In natural waters in the case of many fish species, only few percentage of released eggs can reach the fingerling size. Rough environmental conditions, predatory plankton, insects, fish, frogs, snakes, birds etc. reduce the survivality of fish seed. Contrary to this, 20-70 percent of eggs bred artificially can grow up to that size, if appropriate management methods of incubation, fry and fingerling rearing are applied. As survivality of progeny depends mainly on management, quantity and quality of produced eggs depends primarily on quality of broodfish.
Time requirement for carps to attain sexual maturity, and average weight of just matured fish in Bangladesh are given in Table 2.
Young immature broodfish, also called “broodfish candidates” are usually selected from market size fish. Market size fish population available for selection of broodfish candidates should be healthy, uniform in size and well developed. Population consisting of fish of different age and size or produced in strongly overstocked/underfed pond are not suitable for selection. Selected fish must be reared in well managed fish ponds where standing crop of fish does not exceed 1.6-2.0 ton/ha.
To avoid difficulties of using broodfish of too big size, yearly recruitment rate of population should be 25–30%. The broodfish candidates may be stocked in those ponds where matured broodfish are kept in off season period. As feed requirement of broodfish candidates is different, market size fish ponds are not suitable for rearing broodfish candidates.
Ponds with large water surface area and water depth of at least 1.5 m are best for broodfish candidates. Stocking ratio of different species should be in accordance with the general principle of stocking of polyculture ponds. Filter feeders should not exceed 35–40% and in it the ratio of zooplankton consumers (catla, bighead) should remain under 30%.
Age and weight of broodfish at first breeding
Broodfish requirement of hatcheries/fish seed production farms should be determined by egg production capacity of individual broodfish, and survival of embryos and fries. For fertilization of eggs of 1 female, 1 male is used, so total broodfish requirement is about two times the female fish requirement. Egg production capacity of different species, survival of egg/fry in hatcheries, survival during nursing and fingerling production using different management systems are given in Table 3.
DATA FOR CALCULATION OF BROODFISH REQUIREMENT
|Species||Egg production of one female|
|Number of seed in traditional technology||No. of fingerlings in improved methodology|
* All the data are higher 20% if improved the method of broodfish management isapplied.
Size, location and stocking of broodfish pond
Broodfish rearing ponds should not be far from the hatchery to avoid long transport. The ponds used for maintaining and preparation of broodfish should be fertile and deep, having at least 1.5 m water depth in dry season. Water replenishment devices (shallow or deep tube well or stream) should be available for water supply as and when necessary. Considering importance of natural food in the diet of broodfish, bigger size ponds with low stocking density (not exceeding 1.6–2.0 t/ha) are most suitable.
Broodfish ready for breeding should certainly be kept in ponds located near the hatchery. Considering the fact that broodfish are frequently seined in this ponds, the most suitable size of a broodfish pond is 0.1-0.2 ha, and its width should not be more than 25–30 m to facilitate netting.
Since those ponds are used for keeping “ready” broodfish, stocking density may be as high as 2.5–3.0 t/ha. Stocking ratios maintained by leading fish farmers in Bangladesh are given in Table 4.
The advantage of polyculture stocking of broodfish is that different fish species in reasonable ratio utilizes all types of natural food produced and it improves food supply of fish. However, some practical problems may emerge in this management system, because all species are caught during netting. To avoid these difficulties, monocultural or bicultural stocking is used in some hatcheries to facilitate good broodfish management.
Female and male broodfish are used in 1:1 ratio in artificial breeding. Consequently, about 50% of broodfish population is male. As male fish are not so vulnerable to overstocking, in hatcheries having no sufficient number/size of ponds, separate stocking of male fish in high density renders possible lower stocking of females. But keeping catla males in overstocked ponds is not recommended.
As mirror/common carps breed in ponds in presence of breeding substrate, especially when rain starts, separation of the two sexes is recommended.
STOCKING RATIO OF BROODFISH USED BY FISH SEED PRODUCERS IN BANGLADESH
|SPECIES||COMPOSITION OF DIFFERENT STOCKING TYPES (%)|
* Not more than 300 kg/bigha (1335 m2).
Preparation and manuring of broodfish ponds
As food supply of fish depends mainly on natural production of ponds, presence of unwanted wild fish in ponds hampers broodfish management. As a consequence of uncontrolled reproduction of this weed fish, dense population may develop and can consume significant percentage of natural food organisms. Therefore to eradicate wild fish, broodfish rearing ponds should be dewatered/poisoned. (Methods are detailed in Section 2.4.1.) After dewatering or few days after poisoning, lime (CaO) should be spread/sprinkled on bottom/water surface at the rate of 500-700 kg/ha.
To produce dense population of natural food organisms, application of 2-5 ton/ha organic manure, 15–20 kg/ha urea and 5–10 kg/ha triple superphosphate is recommended. Manure should be applied after partial replenishment of water if the pond is dewatered. During broodfish rearing, for maintenance of plankton population, daily application of small doses of manure is suggested (50-60 kg/ha organic manure mixed with 1-2 kg/ha inorganic fertilizers). If such daily manuring becomes difficult, application of 200 kg/ha poultry drops or rumen content of slaughtered ruminants or 300 kg/ha cowdung supplemented with 5-7 kg inorganic fertilizers in every 4th-5th day, is recommended.
During both pond preparation and rearing, frequent raking of pond bottom is essential to prevent development of anaerobic environment in upper layer of mud.
Feeding of broodfish
Generally broodfish requires the same quality of feed as fingerling. Considering availability of feed ingredients, examples of three types of artificial feeds, recommended for broodfish, are given in Table 5.
COMPOSITION OF DIFFERENT TYPES OF BROODFISH FEEDS
|INGREDIENTS (%)||FEED TYPES|
|Mustard oil cake||20||20||32||20|
As there exist growth inhibitor in mustard oil cake and quality of its protein is poor, feeding fresh powdered mustard oil cake must be avoided. It may be used either water-soaked or after a few hours storage in wet dough mixed with feed ingredients such as cattle blood or ground duckweed.
Some farmers use mixture of 50% rice and 50% wheat bran in off season (from September to December) for feeding broodfish. This method is appropriate when ponds are not overstocked and frequent manuring is carried out. In the situation where stocking is high (above 2 ton/ha) this method is not suitable.
Feed ration should be 1–2 percent (dry weight) of body weight in cold period and 2–3 percent after it. (Wet feed rations should be higher according to wet content.)
Specific features of fish species must be considered at feeding of broodfish:
For silver carp blooming of algal plankton or blooming of Paramecium/ratifera population should be maintained with frequent manuring. Rumen content is a very good fertilizer for this species. Silver carp can filter soaked particle of wheat bran, rice polish and mustard oil cake also.
Gonad development of rohu and mrigal is fast, if ground duckweed and fish meal are mixed with traditional feed ingredients, i.e. rice/wheat bran and mustard oil cake.
Floating duck weed and other fresh (not withered or dry) green plants such as grass, banana leaves, napier grass etc. can accelerate gonad development of grass carp. Considering the feeding habit of grass carp, use of floating feeding frame is highly recommended instead of spreading green material on whole surface of the pond.
Though catla can consume artificial feeds in addition to zooplankton, it can not replenish the natural food, so low stocking density of other zooplankton feeder fish (first of all bighead carp) is recommended to avoid food competition.
Using of animal-origin materials (slaughterhouse waste, blood or fish meal) is essential for preparation of mirror/common carp broodfish, reared in ponds with high stocking density.
Germinated seeds, chopped snails and silkworm pupae are excellent feeds for carp broodfish.
Different types of carp hatcheries have been developed. Few of them are very simple and give limited advantages compared to semi-natural breeding of fish. Others are sophisticated, requiring high investment and running cost. Hatcheries in Bangladesh combine some advantages of sophisticated fish hatcheries with low investment and running cost.
Four main units of carp hatcheries are:
Water supply system
Pond water suitable for carp culture is also appropriate for keeping broodfish in hatcheries after hypophization till stripping. However, high temperature (above 30°C) and low oxygen content of pond water in dark period, may hamper ovulation. Use of cool well water, aerated properly, helps to avoid such difficulties. Moreover, it is easy to recognize ovulation in tanks with clear well water. Considering increased oxygen demand of broodfish after pituitary treatment, flow in the broodfish tanks of at least 1-1.5 liter water/minute/kg broodfish is necessary. Water supply can be decreased by aeration, but for removing metabolites at least 0.5 liter water/minute/kg is necessary.
For large scale incubation and keeping larvae untreated, pond water is not suitable. Presence of colloids, plankton (first of all Cyclops which may attack egg shell and newly hatched fry) and high fluctuation of oxygen, hamper fry production. Higher temperature causes blooming of bacteria, increase in oxygen requirement and metabolite production of fry, deteriorating the environment. To improve those conditions in hatcheries supplied with pond water, pebble filters can be used (Figure 1). Ponds used for hatchery supply of water must be deep enough to avoid increased water temperature. Bottom condition of such ponds should be properly maintained and for that purpose the ponds should be kept dry in off season. Stocking of silver carp, grass carp and catla in low density (total biomass should not exceed 1.0–1.5 t/ha) helps maintaining good water quality. However, the most appropriate measure is to establish hatcheries in those areas where there is arrangement for shallow or deep tube well water supply.
In majority of fish hatcheries in Bangladesh, well water contains high iron level while oxygen content is low. Intensive aeration using perforated trays arranged in vertical row and sedimentation of precipitated iron, helps to eliminate harmful effect of iron (Figure 2). Water quality suitable for incubation and keeping of larvae is given in Table 6.
WATER QUALITY REQUIREMENT OF CATFISH HATCHERIES
(AFTER TUCKER, 1988 IN BODY, 1990)
|Chemical and physical feature||Desired level|
|Total dissolved gases||105%|
|Dissolved oxygen||min. 6 mg/liter|
|Carbon dioxide||max. 10 mg/liter|
|Calcium hardness||min. 20 mg/liter as CaCO3|
|Ammonia (Un-ionized)||max.0.05 mg/liter|
Pebble filter suitable for fish hatcheries
(Modified after Woynarovich and Horvath, 1980)
Device suitable for aeration of well water in hatcheries
Water current during incubation should be adjusted to water requirement of different incubators and oxygen requirement of eggs and fry. Stable hydrostatic pressure of water is essential. To facilitate it, overhead tank should be used in hatcheries. For avoiding frequent change in water pressure, overhead tanks should contain huge quantity of water. Flat overhead tanks with large base area are more suitable for keeping constant water pressure than deep tanks, containing same quantity of water. Tanks containing large quantity of water are recommended for hatchery, as they can ensure water supply for a longer time even after power failure.
In spite of strong water current in overhead tanks, filamentous algae may develop and adhere to the tank walls. Metabolites of algae may unnecessarily load the hatchery water. Moreover, bacterial decomposition of dead algae may prove poisonous. To avoid development of algal carpet, tanks should be covered to prevent light penetration.
Living organisms, partially decomposed organic materials and inorganic sediments can accumulate in water pipes of fish hatcheries. They deteriorate water quality. Mere disinfection of water pipes is not the adequate measure for their elimination. Water pipes should be opened after season and cleaned mechanically. in addition to disinfection.
All arrangements, containing appropriate quantity of water and having sufficient water supply are suitable for keeping broodfish in hatcheries between injection and stripping or spawning. Rectangular tanks with one water inlet, or circular cement tanks with sideways -directed inlets and centrally located outlet are used for broodfish manipulation in Bangladesh. Merit of rectangular tank is that it is easier to catch broodfish for injection and stripping. However, the stronger water current that may be created in circular tanks has positive effect on ovulation of those species which spawn in rivers. Tanks should be located under shade to avoid strong light stressing fish. Walls of tank should be smooth, otherwise fish will be wounded. Tanks should be covered with net or deep enough to prevent broodfish from jumping out. Water depth more than 60-80 cm in tanks is not necessary unless semi-natural spawning of Indian carps is carried out. Circular tanks bottom should have little slope toward the center of tank where water outlet is installed. Water outlet of tanks should be covered by iron grill to prevent penetration of accidentally dead fish into water outlet. (It is not recommended if tanks are used for semi artificial spawning.) Water outlet should be suitable for maintaining different water depths in tank and for quick decreasing of water level to facilitate manipulation of broodfish (Figure 3). Circular spawning tank has direct connection with circular incubators. Water current can wash out spawned and fertilized eggs to incubators.
Water outlet of broodfish tanks
Loading of tanks depends on water supply. It ranges 5–10 kg/m3. Water supply requirement of 1 kg broodfish is 1-1.5 liter/minute. However, extremely strong current forcing fish for quick swimming is not recommended.
Circular incubators of 3–4 m diameter are used also for spawning Indian carps. Recommended loading rate of tanks is 20–25 kg broodfish. Broodfish must be removed from tank after spawning and remaining eggs may be incubated in tanks. Though, considering volume and water supply of such tanks more fish can be spawned there, it is not reasonable to stock more to avoid overloading of tanks by eggs.
Circular cement tanks are used for incubation of floating eggs of Chinese and Indian carps and “funnel-type” or jar type incubators for mirror and common carp. Funnel and jar type incubators are suitable for incubation of small quantity of floating eggs, but incubation of mirror carp eggs in circular type incubators is impossible.
Circular tanks of about 3–4 m diameter and 1–1.5 meter water depth are used. Duck beak type water inlets (ejectors) are located at the bottom of tanks connected to a central water supply ring built in the bottom. Distance between the ejectors is 60-80 cm. Direction of ejectors may be changed. Cylinder type filter with about 1.0–1.5 m dia is built up in the center of the tank. Shell of cylinder is made of concrete and superficies is covered with fine meshed size net to prevent fry from escaping. Mesh size should range between 0.3–0.4mm. If mesh size is too small, it hampers water penetration. Fry can escape through a net with mesh size larger than 0.4 mm, or it gets stuck in.
Circular spawning tank with 7.5 m3 water volume should be loaded with about 500 eggs/liter, which is equivalent to about 3.5–4.0 kg dry Chinese or Indian major carp eggs. Maximum water flow requirement of this incubator is about 3 m3/hours (3000 liter).
Main demerits of a circular incubator is that its central cylinder has limited filter-surface, because concrete supports of filter of water outlet occupy a significant part of the surface of superficies. The clogging of filter may be frequent at the time of hatching. The clogging may be avoided by using circular incubator as developed by Mr. D. Mohosin, Manager of Rajshahi fish Seed Multiplication farm. This incubator by its shape is similar to circular spawning tanks having slight slope towards the center. Volume of tank is about 7 m3. Tank is supplied with water from a ring prepared by water pipe located about 50 cm from the wall of tank. Duck-bill type ejectors are installed on the ring at distances of 40–50 cm. They may be turned to any direction as required. The ring is removable from the tank. Central water outlet cylinder is also removable. It is made of iron bars and the iron shell is covered with copper sieve used as filter for shallow tube wells in the country. When cylinder is installed, a strip of rubber foam should be put under the bottom-ring of superficies for keeping the eggs back and preventing fry from escaping. If arrangement of water ejectors is proper (every second is directed with small angle to wall and the others to superficies of central cylinder) floating eggs do not rub against wall of tank and filter-surface (Figure 4).
“Funnel type” incubators made of concrete with different water volumes are also used. Actually, they are not funnel type, although this name is used in Bangladesh. This incubator consists of a cylindrical shape upper portion and a funnel shape bottom. Diameter of cylinder varies from 50 to 70 cm, height is 50– 60 cm. Total depth of incubator is 80-120 cm. Fine meshed size sieve is fixed to upper portion of the funnel to keep back larvae from escaping (Figure 5). Loading of such incubators is about 1000-2000 egg/liter and fry production is about 1 kg. Water requirement of incubators is about 10-15 liter/minute (0.6-1.0 m3/hour).
The funnel type incubators have no proper shape in several fish hatcheries in Bangladesh. Instead of a funnel, lower portion of incubator is a hemisphere. It is not entirely appropriate for incubation of floating eggs and not suitable for heavy eggs of mirror/common carp, because water is stagnant in hemisphere and eggs can not remain in floating condition. This sedimented eggs suffer from depletion of oxygen and may die.
Zouger-jar type incubators with water capacity of about 8–15 liter are also used in a few fish hatcheries. Water requirement of a jar is about 2–3 liter/ minute, loading capacity is 30–50 g dry eggs of Chinese or Indian carps and 300–400 g mirror/common carp eggs.
Larva holding tanks and installations
for collection and packing of larvae
Incubators, except smaller volume jar type incubators, are suitable for hatching larvae and keeping newly hatched fry. Most comfortable method is using incubators both for incubation and keeping of larvae.
Advantage of big size funnel type incubators is that, healthy, newly hatched fry can swim out by water current, while deformed embryos remain there.
Fry, before development of swim bladder must be kept in incubators supplied with water current. After that hapas installed in rectangular cement tanks are suitable also for keeping fry. Water should be sprinkled on hapa for supplying larvae with oxygen rich water. Loading of hapas is 250–300 g swimming fry for 24– 48 hours.
In hatcheries, a space for packing and storing larvae filled bags under shade should be maintained. Its floor should be smooth for avoiding puncture of plastic bags.
Circular hatchery developed in Rajshahi FSMF
Funnel type incubator
Breeding period of carps is shown in Table 7. It is possible to breed carps at least two times, it may be even three times in one breeding season. As gonad development depends on quality and quantity of food, stripped fish should be kept in excellent condition for selection in repeated breeding.
As cultured carps are river-origin, their breeding temperature is lower than that prevails in fish pond in breeding season. Range of acceptable temperature for artificial breeding is 22–30 C, the optimal being 25–27 C. Well water is necessary to get optimal temperature of water in peak season.
Fish for artificial breeding are selected by visual examination. Main criteria of selection of female and male broodfish are given in Table 8.
Selection of fish is more difficult if the fish population is used for second reproduction within the same season. Sometimes bulgy belly may be due to fat deposition and genital opening of fish stripped not long ago may also be reddish. However, considering all the criteria mentioned in Table 8 selection of suitable fish for breeding is not difficult. Fish having some, but not excellent belly at second reproduction usually gives good quality eggs, though quantity is less. Only the excellent grass carp females should be selected for second reproduction. Contrary to other species, grass carp females of mid-quality will not give good eggs in this time. Latency time at this grass carp females is longer with 2.0-2.5 hours than at good fish.
Ovary of females has significant weight and it is not fixed firmly in body cavity. Mechanical effects (for example jumping of fish or throwing of fish at selection, falling them on floor at manipulation) can cause injuries which may hamper ovulation. As gentle manipulation of broodfish as much as possible is essential. Restless jumping at the time of selection of broodfish from pond is unavoidable. However, selected fish must be transferred to hatchery in special bags or broodfish scoopnets or “hammocks” (Figure 6). Scoopents or small pieces of knot-free nets are recommended for broodfish manipulation in hatcheries.
BREEDING PERIOD OF CARPS
Devices for short transportation of broodfish
SELECTION CRITERIA FOR FEMALE AND MALE FISH
|Fins, skin||Surface of pectoral fins is smooth. First rays are not very thick. Skin of head is smooth also.||First ray of pectoral fins is thick. Inner surface of pectoral fins is rough. Skin of head is rough sometime.|
|Abdomen||Belly of female fish ready for breeding bulges. Bulge extends from pectoral fins to genital opening. It is soft and the median ridge is not significant.||Belly of male fish is not bigger than before season. It is hard and the ridge is well expressed.|
|Genital opening (It is located before anus)||Genital opening is swollen, sometimes protruding. Color is reddish.||Genital opening is not protruding.|
|Sexual products||It is strictly forbidden to press out eggs from ovary for checking its condition.||Whitish milt may be pressed out with gentle stripping of male fish. (Sometimes catla males do not give milt without hormone injection.)|
Several techniques of hormone administration have been developed for Cyprinids. Hormone materials diluted in 1–3 ml water or physiologically balanced solution are injected in muscle or in body cavity or nearby the heart of fish. Though each method has some advantages and disadvantages, no difference in efficiency was found in them. However, administration of diluted hormones at the base of pectoral fin is most comfortable, if no tranquilizers are used.
Dry pituitary gland should be powdered in mortar before dissolving it for injection. Tissue homogenizator is recommended for processing PG stored in alcohol or in acetone.
There are controversies about hormone doses and protocol of injection. Using mirror/common carp PG dried in acetone and preserved in desiccator 0.35–0.45 mg/kg as a preparatory dose and 3.5–5.0 mg/kg as decisive dose is effective on the majority of fish, administering two doses by 6-8 hours gap.
PG dose of male fish is 1.5-2.0 mg/kg. Time of injection coincides with second dose of female fish. It may be also administered between the time of first and second injection of females.
Majority of relevant literature suggests higher doses for induction of ovulation, 6-12 mg in the case of two injections, using about 30% of total dose as preliminary one. Difference between unit weight of PG treated with alcohol or acetone and further the effect of preservation on unit weight of PG may be the main reason of this contradictions (Table 9). Moreover, PG of Indian major carps contains less gonadotroph hormone in unit weight than PG of mirror carp. However, fish are extremely flexible, different doses, different ratio of first and second doses, different protocol of injection may be suitable for inducing ovulation of well prepared females.
WEIGHT OF PITUITARY GLAND PRESERVED IN ALCOHOL AND ACETONE AFTER DRYING
|Preservative||M E A S U R I N G T I M E|
|Alcohol||7 mg||--||5 mg||--||1.5 mg|
|Acetone||13 mg||8 mg||--||4 mg||3.7 mg|
*: Kept in air;
**: Kept in desiccator
Fish culturists sometimes believe that there are some biological advantages in using HCG instead of (or with) PG for reproduction of Chinese carps. Such biological advantages of HCG administration on PG was not proved.
Hormone doses applied in Kotchadpur Fish Hatchery are given in Table 10. In other places fish farmers use other doses and schedule.
TABLE 10 HORMONE DOSES USED IN KOTCHADPUR FISH HATCHERY
|Species||Season||1st PG dose|
|2nd PG dose |
|Silver carp||E.S.||220 I.U./kg||8||1750–1800 |
4 mg/kg PG
(E.S. early season, mid March to end of April; M.S. mid-season, May; P.S is peak season, June-mid July)
30 I.U. of HCG is equal to 1 mg, (in case of “Sumach”) and 1 mg acetone dried mirror carp PG is equivalent to about 6–10 mg HCG.
For mirror/common carp and sharputi 0.35–0.4 mg/kg PG is recommended as first dose and 3.0–3.5 mg/kg as second dose, applied with 6 hours interval. Ovulation time is 5–6 hour after second dose.
Sometimes tranquilizers are used before injection and stripping of fish. Deep tranquilization of broodfish is discouraged, as in some species no ovulation occur after long and deep anesthesia. Low concentration of tranquilizer applied for short period, decreases activity of fish but it does not induce slumber condition and, therefore, does not disturb process of ovulation.
Ovulation is syncronic in majority of cultured carp species and releasing of eggs takes place in short time. Ovulation of mirror/common carp is a syncronic. It requires more time. Some percentage of eggs are released earlier than the main portion. However, it is not possible to start stripping immediately when ovulation starts, because only few drops of eggs can be stripped at this time. Gap between beginning of ovulation and mass ovulation is 15–20 minutes. To avoid losses as a consequence of spawning of fish in tanks, it is recommended to stitching the genital opening at the administration of second pituitary gland dose (Figure 7). If it is closed no losses occur and eggs released from their envelope in different time are stripped at the same time. Released eggs may remain for this short period in ovary without deterioration of quality.
Circular tank should be properly cleaned and filled with well water upto about 1 meter depth before releasing fish in it. Soon after stocking fish, water circulation must start and the tank must be covered by a net to avoid fish to jump out. It is recommended to keep fish in the tank for at least 5–7 hours to discharge their intestine before injection. Natural spawning usually starts 5–6 hours after second injection. After completing ovulation broodfish must be removed from tanks.
Stitching of genital opening of mirror carp
(Modified after Woynarovich and Horvath, 1980)
Ovulated egg looses its connection with blood vascular system which supplies oxygen when in ovary. So it should be stripped immediately, to avoid its deterioration by anoxia. The period of ovulated eggs stay in ovary without significant deterioration is short at fish with synchronic ovulation. It is essential to strip fish immediately after ovulation. For recognizing exact time of ovulation it is recommended that a few male fish be kept in group of females. It is easy to check fish and determine the proper time of its stripping. Fish usually starts to spawn in tank. Some eggs also are released. Ovulated eggs are not swollen, so they are either drifted to corners of rectangular tanks where water current is week, or are drifted to central water outlet of circular spawning tanks. Sweeping above the bottom of tanks by a scoopnet of small mesh size it is easy to check presence of ovulated eggs in a rectangular tank. Also it is easy to see eggs released in circular spawning tank keeping glass or carafe at outer end of water outlet. With the appearance of first bunch of eggs stripping should be started immediately. It is suggested that the quantity of stripped eggs be weighed for easy calculation of expected quantity of fry.
Threads should be removed from mirror/common carp before stripping. After it there is no differences between stripping this carp species and Indian or Chinese carps.
If broodfish population is not uniform, comprising of different age and size of broodfish or broodfish collected from different areas, ovulation time of broodfish may differ. Repeated testing of individuals, not releasing egg, is suggested for determining the time of ovulation.
It is a general rule that females should be dried up before stripping and eggs should be stripped in dry pots. It eggs contact water, swelling starts and micropyle closes quickly. Though blood droppings into stripped eggs will not cause swelling, it is suggested that before appearance of large quantity of blood stripping be stopped to take care of broodfish.
Quality of egg may be roughly forecasted at the stripping. If stripping is too late and eggs are overripe, quantity of ovarial fluid is high. Fertilization rate of such eggs is low.
Male fish should be stripped parallel with females or a bit earlier. It is essential to protect sperm from water (originated from body surface of fish or droppings from wet hand of fishermen). A few minutes retention in room temperature or for 0.5–2.0 hours in refrigerator at 5–8°C does not decrease viability of sperm.
At least 5 ml. preferably 8–10 ml of sperm should be used for fertilization of 1 kg egg. Egg and sperm should be mixed in dry condition using dry feather or plastic spoon. For fertilization of non-sticky eggs of Chinese and Indian carps water may be poured on the mixture at a proportion of 10 percent of total quantity of egg. Fertilization takes place within about 25–40 seconds. After that eggs should be continuously stirred (but not too strongly) and some more water need to be added to the swelling eggs. Fertilized eggs should be poured in funnel type hatchery units within 3–4 minutes and within 10 minutes into circular incubators.
Suspension of milk powder (100 g milk powder and 10 g kitchen salt suspended/ diluted in 10 liter of water) or solution of 40 g kitchen salt and 30 g urea/10 liter water is required for fertilization and treatment of mirror/common carp eggs. After fertilization, 1.5–2.0 hours gentle stirring of eggs is necessary for eliminating stickiness of eggs, if milk powder is used. Use of urea/salt solution for 1.0 hour followed by treatment of eggs with milk powder suspension for 10–15 minutes is suitable for elimination of stickiness. It is suggested to test if stickiness was eliminated before pouring eggs into incubators. Some eggs should be put in a glass containing water and should be stirred. If eggs stick to each other or to bottom of glass more treatment is necessary. If stickiness is eliminated, eggs used in test are found drifting with water. If eggs are poured very early in incubators, bunches of eggs will develop and oxygen supply of eggs inside will be inadequate. As a consequence of it, rate of mortality will be higher.
A significant quantity of water is absorbed by fertilized eggs. Though major portion of water penetrates in egg within 1.0–1.5 hours after fertilization, egg reach final size 2–3 hours later.
Length of embryonic development depends on species and water temperature. To some extent, it is determined by oxygen content of water also. Low oxygen concentration during incubation increases duration of embryonic development. If oxygen concentration is appropriate during incubation but low before hatching, hatching takes place earlier. Duration of embryonic development of carps is 20– 26 hours at 27–29°C water temperature.
Oxygen requirement of developing embryos increases from fertilization to hatching. At the beginning, oxygen requirement is low, so water current (quantity used for running hatchery units per minute) should be low. Strong current is not necessary. Moreover, it may be harmful to eggs containing big, loose embryonic cells. Later, from about 6–8 hours after fertilization, oxygen requirement increases. Strong current is not harmful on embryos at this time. As a consequence, water supply of incubators should be increased slowly to the maximum (mentioned in Section 2.2.1).
Fertilization rate of egg usually ranges 60–85%. Percentage of deformed embryos is about 1–3% in main season and 2–5% in late season. It is essential to remove bad eggs by syphoning from jar or funnel type incubators, or with trapping from circular type incubators after hatching (Figure 8).
A significant decrease or stopping of water supply just before hatching will induce and synchronize hatching of fry. However a delay of water supply longer than 5–7 minutes may be harmful. If hatching of embryos is synchronized by stopping water current, biochemical elimination of empty egg shell by “hatching enzyme” is more effective.
Some parasites and bacteria may develop on the shell of developing eggs. Saprolegnia infection is usually not strong in temperature above 25°C, unless huge quantity of dead eggs are kept in incubator. Organic loading of hatchery water facilitates mass reproduction of bacteria on the surface of eggs. In extreme cases, bacteria can make the egg shell week causing too early hatching of embryos. Such embryos are not protected from further infection, so they can not survive.
For disinfection of eggs at least two treatment is recommended, one after total swelling and the other 6–7 hours before hatching. However, in waters loaded with organic materials, more frequent treatment is necessary. Treatments should be done in incubators supplied with running water. Chemicals suitable for treatment, suggested frequency and concentration of treatment are given in Table 11.
CHEMICALS RECOMMENDED FOR EGG TREATMENT
|Name of chemicals||Suggested concentration||Frequency of treatment|
|Malachite green||5 ppm (5g/m3)||1, after swelling|
|Formalin||1:10 000; 1:5000||In every 3–5 hours|
|Methylene blue||0.1–0.2 ppm||2–3|
|Potassium permanganate||5 ppm||2|
Syphoning/trapping of bad eggs from different incubators
(Modified after Woynarovich and Horvath, 1980)
Hatched out larvae are mixed with empty egg shell in incubators after hatching. Egg shells can create problem with clogging of filter of water outlet. Continuous cleaning of filter is essential after hatching. Small mesh size net fixed perpendicularly on water current of circular tanks are suitable to collect and remove majority of empty egg shells and unfertilized eggs (See Figure 8). Activity of enzyme produced by hatching larvae and mechanical effect of water current eliminate egg shells soon.
Larvae of Indian and Chinese carps are active after hatching. They swim up vertically and sink back and in the meantime they are drifted by water current. Only the healthy larvae can swim up, so they may be drifted out from incubators by overflowing water. This facilitates separation of healthy larvae from deformed ones and from debris accumulated during incubation.
Larvae of mirror/common carps have a special organ producing sticky excreta capable of sticking larvae to surface. However, if sufficient surface is not available (for example in “funnel type” incubators) they gather near the center of incubator and are drifted passively by water. Strong current of water may be harmful. Current should keep gathered larvae in floating condition near the water inlet of jar. Strong current scatters larvae in incubator which is not appropriate.
Oxygen requirement of newly hatched fry is high. Only saturated water is suitable for supplying fry.
Aquatic insects and some zooplanktons such as Cyclops, are harmful to fry. If pond water is used for hatchery supply, elimination of Cyclops using organophosphates is essential. Moreover, in water containing higher quantity of organic material, frequent formalin treatment is recommended with the concentration of 1:10 000, treating fish in current water in every consecutive 2–4 hours. It is not easy to develop uniform concentration in big circular tanks. Instead of sprinkling over concentrated formalin on water surface it should be syphoned into tank slowly (Figure 9).
The length of time during which larvae do not take food is 1.5–2.0 days. Mouth of fry is activated and swim bladder develops at the end of this period. After it, fry can control their swimming and are capable of searching food.
Appropriate method for formalin treatment of circular tanks
Fry have some yolk at the beginning of this period, though they are ready to prey small zooplankton organisms. Best food organisms for newly hatched fry are the big size protozoans and ratiferas. Instead of keeping them in hatcheries in overcrowded conditions it is strongly recommended to stock fry as soon as possible in well prepared ponds. However, sometimes immediate stocking of fry after development of swim bladder is not possible. Again, collection of sufficient quantity of ratiferas is also impossible. In such a case, yolk of hard-boiled chicken egg is used for feeding larvae in hatcheries. This feed is not natural and feeding of fry longer than 1–2 days with it is not encouraged. Moreover, overfeeding must be avoided, because bacterial decomposition of accumulated egg yolk starts quickly destroying water quality. Unit weight of feeding fry is given in Table 12.
Fry kept in hatchery for long, become week soon and parasites (mainly protozoa) may infect them. Sometimes mass mortality occurs in hatcheries and survival in fish ponds becomes low as a consequence of unsuitable condition prevailing in hatchery.
NUMBER OF FEEDING FRY (IN UNIT WEIGHT)
|Species||Number of fry in 1.0 g|
For mass production of pre-nursed fry (“dhani”) or nursed fry the most productive and cheap way is pond nursing. There is no big difference between production methodology of prenursed fry and nursed fry, only stocking densities and lengths of rearing differ.
Shallow ponds, preferable with an arrangements of drainage are suitable for pond nursing. A pond not exceeding one bigha in size is the most appropriate one. Newly excavated ponds with clayey soil are not suitable, as the elimination of turbidity to facilitate light penetration takes long time. Of course those old ponds of clayey areas where pond bottom is covered with accumulated organic materials are suitable.
For satisfactory survival in ponds, special pre-and post-stocking treatments are necessary. Following steps are to be taken in pre-stocking management:
Population of unwanted fish must be eradicated from the pond either by dewatering or using fish poisons;
Process of decomposition of organic materials in pond bottom should be promoted with aeration of upper layer of pond soil. This process should be accelerated with repeated raking of inundated soil or by keeping the pond in dry condition for a short period;
Liming of pond;
Partial refilling of pond and management of plankton population; and
Eradication of water insects.
Important steps of post-stocking management:
Maintenance of productivity of pond ecosystem;
Controlling predators; and
Feeding of fish.
The fish that remains in pond after harvesting (regardless whether they are cultured or wild species) are harmful for new stock. They may be sources of fish diseases. They consume newly hatched fry reducing survival and competitors of food of young population. If ponds are kept in dry condition for a few days, these weed fish can not survive. Moreover, decomposition process of partially degradated organic materials is facilitated when pond bottom has a direct contact with air and gas accumulated in the upper layer of pond bottom escapes into air.
If there is no way of dewatering the pond fully, unwanted fish and other organisms (for example crustaceans) are to be eliminated by applying poison before new stocking. Three different materials are used for elimination of weed fish in Bangladesh. They are Rotenone, Phostoxin and Thiodin.
The most effective fish poison free from risk of secondary or side-effect is Rotenone. Effective dose of Rotenone is 2–3 mg/liter (2.7–4.0 kg/bigha at 1 m water depth). Residual effect of Rotenone lasts for 6–7 days in this temperature. Fish killed with Rotenone are fit for human consumption.
The other fish poison widely used in Bangladesh is the Phostoxin. It is harmful not only to fish, but also to other organisms including human beings. Gas developed from tablets is harmful on lungs. So, in using Phostoxin wind direction is to be considered. Suggested concentration of this material for fish poisoning is 0.25–0.30 mg/liter (0.25–0.30 g/m3, 340–400 g/ bigha) at 1 m water depth. (Considering that one tablet is 3 g, requirement of 1 bigha pond with 1 m water depth is 114–135 tablets.) Regular raking (using “horra”) is suggested after the administration of tablets for promotion of proper mixing of developing gas with pond water. Netting in this period is not recommended, as net can concentrate distributed pills in one part of pond decreasing effect of poison on other parts. Residual effect after Phostoxin treatment lasts for one week, which may be decreased to 4–5 days by liming. Fish killed by this material are edible.
Thiodin is the third fish poison used in Bangladesh. Its effective concentration is 0.10–0.15 mg/liter. Thiodin is highly dangerous for human beings. Fish killed with Thiodin are not fit for consumption. Waiting time after Thiodin treatment is at least one month.
Considering the fact that the residual or lethal effect of different fish poisons is determined by several factors, a small group of fish stocked in a hapa should be exposed for 24 hours to see the effect of pond water before stocking.
Farmers use poisons at the beginning of season, no fish poisons are used between consecutive cycles of nursing. It is one reason why survival (and growth) is better usually in first cycle of nursing than later.
Lime is used for killing different living organisms remaining in muddy pools after dewatering of ponds. Moreover, with sharp changing of soil pH bacteria prevailing in upper layer of mud are controlled by lime scattered on whole bottom surface and the new chemical environment facilitates blooming of more productive aerobic bacteria population. Some minerals become more accessible for living organisms after application of lime.
Usually two different types of lime are available in Bangladesh for pond treatment:
Efficiency of the two materials differ. In effectiveness 100 kg of hydrated lime is equal to 70 kg quicklime. Considering the fact that soils in Bangladesh have usually significant quantity of colloid fractions, depending on soil pH 40–100 kg quicklime or 60–140 kg hydrated lime are suggested for liming 1 bigha nursery pond. While applying lime, it should be taken into consideration that the efficiency of lime depends on particle size. So powdered quicklime or well diluted hydrated limes are most effective.
If ponds are not dried before preparation for new stocking, frequent application of small lime doses is suggested. 10–20 kg hydrated lime scattered on one bigha pond surface daily has a favorable effect on pond ecosystem. When combined with organic manuring, it eliminates turbidity of pond water.
Nursery ponds are to be partially refilled 4–7 days before the time of planned stocking. Desirable depth of pond is not more than 3.0–4.5 feet. As time of stocking is imminent, large dose of manure should be avoided. 100–150 kg poultry manure or 200–250 kg cattle dung should be scattered uniformly per one bigha pond on commencing day of pond preparation. Manure should be distributed simultaneously with refilling of pond. No additional manuring is suggested on the day after preparatory dose of manure, but from following day 10–15 kg poultry manure or 20–25 kg cattle manure should be spread daily on one bigha pond surface for a period of 3–6 day. If refilling of pond is carried out with well water, it is better to add in addition to organic manure 3–5 kg urea/bigha and 2–3 kg triple superphosphate/bigha for promotion of algal development. If pond water loses its green color after organic manuring, it is advisable to mix daily dose of organic manure with 400–450 g urea and 50–100 g triple superphosphate for promotion of algal blooming for a few days. In absence of organic manure, a mixture of soaked mustard oil cake and artificial fertilizers may be used for pond preparation and plankton maintenance. Suggested doses for preparation of one bigha pond are: 20–40 kg mustard oil cake, 3 kg urea and 1 kg TSP, soaked for 24 hours.
Preparation of an undrainable pond should commence about one week before stocking. Frequent application of small doses of manure is suggested. Doses are similar to manure doses mentioned before for drainable ponds.
If ponds are filled with well water and are manured as suggested above, usually mass blooming of pure ratifera population will occur. In undrainable ponds or in ponds filled with pond water, plankton organisms that prevail from before (usually mixed population of cladoceras and copepods) start blooming after application of preparatory doses of manure. If pond water is treated with Dipteryx at the rate of 0.5–1.0 mg/l, or with Sumithion/Edithion at the rate of 1.0–3.0 mg/l copepods (Cyclops) and cladoceras are killed and the most favorable organisms, ratiferas, start to develop. The best time for chemical selection of plankton organisms is 3 days before fish stocking. (It is worthwhile to mention that after repeated Dipteryx treatments of a pond, organophosphate resistance of Cyclops population can develop, and it is not possible to eliminate such resistant populations. Pond containing resistant organisms are not suitable for stocking of newly hatched fry.)
In pond waters, made rich with organic materials by organic manuring, dense population of water insects can develop within 1–3 days after refilling. Chemical treatment (Sumithion/Edithion or Dipteryx) of water can control this blooming of insects only for 1–3 days period. The most common organisms in developing aquatic insect population are the backswimmers (Figure 10). Majority of backswimmers are harmful for newly hatched fry. So frequent control of insects is essential. Sumithion/Edithion treatment, applied at the rate of 0.25 mg/liter 10–15 hours before stocking can temporarily eliminate backswimmer population. Considering 5 feet water depth, 400–500 ml of Sumithion/Edithion is necessary for treatment of an one bigha pond. Dipteryx, Sumithion/Edithion and Thiodin (mentioned earlier in section 2.4.1) are strong poisons and can enter into human body through the skin or by breathing. For handling and sprinkling of these materials wearing of rubber gloves is suggested. If such gloves are not available, a polyethylene bag can be put on hand before treatment of pond with these chemicals. Wind direction should be considered at sprinkling. It should be done by moving backwards toward wind direction.
Sequence and short description of activities necessary for pond preparation are summarized in Table 13. Synchronization of hatchery activities and works of nursery pond preparation is summarized in Table 14.
PRE-STOCKING POND MANAGEMENT
|Dewatering||10–12 days before stocking. The most effective method of eradication of unwanted fish and aeration of pond soil.|
|Poisoning||10–12 days (or one month) before stocking. It is necessary in undrainable ponds. 2–3 mg/l. Rotenone, 0.25 mg/l Phostoxin, or 0.15 mg/l Thiodin (waiting time one month) are suitable.|
|Liming||5–6 days before stocking. 40–140 kg lime/bigha after dewatering, or 40 kg/bigha followed by daily 10–15 kg for 1 week.|
|Bottom treatment||Racking the bottom of undrainable ponds for a few days for aeration of upper soil layer.|
|Partial or total refilling||3–4 days before the planned stocking. The required water depth is at least 1 m.|
|Manuring||3–4 days before the stocking (on the day of refilling) 100–150 kg poultry or 200–250 kg cattle manure for one bigha as a preparatory dose followed by 10–15 kg or 20–25 kg daily dose.|
|Fertilization||If well water is used for refilling (or algal blooming is not sufficient in undrainable ponds) in addition to manure 5–7 kg/bigha Urea and 3–4 kg/bigha TSP followed by daily dose of 0.5 kg Urea and 0.2 kg TSP.|
|Eradication of Copepods||30–50 hours before stocking Dipteryx treatment (0.5–1.0 mg/l) or Sumithion/Edithion (2.0–3. Omg/l) if Cyclops are present in the water.|
|Eradication of water insects||10–15 hours before stocking 0.2–0.3 mg/l Sumithion/Edithion treatment|
|Stocking||1.5–7.0 lakh fry for 1 bigha pond.|
SYNCHRONIZING OF HATCHERY WORK AND POND PREPARATION OF UNDRAINABLE PONDS
|Schedule of activities||In hatchery||For pond preparation|
|12 days before stocking||-||Poisoning, repeated netting|
|6 days " "||-||Liming|
|5 days " "||Injection/stripping||Refilling, manuring|
|3 days " "||Hatching||Raking of pond bottom|
|2 days " "||Cleaning of larvae keeping tanks||Dipteryx treatment|
|1 day " "|
12–20 hours before stocking
|Cleaning of larvae keeping tanks||Raking of pond bottom|
Sumithion/Edithion treatment, repeated netting
|0 day||First feeding of fry 3–4 hours before stocking||Stocking|
The best time for stocking of fry are morning hours in cloudy days and afternoon period in sunny days. They should be released after acclimatization (continuous equalization of water temperature and quality). Keeping plastic bags containing fry on surface of ponds for equalization of water temperature is not recommended, because water temperature in bags will increase soon due to strong sunshine. Acclimatization should be done in shade.
Stocking density depends on production target. If the target is production of small size dhani (with average weight of 0.1–0.2 g), stocking density is 2–5 million feeding larvae/ha and length of nursing is 12–15 days. If production target is 1.0–1.5 inch (2.5–4.5 cm) nursed fry with average weight of 0.2–0.6 g stocking should not exceed 1.5–1.8 million/ha and duration of rearing period is 2–3 week.
The important task of fish culturists after stocking is the maintenance of plankton population. Most efficient way of plankton maintenance is frequent manuring with small doses of poultry or cattle manure. In addition to plankton maintenance, frequent manuring maintains an active and effective bacterial population in pond water. It facilitates decomposition of metabolites hampering fish growth. 5–15 kg poultry or 10–20 kg cattle manure is sufficient for daily treatment of an one bigha pond. If animal manure is not available, soaked mustard oil cake also is good for pond maintenance. If algae blooming is not sufficient, some chemical fertilizers should be applied for daily treatment. Manure, soaked mustard oil cake and chemical fertilizers should be scattered equally on pond surface. As a consequence of organic material treatment, backswimmers can bloom soon in treated ponds. Sumithion/Edithion treatment should be repeated 2 times during first ten days of nursing if it is necessary. If Sumithion/Edithion is not available, Diesel oil treatment at the rate of 4 liter/bigha is also suitable for elimination of backswimmers.
Feeding of fish is not important during first 3–4 days period of nursing. Later on feeding is necessary in ponds where stocking density is higher than 1 lakh/ bigha. Soft dough-type feed comprising 2–3 kg soaked mustard oil cake, 2–5 kg wheat bran and 1–2 kg cattle blood or fish meal/bigha should be scattered daily on the surface. Important works of post stocking pond management are summarized in Table 15.
POST STOCKING POND MANAGEMENT
|Increasing water level in pond||5–6 cm rise in water level daily for 5–10 days for maintenance of good water quality.|
|Treatment of bottom||Daily harrowing the pond bottom during rearing period.|
|Maintenance of plankton||5–15kg poultry or 10–20 kg cattle manure for one bigha pond daily. If the algal production (the water color) is not satisfactory, in addition to manure 0.5kg urea and 0.2kg TSP is suggested.|
|Insect control||Two Sumithion/Edithion treatment (0.25 mg/l) on every third day in ponds where newly hatched fry are stocked.|
|Feeding||No feeding is necessary in first 3–4 days. Later mixture of mustard oil cake, wheat bran and cattle blood must be fed, at the rate of 5–10 kg/day/bigha, in pond stocked more than 1 lak fry/bigha.|
When the fry attain desirable size (1–2 weeks after stocking) they should be harvested as soon as possible. Quantity of natural food organisms (Cladocera and Copepoda) is very low at this time. Keeping fry in ponds without natural food will cause outbreak of diseases.
Rubbing of small size prenursed or nursed fry to net should be avoided at harvesting. By splashing water from behind the net fry can be expelled from net easily.
Dense population of fry gather at water running into pond in early morning period, before sunrise, when oxygen is in lower concentration. Low lift pump is suitable to create water current for luring and concentrating fry to a small area of pond.
Fingerlings are produced in the country using different methodologies. Only one cycle production is achieved by majority of farmers in one season. They grow up fingerling in single or in dual stage. If fingerlings are produced in single stage, stocking density of fish is about 0.8–0.9 million newly hatched fry/ha. Fingerlings of 2 inch size are harvested after 60–80 days of rearing. Survival is usually low in this rearing system. Other way of fingerling production is the dual stage system. About 2 millions of feeding fry/ha are stocked and “dhani” ( 15 mm long prenursed fry) is harvested within 10–12 days. After harvesting, dhani are stocked in fingerling rearing pond, at the stocking density of 0.4 million/ha. Fingerlings are harvested after 3 month. Majority of them are 1.5–2.0 inch, but 10–15 percent of fish are harvested later at the size of 2.5–3.0 inch.
Other methodology of fingerling production is applied in Jessore area. Farmers practice here multicycle method of fingerling production. Prenursed fry are produced in first step and fingerling production ponds are stocked with this prenursed fish. Stocking density at fingerling production is about 1.4 million dhani/ha/cycle. Duration of rearing period is about 30 days. Fingerling production is repeated 4–6 times/season. (Mentioned methodologies are summarized in Table 16).
Majority of fingerlings produced in Bangladesh are 1.5–2.0 inch. This size of fish are easy to transport as well as are suitable for stocking of well prepared market size fish rearing ponds. However, this fingerlings are too small for stocking in open waters. Birds, frogs, carnivorous fish and water insects can prey on them.
Implementation of the Asian Development Bank and Word Bank sponsored Second and Third Fisheries Projects for utilization of temporarily inundated areas for rearing market size fish has created new demand for carp fingerlings. As those projects stipulate 400–500 million 4–5 inch size fingerling to be released in open waters every year. To achieve this target, private sector should significantly increase its production for supply to these projects. Moreover, the present technology of fingerling rearing should be changed. Instead of 1–2 inch size fish 4–5 inch size fingerling should be reared for stocking in natural waters.
TECHNOLOGY OF FINGERLING PRODUCTION APPLIED BY LEADING FARMERS OF PRIVATE SECTOR
|Nursing||About 5 million feeding fry are stocked per 1 ha for prenursing.|
|Fingerling production||Duration is 25–35 days|
|Poisoning of ponds||Poisons (mainly Thiodin at the rate of 160–225 ml/bigha) is used only at beginning of the season.|
|Liming||2–3 days after poisoning 30–40 kg/bigha CaO is applied. (Only 50% of farmers use lime.)|
|Fertilization (in-organic)||Few days after liming 30–70 kg urea, 50–80 kg T.S.P. and 15–30 kg muriate of potash is used for 1 bigha pond.|
|Manure (organic)||50–80 kg soaked mustard oil cake is used for 1 bigha pond after. It is sprinkled on whole pond surface after 4–7 days soaking.|
|Stocking||After testing the effect of poison, 7–14 lak of dhani (av. length is 1/2 inch) are released.|
|Feeding||Feeding is carried out once a week, applying 20–40 kg/bigha mustard oil cake.|
|Sampling||Fry are netted once a week and released again in pond.|
|Bottom treatment||Bottom racking by pulling horra.|
|Harvesting||It starts after 2–3 week rearing, depending on market demand.|
|Repeated fertilization||Depending on colour of water mixture of urea and T.S.P. is used frequently, at the rate of 50–60 kg/bigha.|
There is no significant difference between pond preparation of nursery ponds (summarized in Section 2.4.1 – 2.4.3) and fingerling production pond, except that the organophosphate treatment of ponds is not essential. As prenursed and nursed fry used for stocking of fingerling rearing pond, can consume any size of zooplankton organisms, no Dipteryx or Sumithion/Edithion treatment is necessary for elimination of Copepods and Cladoceras. Sometimes, if population density of backswimmers is high and dhani are planned to stock, it is recommended to use 0.25 mg/l Sumithion/Edithion to eliminate their population temporarily.
As final weight of fish depends on stocking density, for production of large size fingerling, less number and for production of smaller size fingerling, more fish should be stocked. Relationship between stocking density and final weight of fingerlings is shown in Figure 11.
Relationship between stocking density and final weight of fingerlings
Large size fingerling production is usually carried out in polyculture. It renders more effective utilization of natural food organisms than monoculture. If large size fingerlings are to be produced in a 30–45 day rearing cycle, to achieve the required 10 g individual weight not more than 14 000 prenursed fry/ 1000 m2 should be stocked. It may be a combination of different species, but the stocking densities should not exceed the range of more than 5000 grass carp, 7000 silver carp, 3000 mirror/common carp 5000 catla and 3000 mrigal. But if improved feed containing cattle blood is applied, the stocking may be increased, even if the production target is large size fingerling.
For production of 5 g final size fingerling, approximately 20–25 nursed fry/m2, for production 3 g average size fingerling, stocking of 30–35 nursed fry/m2 is suggested.
To produce 120–130 kg/1000 m2 fingerling about 150 kg/1000 m2 feed (mixture of mustard oil cake and wheat bran) is necessary (Table 17, Feeding schedule I.) If production target is higher (200–230 kg/1000 m2) feeding animal origin materials (preferably cattle blood) is important, as it is shown in Table 17, in Feeding schedule II. For those ponds where grass carp is reared about 100 kg/1000 m2 duckweed are necessary.
FEEDING SCHEDULE FOR CARP FINGERLING PRODUCTION
I. Feeding schedule for 120–130 kg/1000 m2 production
|Culture period (days)||Ration||Mustard Oil Cake||Wheat Bran||Duckweed|
II. Feeding schedule for 200–230 kg/1000m2 production
|Culture period (days)||Ration||Mustard Oil Cake||Wheat Bran||Cattle Blood||Duckweed|
Manuring and bottom treatment
Daily 5–10 kg/1000 m2 chicken manure or fresh rumen content is suggested to spread on the whole surface of pond. Cowdung applied at the rate of 10–15 kg/1000m2/day is also suitable for maintenance of plankton. If algal blooming is not satisfactory, in addition to organic manure, daily application of small quantity of artificial fertilizers recommended at the rate of 0.3–0.7 kg/1000 m2. Daily raking of pond bottom is recommended.
In spite of intensive manuring fingerlings usually consume zooplankton organisms from rearing ponds within 30–35 days. After this harvesting of fish is recommended, because growth rate of fingerling sharply decreases, moreover fish diseases may outbreak in ponds if no natural food is available.