg/l).

A cylindrical incubator with cone-shaped bottom having diameter of 0.75-1.00 m and a depth of 1.5m is used to incubate the eggs at the rate of 75-100 per litre. Cleaning and sterilization of incubator before use is extremely important. Sea water is used and water exchange is not required. Water temperature is regulated within a range of 20-24°C with adequate aeration. Ten IU/ml penicillin and 0.01 mg/ml streptomycin are added daily into the incubator to prevent the chance of bacterial infection of the eggs. At the temperature range of 22-24°C, the incubation and hatching take place in 32-45 hours.

Fig. 1 Indoor arrangement of mullet hatchery.

Fig. 2: Flow Chart of Hatchery Operation (Nash & Shehadeh, 1980)

3.8 Larval rearing

The larval rearing tank is filled with bacterial free seawater. Good water quality having 28-30% of salinity is required for larval rearing. Water temperature should be maintained in the range of 20-24°C. Only 20% of water is exchanged each day for the first 25 days and the salinity to be reduced to 20-24%o. After 25 days a continuous exchange of water is done to completely replace the water in the tank every 24 hours. Salinity is brought as low as 15%o during 50 days of larval raising.

3.9 Larval feeding

The phytoplankton culture is given at 103 cells/ml which is also consumed by rotifers. The rotifer population is maintained at 5-10/ml. Copepods and amphipods are added at an initial density of 2-3/ml. The artificial feed (crumble of 100 micron) are mixed to make dough by adding freshwater and then broadcast so that the particles remain suspended for sometime. The left over feed is removed daily with suction device. After 45 days the young fish school together and are transferred after 50 days to the culture pond.

4. EXTENSION PAMPHLET


4.1 Polyculture of P. monodon and mullet in the Brackishwater ponds
4.2. Semi-intensive culture system of P. monodon


4.1 Polyculture of P. monodon and mullet in the Brackishwater ponds

Polyculture of shrimp and mullet has tremendous potential in the brackishwater of Bangladesh because of available land, water resources and favourable environmental conditions. The wild fry- of mullet may be collected from coastal creeks and mangrove swamps till hatchery is established and seed production technology is developed. Mullets polyculture with shrimp would provide maximum utilization of niches without using any supplementary feed for mullet.

The following aspects are considered for successful polyculture system.

Pond Preparation

Pond are usually irregular in size. It is desirable to make them uniform as much as possible. The size range should be in between 2-5 ha and depth of 1 m. The soil is to be leveled and the slope of the ground need to be maintained to keep water moving towards the gate during harvest.

Pond needs to be prepared properly to eliminate the pests and predators. The following steps are needed for pond preparation:

Drying, liming and filling

The pond should be dried after harvesting and then the bottom is ploughed. The liming dose is calculated depending upon the pH of the soil. The dose for lime application is given below:

Soil pH

Lime (Kg/ha)

4.0-4.5

1500

4.6-5.0

1250

5.1-5.5

1000

5.6-6.0

750

The pond will be filled with water to maintain the depth at least 20 cm.

Fertilization

The pond will be fertilized by both organic and inorganic fertilizer. The organic manure should be applied at the rate of 500 kg/ha, while inorganic at the rate of 150 kg/ha (Urea+TSP in the ratio of 2:1).

Although fertilizers dose will depend on the quality of the soil and water but with existing information the following doses in general are recommended:

Fertilizer

Quantity kg/ha

Cowdung

500

Urea

100

TSP

50

After fertilization, the pond needs to be filled with water and the level should be maintained up to 60 cm. When water colour becomes green, the water level is increased gradually up to depth of 1 m. A seechi disk reading of 30-40 cm is required for stocking the post-larvae. The inlet of water should be strictly through the screen having 1.0 mm nylon net.

Acclimatization

Three major factors need to be considered for acclimatization of fry: salinity, pH and temperature. Abrupt variation between salinity in the water of hatchery/nursery and pond is not desirable. Similarly temperature variation should be avoided. pH of water should also be in the desirable range. If the variation of salinity and pH of water in pond and bag containing fry exceeds more than 3 ppt of salinity and 0.5 of pH, precaution is necessary for fry acclimatization. For a difference of every 0.5 pH or every 3 ppt salinity, an adjustment time of 15 minutes is recommended before stocking.

Stocking

The stocking should be done in February/March. The stocking density can be maintained in the range of 30,000-50,000 PLs/ha of shrimp fry and 20,00-30,000 juveniles/ha of mullet depending on the availability of food, water depth and degree of water management.

Stocking procedure

Stocking should be done early in the morning or at night when pond water is cool. The plastic bag containing fry should be floated in the pond for about half an hour to acclimatize the fry with the temperature of pond water. Then the mouth of the bag is opened and pond water is allowed to enter into the bag gradually. The fry is released slowly in the pond water.

Mortality Monitoring

After two days of stocking, depending on the mortality of seed, the ponds need to be restocked to compensate the mortality. If the mortality is above 50%, it is recommended that preparation of pond should be undertaken afresh and fresh lot of seed is stocked. This is important because financial risk of culturing unhealthy fry would be greater than discarding the previously stocked fry.

Growout Management

The optimum water transparency should be 35-45 cm. Depending on the density of phytoplankton, water should be changed. If the seechi disk reading increases to more than 45 cm, the ponds needs to be fertilized at the rate of 30 kg/ha (Urea+TSP in the ratio of 3-5:1).

Water quality control

The desirable water quality for culture is given below which needs to be maintain as far as possible:

Parameters

Range

pH

7.5-8.5

Temperature

25-30°C

Salinity

15-25 ppt

DO

3-6 ppm

Turbidity

30-40 cm

Depth

1.2-1.6 m

NH3

0.1-0.5 mg/1

Feed specification and management

The profitability of farm depends on the quality of feed and feed management. Feed prepared by Saudi Bangla Fish Feed Ltd is recommended. The daily feed allotment and feeding schedule are presented in Table 1. Feed is recommended only for shrimp fry. They should be fed two times daily. The feed quality is measured with the total biomass of shrimp and is gradually decreased from 5% to 2%. Mullet will feed on phytoplankton.

Disease and health monitoring

To maintain a disease free environment, selection of quality fry, good water condition and efficient feed supply are essential. If there is any type of disease, the farmer should start changing the water in the cultured pond and inform the DOF and FRI staff.

Detection of problems and their solution

Problems/sign

Possible solution

1. Shrimp dying and sinking to the bottom due to low oxygen and high temperature

Dead shrimp be removed and immediate water and exchange is to be done

2. Active swimming at the water surface during day time due to low oxygen and high temperature

Immediate water exchange is to be done

3. Stunted growth due to lack of feed

Provision of proper feed and fertilization of water

4. Black gills/black spots on the body due to polluted pond water/soil

If possible completely drain out the pond and introduce fresh saline water

5. Phytoplankton bloom resulting in low oxygen level

Vigorous exchange of water should be done

6. Heavy accumulation of metabolites

Removal of decomposed matter and addition of fresh saline water

7. Lowering of salinity because of heavy rain causes mortality

Water exchange to be done immediately with fresh sea water

8. Early morning mortality due to hot, humid weather and progressively higher salinity

Replacing with fresh sea water

Economics

The production cost and net profit of 1 ha gher are given to have an approximate idea of the cost and benefit:

1. The production cost of 1 ha (one crop)

Line item

Quantity

Unit price

Total cost

(Tk.)

(Tk.)

a) Operation cost




Shrimp fry

30,000

1.50

45,000.00

Mullet

20,000

1.00

20,000.00

Pond preparation

-

-

10,000.00

Lime

1,000 kg

6.00

6,000.00

Chicken/cattle




manure

1,000 kg

2.00

2,000.00

Urea

100 kg

10.00

1,000.00

TSP

50 kg

10.00

500.00

Feed

1,000.97

kg 42.00

44,938.74

Power

-

-

10,000.00

Labour

2 m/m

80.00

44,800.00

Miscellaneous

-

-

2,000.00

Sub-total


Taka

152,238.74

b) Fixed cost




Lease land money

-

-

10,000.00

Depreciation of pump and other Machineries

-

-

8,000.00

Overhead cost

-

-

2,000.00

Sub-total


Taka

20,000.00

Grand total

-

Taka

172,238.74

II. Income by selling products:



Shrimp

718.62 X 300.00/kg

215,586.00

Mullet

860.03 X 50.00/kg

43,001.50

Total


Taka

258,587.50

III. Net profit




Tk. 258,587.50-172,238.74 = Tk. 86,348.76



Table 1: Feeding chart for shrimp fry (Samudra, 1991).

4.2. Semi-intensive culture system of P. monodon

Semi-intensive culture of Penaeus monodon has potential in Bangladesh because of available land, water resources, and environmental condition. This system of culture would require less technical expertise, less capital investment, less operational costs, and thus, lower the cost of production of shrimp.

Site Selection

Suitable site is one of the most important factors which determines the success or failure of any farming system. The government agency has already identified the suitable areas for semi-intensive culture and farmers are advised to contact the DOF staff for suitable land. However, the supply of pure freshwater and sea water with 15-25 ppt salinity are essential to be in the vicinity of the farm. Electricity supply is essential along with proper road.

Farm Management

Pond preparation

Pond preparation includes drying, flushing, liming, filling and levelling, all these processes require at least from 15 to 45 days depending on the weather.

After the crop is harvested, the pond should be dried. The pond bottom is exposed to sun till they dry and then the bottom is ploughed. The pond should be flushed with saline water and drained subsequently. Moist soil sample should be collected to know the pH. Lime should be applied properly throughout the pond bottom so as to adjust the soil pH to around 7.0. The quantity of lime to be applied as per the pH value.

Soil pH

Lime (Kg/ha)

4.0-4.5

1500

4.6-5.0

1250

5.1-5.5

1000

5.6-6.0

750

Fertilization

The pond should be fertilized by both organic and inorganic fertilizer. The organic manure will be applied at the rate of 500 kg/ha, while inorganic at the rate of 150 kg/ha (Urea+TSP in the ratio of 2:1).

Although fertilizers dose will depend on the quality of the soil and water but with existing information the following doses in general were indicated:

Fertilizer

Quantity kg/ha

Cowdung

500

Urea

100

TSP

50

After fertilization, the pond needs to be filled with water and the level should be maintained up to 60 cm. When water colour becomes green, the water level is increased gradually up to depth of 1 m. A seechi disk reading of 30-40 cm is required for stocking the post-larvae. The inlet of water should be strictly through the screen having 1.0 mm nylon net.

Acclimatization

Three major factors need to be considered for acclimatization of fry: salinity, pH and temperature. Abrupt variation between salinity in the water of hatchery/nursery and pond is not desirable. Similarly temperature variation should be avoided. pH of water should also be in the desirable range. If the variation of salinity and pH of water in pond and bag containing fry exceeds more than 3 ppt of salinity and 0.5 of pH, precaution is necessary for fry acclimatization. For a difference of every 0.5 pH or every 3 ppt salinity, an adjustment time of 15 minutes is recommended before stocking.

Stocking

Stocking density depends on the culture system including the availability of food, depth of water and efficiency of water management. In this semi-intensive culture system, two different stocking densities such as 5 PLs/m2 and 10 PLs/m2 have been recommended and the time of stocking is February - March and September - October.

Stocking procedure

Stocking should be done early in the morning or at night when pond water is cool. The plastic bag containing fry should be floated in the pond for about half an hour to acclimatize the fry with the temperature of pond water. Then the mouth of the bag is opened and pond water is allowed to enter into the bag gradually. The fry is released slowly in the pond water.

Mortality Monitoring

After two days of stocking, depending on the mortality of seed, the ponds need to be restocked to compensate the mortality. If the mortality is above 50%, it is recommended that preparation of pond should be undertaken afresh and fresh lot of seed is stocked. This is important because financial risk of culturing unhealthy fry would be greater than discarding the previously stocked fry.

Growout Management

Phytoplankton management

The phytoplankton density is deduced form transparency data obtained by a secchi disk. The optimum water transparency should be 35-45 cm. Sometime because of the presence of excessive silt the water looks cloudy. It is then important that water should be exchanged and left undisturbed to settle the silt.

In case of dense algal bloom secchi disk reading is about 25 cm or less. Then again water should be changed as soon as possible. Water exchange should be continued until the secchi disk reading is 35-45 cm. In case the reading increases to more than 45 cm, fertilization is necessary with 30 kg/ha of urea and TSP at a ratio of 3-5:1, respectively.

Water quality control

The desirable water quality for better growth of shrimp is given below which needs to be maintain as far as possible:

Parameters

Range

pH

7.5-8.5

Temperature

25-30°C

Salinity

15-25 ppt

DO

3-6 ppm

Turbidity

30-40 cm

Depth

1.2-1.6 m

NH3

0.1-0.5 mg/1

Feed specification

Production and profit depend on the availability of nutrients from both natural food and artificial feed. The artificial feed prepared by Saudi Bangla Fish Feed Ltd. is recommended.

Feed Management

The daily feed allotment and feeding schedule should be as shown in Tables 2 and 3.

Detection of problems and their solution

Problems/sign

Possible solution

1. Shrimp dying and sinking to the bottom due to low oxygen high temperature

Dead shrimp be removed and immediate water exchange is to be done

2. Active swimming at the water surface during day time due to low oxygen and high temperature

Immediate water exchange is to be done

3. Stunted growth due to lack of feed

Provision of proper feed and fertilization of water

4. Black gills/black spots on the body due to polluted pond water/soil

If possible completely drain out the pond and introduce fresh saline water

5. Phytoplankton bloom resulting in low oxygen level

Vigorous exchange of water should be done

6. Heavy accumulation of metabolites

Removal of decomposed matter and addition of fresh saline water

7. Lowering of salinity because of heavy rain causes mortality

Water exchange to be done immediately with fresh sea water

8. Early morning mortality due to hot, humid weather and progressively higher salinity

Replacing with fresh sea water

Economics

To assess the economic returns two examples are shown based on study by Samudra (1991)

Penaeus monodon with stocking density of 5 PLs/m2

1. Production cost (one cycle)

Bond area

10,000 m2

Production level

1363.13

Production period

120 days

Survival rate

75%

Total feed

1922.92 kg

Production size

36.35 gm

SI. No.

Line item

Quantity

Unit cost

Total cost

Cost/kg

% of Total cost

Tk.

Tk.

Tk.

1.

PL15

50,000

1.5/pc

75,000.00

55.02

34,680

2.

Pond preparation



10,000.00

7.34

4,624

3.

Lime (kg)

1,000

6/kg

6,000.00

4.40

2,774

4.

Teasced (kg)

120

50/kg

6,000.00

4.40

2,774

5.

Fertilizer (kg)







Organic

1,000

2/kg

2,000.00




Urea

100

10/kg

1,000.00




TSP

50

10/kg

500.00




Total



3500.00

2.57

1,618

6.

Zeolitc (kg)

500

10/kg

5,000.00

3.67

2,312

7.

Fuel



15,000.00

11.00

6,936

8.

Feed (kg)

1922.92

42/kg

80,762.64

59.25

37,345

9.

Labour

5 mm/

80/person

12,000.00

8.80

5,550

10.

Miscellaneous



3,000.00

2.20

1,387


Total



216,262.64

158.13

100.00

11.

Fixed cost including depreciation, overhear and miscellaneous expenses (50%)



8,000.00




Total



224,262.64



Income from selling shrimp 300 x 1363.13 = Tk. 408,939.00
Net profit = 408,939.00-224,262.64 = Tk. 184,576.36

Penaeus monodon with stocking density of 10 PLs/m2.

1. Production cost (one cycle)

Pond area

10,000 m2

Production level

2275 kg

Production period

120 days

Survival rate

65%

Total feed

3213 kg

Production size

35 gm

Sl. No.

Line item

Quantity

Unit cost

Total cost

Cost/kg

% of Total cost

Tk.

Tk.

Tk.

1.

PL15

100,000

1.5/pc

150,000.00

65.93

41,964

2.

Pond preparation



10,000.00

4.40

2,798

3.

Lime (kg)

- 1,000

6/kg

6,000.00

2.64

1,679

4.

Teasced (kg)

120

50/kg

6,000.00

2.64

1,679

5.

Fertilizer (kg)







Organic

1,000

2/kg

2,000.00




Urea

100

10/kg

1,000.00




TSP

50

10/kg

500.00




Total



3,500.00

1.54

0,979

6.

Zeolitc (kg)

500

10/kg

5,000.00

2.20

1,398

7.

Fuel



25,000.00

10.99

6,994

8.

Feed (kg)

3213

42/kg

134,946.00

59.32

37,753

9.

Labour

5 m/m

80/person

12,000.00

5.27

3,357

10.

Miscellaneous



5,000.00

2.20

1,399


Total



357,446.00

148.13

100.00

11.

Fixed cost including depreciation, overhead and miscellaneous expenses (50%)



10,000.00




Total



367,446.00



Income from selling shrimp 300 x 2275.00 = Tk. 682,500.00
Net profit = 682,500.00-367,446.00 = Tk. 315,054.00

Table 2. Feeding Chart for Shrimp Fry (SD = 5 ind/m2) (Samndra, 1991)

Table 3. Feeding Chart for Shrimp Fry (SD = 10 PLs/m2) (Samndra, 1991)

5. KEYS FOR IDENTIFICATION OF POST-LARVAL SHRIMP AND PLANKTON

To have a base line data on biodiversity of estuarine organisms, a proper investigation was necessary when plenty of brackishwater resources such as phytoplankton and zooplankton of different taxa are indiscriminately caught and being killed in the process of wild seed collection. However, FRI made very extensively effort for collection of such samples while seeds of shrimp are collected. Some analyses were made. However, it needs systematic identification and therefore, the scientists were trained ^in identifying those. To assists them a key was prepared which will help them in identification of shrimps, and plankton. The key is attached as an annexure I.

6. RECOMMENDATIONS

- As 'gher' fisheries is very popular to the coastal farmers of the Khulna region, technical supports by the FRI scientists may be provided to upgrade their experiences.

- The present production in gher need to be related with the physico-chemical conditions of water and soil so that present management method may be upgraded suitably.

- Considering the infrastructural and management facilities, the gher size should not exceed beyond 2 hectares and culture period may be around 120 days.

- Shrimp is cultured for four months only because of required salinity of water is available only during this period. Therefore, another crop is necessary to properly utilize the "gher'. In this respect mullet culture may be encouraged as a second crop. Also mixed culture of mullet & shrimp is recommended to reduce the adverse affect of over production of phytoplankton.

- It was observed that several penaeid species such as Penaeus merguiensis, P. indicus, P. japonicus, P. semisulcatus, Metapenaeus monoceros and P. brevicornis are available along with P. monodon in the coastal area of the country. As these species have marketable values, their farming technology may be evolved.

- P. monodon and mullet hatchery may be established where salinity is about 28% and also freshwater source is available.

- FRI scientists should be trained in China, Philippines, North Korea on mullet breeding and seed production.

- A base line data bank on estuarine biodiversity is urgently to be set up at FRI where scientists are already doing some useful work in this regards. Farmer training and their participation are essential for collection, preservation and conservation of biodiversity.

7. REFERENCES

Ahmed, S. 1984. Zooplankton Communities of the estuarine area of Satkhira, Bangladesh with special reference to Ichthyoplankton.

Apud, F.D., Primavera, J.H. and Torres Jr. P.L. 1983. Farming of prawns and shrimps. Extension Manual No. 5 SEAFDEC Aquaculture Department, Iloilo, Philippines, 67 pp.

BOBP. 1993. A seminar-workshop on Setbag net fishery of Bangladesh held at Cox's Bazar organized by BOBP/FAO.

Das, N.G. 1992. Artificial breeding of mullet (Liza subviridis);

Final Report of Contract Research Project co-ordinated by the Bangladesh Agricultural Research Council (BARC), Farmgate, Dhaka, 55 pp.

Das, N.G., Alam, M.M. and Deb, A.K. 1992. Study on colossal loss of shell fish and fin fish postlarvae for indiscriminate catch of Penaeus monodon fry along with the Cox's Bazar-Teknaf coast.

Davls, C.C. 1955. The Marine and Freshwater Plankton. Michigan State University Press, USA, 562 pp.

Fisheries Research Institute (FRI). 1991. FRI Annual Progress Report. FRI, Mymensingh, Bangladesh.

Haque, S.M.A. 1983. Study on Phytoplankton of the Mathamuhuri Estuary and Fish Ponds in the Vicinity. M.Sc. Thesis, IMS, C.U., 174 pp.

Khan, Y.S.A. 1991. Studies on some aspects of Ichthyoplankters in the Chakaria Mangroves, Chittagong. Ph.D. Thesis, Fisheries Research Lab., Zool. Dept., R.U., Bangladesh, 222 pp.

Lee, C.S., Tamara, C.S., Miyamoto, G.T. and Kelley, C.D. 1987. Induced spawning of grey mullet (Mugil cephalus) by LRH-A2. Aquaculture, 62:327-336.

Mahmood, N. and Zafar, M. 1990. Postlarvae of the common and commercially important penaeid shrimps of Bangladesh coastal waters. Bangladesh J. Agr., 15(2):83-103.

Mohi, S.A. 1977. Distribution of Ichthyoplankton in the Karnafully River Estuary in relation to salinity. M.Sc. Thesis, IMS, C.U., 87 pp.

Motoh, H. 1981. Studies on the fisheries biology of the giant tiger prawn, Penaeus monodon in the Philippines. SEAFDEC Aquaculture Department, IIoilo City, Philippines, 128 pp.

MPO (Master Plan Organization) 1986. Technical report no. 18: Coastal Shrimp aquaculture resources. Ministry of Irrigation, Water Development and Flood Control. 105 pp.

Munro, I.S.R. 1982. The Marine and Freshwater Fishes of Ceylon. Soni Reprints Agency, Gandhi Nagar, Delhi- 110031, 351 pp + 56 pls.

Nash, C.E. and Shehadeh, Z.H. 1980. Review of breeding and propagation techniques for grey mullet, Mugil cephalus L. ICLARM Studies and Review, 3: 11-77.

Newell, G.E. and Newell, R.C. 1963. Marine Plankton: A Practical Guide. Hutchinson Educational Ltd. 3 Fitzroy Square, London W 1, 244 pp.

Oren. O.H. 1981. Aquaculture of Grey Mullets. International Biological Programme, 26 Cambridge University Press, London New York, 507 pp.

Salam, M.A. 1977. Algal Flora of the Karnafully Estuary and ecological observations of changes in the growth of some intertidal algae of Potenga Coast. M.Sc. Thesis, IMS, C.U., 108 pp + 19 pls.

Samudra, H.D., 1991. Management of a Shrimp Farm in Indonesia. American Soybean Association, Vol. AQ35, 541 Orchard Road, #11-03 Liat Towers, Singapore 0923.

Wickstead, J.H. 1965. An Introduction to the Study of Tropical Plankton. Hutchinson and Co. (Publishers) Ltd., 178-202 Portland Street, London W1, 156 pp.

Zafar, M. 1992. Study on some hydrological aspects of the southeastern parts of Bangladesh coastal waters in the Bay of Bengal. M.S. Dissertation, Royal Belgium Institute of National Science, Free University of Brussel, V.U.B., Belgium, 178 pp.

8. ANNEXURE


8.1 Keys for identification of post-larval shrimps and plankton


8.1 Keys for identification of post-larval shrimps and plankton

KEY TO THE POSTLARVAL PENAEIDS BASED ON MORPHOLOGICAL AND CHROMATOPHORE PATTERNS (The number shown on the right side indicates the additional characters of the species described under the serial number as shown on the left side).

1. Postlarvae relatively short, generally coloured a mottled grey or brown compared to Penaeus; rostrum usually without ventral teeth; telson with 8+1+8 or 7+7 spines on sides and distal margin.................... 2.

Postlarvae relatively long, reddish brown to yellowish brown or colourless; rostrum usually with ventral teeth; telson with 8+8 spines on-sides and distal margin........................................ 6.

2. Telson with 8+1+8 spines, median posterior spine stout and much longer than adjacent spines; median dorsal spines on abdominal segment absent; rostrum lanceolate with 2 dorsal spines....................................Parapenaeiopsis stylifera.

Telson with 7+7 spines on sides and distal margin................. 3

3. Chromatophores present on outer and inner rami of uropods...........4

Chromatophore present on inner rami only, outer rami colourless...................... Metapenaeus monoceros

4. A row of Chromatophores present on inner and outer rami of uropods; rostrum with 3 spines......................... Metapenaeus brevicomis

Chromatophores not continuous, may be 1 in number, rostrum with 2 or 4 spines.............................................................. 5

5. A single chromatophore at tip of each uropod ramus; rostrum with 4 spines; long setae on disto-lateral aspect of 6th abdominal segment............................................... Metapenaeus affinis

A prominent chromatophore in the middle of each uropod ramus; rostrum with 2 spines; no setae on disto-lateral aspect of 6th abdominal segment.......................................Metapenaeus dobsoni

6. Telson with Chromatophores in disal half only, median dorsal spine present on 5th and 6th abdominal segments............. Penaeus indicus

Telson with Chromatophores from base to distal end.................7

7. Outer rami of uropods without chromatophores.......................8

Outer and inner rami of uropods with chromatophores................ 9

8. Number of chromatophores on 6th abdominal segment more than twelve, antero lateral chromatophores of 6th abdominal segment absent; chromatophores on 6th segment each separate or confluent; inner ramus of uropods with a single chromatophore near base usually hidden by telson...................... Penaeus japonicus

Number of chromatophores on 6th abdominal segment less than seven; anterolateral chromatophores of 6th abdominal segment present; inner rami of uropods with 3-4 chromatophores in the middle region..................................... Penaeus merguiensis

9. Number of chromatophores on 6th abdominal segment less than twelve, anterolateral chromatophore of 6th abdominal segment present; distal half of inner and outer rami of uropods with numerous chromatophores.............. Penaeus semisulcatus

Number of chromatophores on 6th abdominal segment more - than twelve, dense and thickly continuous; antero-lateral chromatophore of 6th abdominal segment absent; inner and outer rami of uropods with a row of chromatophores along the median margin.................................................. Penaeus monodon

KEY TO POSTLARVAL PENAEUS BASED ON MORPHOLOGICAL CHARACTERS

1. Rostrum stout and not reaching tip of eye; spinules on 6th abdominal segment present; antennal spine prominently present; caraface slightly longer than 6th abdominal segment.............................................................. Penaeus japonicus

Rostrum slender and extending beyond tip of eye; spinules on 6th abdominal segment absent; antennal spine absent or minute; caraface slightly or distinctly shorter than 6th abdominal segment......................................................................................... 2

2. Inner (lower) antennular flagellum nearly 1.6 times as long as outer (upper) flagellum, exceeding the latter by one distal segment.................................................. 3

Inner antennular flagellum more than 1.6 times as long as outer flagellum, exceeding the latter by more than one distal segment.................................................................. 4

3. Rostrum exceeding eye, 1-3 dorsal teeth.................:.......................... Penaeus indicus

Rostrum exceeding eye, 3-4 dorsal teeth.................................... Penaeus merguiensis

4. Inner antennular flagellum 1.6 to 2.0 times as long as upper flagellum, exceeding the latter by two distal segments.................................................... Penaeus semisulcatus

Inner antennular flagellum more than 2.0 times as log as upper flagellum, exceeding the latter by three distal segments.................................................... Penaeus monodon

The following authors were consulted: Apud et al (1983); Motoh (1981) and Mahmood and Zafar(1990).

IDENTIFYING KEY TO ICHTHYOPLANKTON OF BANGLADESH

Ichthyoplankton are the representatives of their adult fishes. Their diagnostic characters develop when they appear in their post-larval forms:

Key to the Orders:

1. Body asymmetrical with eyes both sameside of head............ Order: Pleuronectiformes

Body bilaterally symmetrical with eyes on opposite side of head.................................2

Number of chromatophores on 6th abdominal segment more than twelve, dense and thickly continuous; antero-lateral chromatophore of 6th abdominal segment absent; inner and outer rami of uropods with a row of chromatophores along the median margin............................................... Penaeus monodon

KEY TO POSTLARVAL PENAEUS BASED ON MORPHOLOGICAL CHARACTERS

1. Rostrum stout and not reaching tip of eye; spinules on 6th abdominal segment present; antennal spine prominently present; caraface slightly longer than 6th abdominal segment......................................................................... Penaeus japonicus

Rostrum slender and extending beyond tip of eye; spinules on 6th abdominal segment absent;-antennal spine absent or minute; caraface slightly or distinctly shorter than 6th abdominal segment......................................................................................... 2

2. Inner (lower) antennular flagellum nearly 1.6 times as long as outer (upper) flagellum, exceeding the latter by one distal segment.................................................. 3

Inner antennular flagellum more than 1.6 times as long as outer flagellum, exceeding the latter by more than one distal segment.................................................................. 4

3. Rostrum exceeding eye, 1-3 dorsal teeth............................................ Penaeus indicus

Rostrum exceeding eye, 3-4 dorsal teeth.................................... Penaeus merguiensis

4. Inner antennular flagellum 1.6 to 2.0 times as long as upper flagellum, exceeding the latter by two distal segments.................................................... Penaeus semisulcatus

Inner antennular flagellum more than 2.0 times as log as upper flagellum, exceeding the latter by three distal segments.................................................... Penaeus monodon

The following authors were consulted: Apud et al (1983); Motoh (1981) and Mahmood and Zafar(1990).

IDENTIFYING KEY TO ICHTHYOPLANKTON OF BANGLADESH

Ichthyoplankton are the representatives of their adult fishes. Their diagnostic characters develop when they appear in their post-larval forms:

Key to the Orders:

1. Body asymmetrical with eyes both sameside of head............ Order: Pleuronectiformes

Body bilaterally symmetrical with eyes on opposite side of head.................................2

2. Ventral fin absent.......................................................................................... 3

Ventral fin present......................................... 8

3. Body extremely long, eel-like or ribbon-like.................................................................. 4

Body short, not eel-like or ribbon-like................................................ 6

4. Body cylindrical; caudal fin present............................................................................. 5

Body flattened and ribbon-like; caudal fin absent.......... Order: Persiformes (Sub-Order: Trichiuroidei)

5. Dorsal and anal fins without spines.......................................... Order: Anguilliformes

Dorsal and anal fins with spines.......................................... Order: Mastacembeliformes

6. Scales modified into minute sharp granules, needle-like spines, calcarious plates or fused into bony structure.......................................................... Order: Tetradontiformes

Scales when present, normal overlapping type............................................................ 7

7. Large sub-cylindrical fishes with upper jaw prolonged into a sword................................

................................................................ Order: Perciformes (Sub-Order: Scombroidei)

Small oval fishes with upper jaw not prolonged into a sword..........................................

.............................................................. Order: Perciformes (Sub-Order: Stromateoidei)

8. Ventral fin abdominal.................................................................................................... 9

Ventral fin thoracic or jugular..................................................................................... 15

9. Body naked or with bony plates or rings (several pairs of barbels)................................. Order: Cypriniformes (Sub-Order: Siluroidei)

Body with normal overlapping scales..................................................................................... 10

10. One dorsal fin..................................................................................... 11

Two dorsal fins..................................................................................... 13

11. Lateral when present, situated on upper half of sides, never forming a raised ridge....................12

Lateral line extremely low on sides, forming a raised ridge; tail forked, truncate, ventrals with 6 rays............................ Order: Beloniformes

12. Head scaly and depressed; ventrals moderately large......... Order: Cyprinodontiformes

Head naked and compressed; ventrals small................................. Order: Clupeiformes

13. First dorsal with soft rays only second dorsal adipose................. Order: Scopeliformes

First dorsal with spines only; second dorsal with soft rays......................................... 14

14. Pectoral with lowermost rays detached and filamentous...................... Order: Polynemiformes

Pectoral fin entire with no free rays................................................. Order: Mugiliformes

15. Ventral fin closed together or united, forming a sucking disk............... Order: Perciformes (Sub-Order: Gobioidei)

Ventral fins far apart, never forming a sucking disc.......................... Order: Perciformes (Sub-Order: Percoidei)

Key to the Families of Order Clupeiformes

1. Lateral line present..................................................................................... 2

Lateral line absent..................................................................................... 3

2. Branchiostegals 4............................................................................... Family: Chanidae

Branchiostegals more than 20 (Body slender, scales small, fin without filaments).............................. Family: Elopidae

3. Mouth moderate, terminal: maxillary in 3 pieces

(Body compressed, with bony serrae................................................... Family: Clupeidae

Mouth very long, usually inferior; maxillary very long....................... Order: Engraulidae

Key to the Families of Sub-Order Percoidei

1. Two separate dorsal fins................................................................ Family: Sillagonidae

One continuous dorsal fin, spinous..................................................................................... 2

2. Anal with 1 or 2 spines..................................................................... Family: Sciaenidae

Anal with 3 to 12 spines..................................................................................... 3

3. A scaly process in axil of ventrals, or ventrals minute or vestigial................................ 4

No scaly process in axil of ventrals............................................... Order: Theraponidae

4. Teeth on palate well-developed..................................................................... 5

No teeth on palate, or a few on vomer only................................................................ 6

5. Dorsal fin deeply notched..................................................................... Family: Latidae

Dorsal fin not notched....................................................................... Family: Lutianidae

6. Mouth protractile (Top of head with bony ridges)........................ Family: Leiognathidae

Mouth not protractile..................................................................................................... 7

7. Teeth small, in brush-like or villiform bands in jaws

(Anal with 4 spines).................................................................... Family: Scatophagidae

Teeth larger, conical or molariform in several series
(Eyes small, dorsal and anal spines weak).................................. Family: Nemipteridae

Key to the Families of Sub-Order Gobioidei

Pelvics entirely separate.................................................................... Family: Eleotridae
Pelvics fully united............................................................................... Family: Gobiidae
Pelvics united at base only....................................................... Family: Periophthalmidae

Order: Ciupeiformes

Family: Elopidae
Species: Elops machnata

B. 20-25; A. 13-17; L. lat. 100-120; Branchiostegals 27-34; scales small and thin; fin with scaly basal sheath; ventral rays 17-18.

Family: Chanidae
Species: Chanos chanos

D. 14-16; A. 10-11; L. lat. 75-80; body compressed, torpedo shaped; head naked; caudal deeply forked; 10-11 pelvic rays.

Family: Clupeidae

Oblong fishes; belly keeled with scutes along ventral edge; branchiostegals 6-15: no lateral line.

Species: Tenualosa ilisha

D. 18-20; A. 18-21; lateral scales 45-48; Tr. 17-20; ventral scutes (17-19) + (11-13).

Species: Ilisha filigera

D. 18-20: A. 44-51: lateral scales 50; Tr. 15-16; ventral scutes(22-23) + (10-12).

Species: Ilisha elongate

D. 13; A. 38; lateral scales 17; ventral scutes (19-23) + (8 -11).

Family: Engraulidae

Body elongated and compressed; snout bluntly rounded; no lateral line; eyes completely covered with skin; belly win numerous keeled abdominal scutes.

Species: Setipinna taty

D. 16; A. 19-21; lateral scales 37-42; Tr. 8-9; predorsal scales 20-22; ventral scales 4-5 before pelvics.

Species: Coilia ramcarati

D. 14-15; A. 35-42; lateral scales 35; abdominal scutes 5+8; caudal continuous with long anal.

Order: Perciformes
Sub-order: Trichiuroidei
Family: Trichiuridae

Elongate, highly compressed body, without scales; dorsal and anal fins feeble but long and with numerous rays; body tappers behind to a point; no caudal fin.

First anal spine well-developed, more than half diameter of eye........................ Trichiurus savala

First anal spine minute, not longer than following one............ Trichiurus haumela

Family: Sclaenidae

Body elongate, robust; 2 weak anal spines; caudal truncate to weakly emerginate.

Species: Johnius dussumieri

D. X; 1.28-32; A. II, 8; L. lat. 50: Tr. 5 + (10-12); chin with 5 pores; caudal rounded.

Species: Johnius argentatus

D. X-XI; I, 24-28; L. lat. 60 along above 85-90, along below 70; Tr. (9-10) + 18; shoulder scale strongly serrated; 3 pores on top of snout, 5 pores on chin; lower gill rakers 14-15.

Species: Otolithus maculatus

D. IX-X; I,1,30; A. H, 10-12; L. lat. 85, along above 95; Tr. (13-14) + (25-26); head pointed; 3 pores on snout; operculum with 2 weak spines; body and fins with dark blotches.

Family: Leiognathidae

Body compressed with minute scales; mouth extremely protractile; dorsal and anal with basal sheath.

Species: Leiognathus ruconius

D. VIII; 16, A. III, 14; mouth very oblique; body ovate, depth 11/2 -13/4.

Species: Leiognathus equulus

D. VIII; 15-16, A. III, 14; depth 2-21/2; L. lat. 60, terminating at caudal base; second dorsal spine more than twice in body length.

Family: Sillagonidae

Robust elongate tapering body; small scales; two dorsals, first with 10-11 spines; anal with 2 spines.

Species: Sillago domina

D. X-XI; 1:1,20-23, A. II, 21-24; L. lat. 70-73; Tr. (5-6) + (10-12).

Family: Theraponidae

Species: Therapon jarbua

D. XI-XII; 10-11; A. III. 7-9; L. lat. 82-84; Tr. (15-16) + (23-25); predorsals 20-25, cheek scales 6-7; 3 dark longitudinal cross-bands, curved downwards.

Family: Latidae

Species: Lates calcarifer

D. VII-VIII; I, 10-11; A. 111. 7-8; L. lat. 52-61; Tr. 6+13; predorsals 27-28, compressed, elongate body; large protractile mouth with exposed maxillary; lower edge of preopercle with spines; tongue smooth; lower gill-rakers 16-17.

Family: Scatophagidae

Species: Scatophagus argus

D. XI; 16-18; A. IV, 14-15; depth 13/4 - 2; L. lat. 95-120; Tr. 80 between dorsal and ventral fins; rostrodorsal provide strongly ascending and followed by a deep concavity above the eyes; body agular.

Family: Lutlanidae

Species: Lutianus lutianus

D. X; 14-15; A. III, 8-9; L. lat. 48-52; Tr. 8+17; depth 21/2; feeble notch in preopercle; two large blotches on back.

Family: Nemipteridae

Species: Odontoglyphis rubicundus

D. X; 9; A. III, 7; L. lat. 48-49; Tr. 4+11; pelvics and upper caudal lobe with filamentous rays; caudal forked.

Family: Goblidae

Species: Oligolepis acutipennis

D. VI; I, 10-11; A. I, 10-11; P. 10-21; L. lat. 27-30; Tr. 7-8; body elongate. compressed, depth 5-6; teeth anteriorly in several rows; caudal lanceolate, longer than head

Species: Glossogobius giuris

D. VI; I, 8-9; A. I. 7-8; P. 17-21; L. lat. 28-36; Tr. 8-14; predorsals 12-30; body elongate, anteriorly cylindrical, posteriorly compressed; head pointed, depressed; caudal obtuse, as long as head.

Species: Apocryptes lanceolatus

D. V; I, 30; A. I, 29; P. 17-20; very elongate body, cylindrical anteriorly and compresses posteriorly; head sub-cylindrical; 24 pointed teeth in both Jaws; caudal pointed.

Species: Sicyopterus gynnauchen

D. VI; I, 9-10; A. I, 10; P. 10; L. lat. 52-55; Tr. 14-15; predorsals 11-12; body cylindrical anteriorly, compressed posteriorly; depth 7-8; caudal emerginate.

Family: Periophthalmidae

Species: Periophthalmus koelreuteri

D. 10-17; I,11; A. I.10-11; P. 13; L. lat. 70-90; Tr. 2 + (12-13); predorsal 35; depth 6.7; dorsal separate; caudal obliquely truncate.

Family: Eleotridae

Species: Eleotris fusca

D. VI; 1,8; A. I, 8; P. 15-18; L. lat. 60-65; Tr. 16-19; predorsals 50; depth 5-6; caudal cycloid before first dorsal, ctenoid posteriorly; head depressed; dorsals separate, caudal oblong.

Species: Eleotris porocephala

D. VI; 1. 8-9; A. I. 6-7; P. 15; L. lat. 38-40; Tr. 11-13: predorsals 24-26; body anteriorly cylindrical, posteriorly compressed; depth 5-6; head depressed; snout pointed, head totally scaled; caudal rounded.

Family: Stromateidae

Ovate, compressed body covered with small scales; head scally; mouth small with weak jaws; dorsal with a distinct spinous portion but spines embedded in skin.

1. Posterior portion of lateral line keeled...................................... Parastromatus niger

Lateral line not keeled........................................................ 2

2. Posterior part of the dorsal comprising rays of equal length; caudal deeply forked...... Pumpus argenteus

Posterior part of dorsal comprising rays of gradually decreasing height; caudal emerginate..................................................... Pumpus chinensis

Family: Scombridae

Species: Rastrelliger kanagurta

D. X; 12; 5. A. 12; 5. P. 2. 17; depth 4-4.7; head longer than heigh; a single series of small teeth In jaws; no teeth on palate; a row of 16 spots along back near base of dorsal; dorsal yellow with black tips.

Order: Cypriniformes

Family: Bagridae

Species: Mystus gulio

D. II, 6-7; A. III-IV, 10-12; P. I., 7-9; nasal barbels reach hind edge of preopercle; body subcylindrical; head sub-conical; 4 pairs of barbles; dorsal and pectoral with spines; adipose fin present; caudal fin forked.

Family: Cobitiidae

Species: Cobitis botia

D. III-IV, 10-11; A. III, 5; P. 1.10-12; Tr. (16-18) + (11-15); predorsal 52; barbles 6-8; mouth inferior: dorsal with 5 rows of black spots; caudal with 7 V-shaped black bars.

Order: Beloniformes

Family: Hemirhampidae

Species: Hamirhampus gaimardi

D. 14-15; A. 14-16; L. lat. 50; lower jaw developed into a long bony beak; upper jaw broader than long; caudal deeply forked.

Order: Cyprinodontiformes

Family: Cyprinodontidae

Species: Panchax melastigma

D. 6-7; A. 20-24; L. lat. 27; L. Tr. 9-11; ventrals without prolonged rays; anals with 20-24 radials; caudal rounded.

Order: Anguilliformes

Species: Ophichthys bore

Gill-openings moderate slits; tongue present; no scales; dorsal and anal poorly developed; tail pointed; pectoral fin present; teeth conical.

Order: Mugiliformes

Family: Mugilidae

Fishes without lateral line; elongate body; head broad and flattened; 4 spines in dorsal fin.

Key to Genera

1. Hind tip of maxilla not curved down below tip of premaxilla; adipose eyelid present................ Mugil

Hind tip of maxilla curved down below tip of premaxilla; adipose eyelid absent........... 2

2. Scales ctenoid or cycloid but with no digitations on hind margin; tip of maxilla apparent when mouth closed..................... Liza

Scales cycloid, hind margin with digitations; maxilla tip hidden beneath tendon.................... Valamugil

Species: Mugil cephalus

Posterior tip of upper jaw not curved down and hidden when mouth closed; several rows of teeth in upper Ho; origin of first dorsal fin nearer to snout tip than to caudal fin base; origin of second dorsal fin behind vertical from origin of anal fin; pectoral fin with an auxiliary scale; anal fin with 8 son rays; caudal fin forked; scales in lateral series 38-42.

Species: Liza subviridis

Posterior tip of upper Jaw strongly curved down and still visible when mouth closed; origin of first dorsal fin nearer to snout tip than to caudal fin base; pectoral fin very short, with no auxiliary scale; caudal fin slightly forked; scales In lateral series 30-32.

Species: Liza tade

Head very short (19 to 23% of standard length; 23 to 25% in L. subviridis) and with distinctive bulge on sides; also caudal fin forked.

Species: Liza persia

Comer of mouth reaches to vertical from posterior nostril (to vertical from anterior nostril in L. subviridis).

Species: Valamugil speigleri

Adipose tissue covering eye except for pupil; upper lip fleshy, lower lip thin; posterior tip of upper jaw hidden when mouth closed; origin of second dorsal fin behind origin of anal fin; pectoral fin a little shorter than head length; with auxiliary scale almost half the length of fin; caudal fin forked; scales In lateral series 37 to 40.

Order: Pleuronectiformes

Family: Cynoglossidae

Flat fishes; dorsal originates on head; dorsal and anal confluent with caudal.

Species: Cyanoglossus cyanoglossus

D. 98-106; A. 78-83; L. lat. 80-89; rostral hook short, not extending behind eye; angle of mouth nearer end of snout than gill opening.

Species: Cyanoglossus lida

D. 99-112; A. 75-87; L. lat. 82-95; angle of mouth nearer gill opening than end of snouth; rostral hook extending to below lower eye.

Order: Polynemiformes

Family: Polynemidae

With two dorsal fins; mouth below snout; adipose eyelids present; pectoral fin in two parts.

Species: Eleutheronema tetradactylum

D. VIII; I-II, 13-15; A. II, 15-17; P. (16-17) +4; L. lat. 78-80; Tr. (9-10) + (13-14); upper lip absent, lower developed in angle of mouth; anal originates opposite second dorsal; upper pectoral filament reaches just beyond ventral origin.

Species: Polynemus indicus

D. VIII: I; 13-14; A. II-III, 11-12; P. (2-3) + (12) + 5; L. lat. 70-75; Tr. 7 + (12-13); first 2-3 pectoral rays simple, remainder branched; pectoral filaments reach almost to anal origin; second dorsal orginates in front of anal.

Family: Harpadontidae

Elongate with adipose fin and trilobed caudal fin; head short, with very short, rounded snout, pectoral fin longer than head.

Species: Harpodon nehareus

Eye small; mouth very wide, armed with slenders, recurved and depressible teeth of unequal size, lower jaw longer than upper; pelvic fin very long.

Order: Mastacembeliformes

Family: Mastacembelidae

Dorsal, caudal and anal fins confluent; some free spines before dorsal; anal with 3 spines; no ventral fin; mouth bordered by premaxillaries only.

Species: Macrognathus aculeatus

D. XIII-XVII; 50-54; A. II-III, 50-52; P. 22-25; upper surface of head and snout without scales; 19-23 scales between lateral line and origin of sort dorsal; posterior spines longer than anterior spines; head scales larger than body scales.

Order: Tradontiformes

Family: Tetradontidae

Two lateral lines, upper not reaching end of tail and meeting the lower above anal fin.

Species: Tetradon patoca

D. 9-11; A. 8-10; depth 31/2 without caudal; whole of back to dorsal origin and belly spiny; single nostril with raised margin; interorbital broad; caudal dark distally.

The following authors were consulted: Ahmed (1984); Khan (1991); Mohi (1977); Munro (1982); Oren (1982) and Zafar (1992).

IDENTIFYING KEY TO ZOOPLANKTON

Every major group of animals has its representative in the zooplankton either as adult or as larvae. So the following key has been made for group identification of the zooplankton community:

1. Radially o biradially symmetrical forms......................................................................... 2
Bilaterally symmetrical forms or asymmetrical............................................................... 3

2. Usually radially symmetrical forms, sometimes forming complicated colonies of individuals; diploblastic................................................ Phylum: Coelenterata

Biradially symmetrical forms with eight rows of ciliary combs arranged the length of the body....... Phylum: Ctenophora

3. With a vertebral column or a notochord or both................................ Phylum: Chordata

With neither a vertebral column nor a notochord.......................................................... 6

4. With a vertebral column........................................................... Sub-Phylum: Vertebrata

With a notochord only..................................................... 5

5. Notochord confined to the tail region only................................ Sub-Phylum: Urochodata

Notochord extends whole length of the body................. Sub-Phylum: Cephalochordata

6. With a well-developed external skeleton and with segmented appendages......... Phylum: Arthropoda...... 7

Without segmented appendages................................................................................ 18

7. Carapace forming a bivalved shell covering the entire body........................................ 8

Carapace not such like............................................................................................... 9

8. With a well-developed cement gland at the anterior end.............. Sub-Class: Cirripedia (Cypris larvae) (Nauplius with two spines on antero-lateral comers of the carapace)

Without a well-developed cement gland; second antennae larger.......................... Sub-class: Ostracoda

9. Three pairs of segmented appendages.................. Class: Crustacea (Nauplius larvae)

With more than three pairs of appendages................................................................. 10

10. Carapace forming a bivalved shell which does not cover the head.... Order: Cladocera

Carapace not such like.............. 11

11. With a carapace covering part or all of the thoracic segments................................... 12

Without a carapace..................................................................................................... 16

12. Some of the thoracic appendages uniramous............................................................ 13

All thoracic appendages biramous ........................................................................ 14

13. With two pairs of well-developed thoracic appendages, the second developed to form a large raptorial claw....................... Order: Stomatopoda

With eight pans of thoracic appendages, of which last five pairs uniramous................. Order: Decapoda

14. Carapace small, not covering the last five thoracic segments......................... Order: Cumacea

15. Carapace fused with all thoracic segments, thoracic gills present, not covered by the carapace........... Order: Euphausiacea

Carapace fused only with the first three thoracic segments; thoracic gills, if present, covered by the carapace...................... Order: Mysidacea

16. Most of the thoracic appendages uniramous and leg-like............................................ 17

Most of the thoracic appendages biramous and swimmeret like................... Sub-Class: Copepoda

17. Thoracic legs all of one kind; body usually flattened dorsoventrally.................... Order: Isopoda

Thoracic legs of more than one kind; body usually flattened laterally...................... Order: Amphipoda

18. Body barral-shaped and transparent; conspicuous rings of muscle in body wall....... Sub-Phylum: Urochordata

Body not such like...................................................................................................... 19

19. Body with paired lateral setae........................Phylum: Annelida. Sub-class: Polychaeta if present, setae not paired and lateral....................... 20

20. With exoskeleton or lorica.......................................................................................... 21

Soft-bodied, without exoskeleton................................................................................ 25

21. Body clearly segmented, worm-like........................... Class: Insecta (Larvae of Diptera)

Body not segmented........................................................................................ 22

22. With a bivalved shell covering all or most of the body................................................ 23

Not such like..........................................................................................24

23. With a lophophore........................................................ Phylum: Brachiopoda

Without a lophophore.................................. Phylum: Mollusca (Class: Pelecypoda)

24. Body with a cup-shaped univalve shell............. Phylum: Mollusca (Class: Gastropoda)

Body win a lorica which does not form a cup as above; cilia of a corona surrounding the mouth........................................ Phylum: Rotifera

25. Larval forms, with one or more bands of cilia encircling the body.............................. 26

Larval forms and adult not as above....................................... 28

26. Ciliated bands (Prototrouch) simple.......... Trochophores (Phyla: Annelida & Mollusca)

Ciliated bands not thus............................................... 27

27. Ciliated band forming two lateral lappets................ Pilidium larvae (Phylum: Nemertea)

Ciliated band forming eight median lobes, flattened leaf like forms....... Muller's larvae (Phylum: Platyhelminthes)

Ciliated band forming several median tentacles............... Actinotroch larvae (Phylum: Phoronidea)

28. Larval forms, with more or less complicated ciliated band around the mouth, and with a second band anterior to mouth................................................. Phylum: Echinodermata

Adults, nor with the above characteristics.................................................................. 29

29. Body cylindrical and worm like, with no trace of segmentation, with no well-developed head...................................................................................... Phylum: Nemathelminthes

Body elongate, with paired lateral fins, with strongly developed chitinous jaws laterally on the head................................................................................ Phylum: Chaetognatha

The following authors were consulted: Davis (1955); Newell and Newell (1963) and Wickstead(1965).