Dr V.R.P. Sinha
Freshwater Aquaculture Research and Training
Centre (CIFRI), Dhauli, P.O. Kausalyagang
Via Bhubaneswar-751 002
All food production is essentially a process of energy transformations. Solar energy is fixed by chlorophyll bearing plants, the primary production, and these in turn are consumed by small animals the secondary production, which is finally consumed by fish, the tertiary production. This straight food chain appears too simple but in fact it is really a complex of food network with various cross linkages.
Primary productivity is dependent on light, carbon dioxide, essentially salts and temperature, any one of which can be limiting. Of these factors affecting primary production in ponds the easiest to control is the quantity of dissolved salts. Both the nature and the quantity of fertilizer added are important, affecting both the species composition and the rate of primary production. For example, there is now growing evidence that as the phosphate content of the water increases, not only does the density of the photoplankton increases, but it also changes in a species composition. At lower concentrations diatoms are common, but as the concentration of phosphate increase green algae become more frequent, eventually giving way to blue-green algae at the highest concentrations. In addition to changing the species composition of the phytoplankton, excessive phosphate, through the production of surface blooms may lower the primary productivity through ‘auto-shading’. Thus both the nature and the quantity of fertilizer added are important, affecting both the species composition and the rate of primary production. In fish culture also as in terrestrial agriculture it is usual to add N.K.P. mixture as fertilizers, with sometimes trace elements included in the mixture. Terrestrial plants usually have fairly extensive root system, sometimes penetrating quite deeply into the ground. The soil structure is usually aerated, so that the roots can respire, while the nutrient salts are held in thin films of water in the soil spaces and are often quite firmly bound by electronic charges to the soil particles. For the root to obtain enough nutrients the salts may have to move some distance, against the electronic charges of the soil. The mobility of the salts will therefore be far less than those in the larger body of water. For this reason we have to add fairly large quantities of fertilizer to the soil for the growth of terrestrial crops, although only some of this fertilizer is taken up by the plants. The rest may be eventually leached out into rivers and lakes to add to the problem of eutrophication. In a pond only one to two inches of mud is concerned with salt exchange, and below this the soil is unaerated with negligible salt movement. As a result of this truly aquatic plants have shallow or negligible root systems. Absorption of salts is through all parts of the plant in contact with the water, while with algae, which have no root systems, absorption is entirely through the cell walls. Diffusion of salts throughout the water mass is quite rapid, certainly far faster than the movement through the soil, and therefore less fertilizer need be added to a pond. However, fertilization of pond will be dealt with separately and in greater details but it is stressed that fertilizer should be applied most rationally in a fish pond.
Under crowded conditions fish compete for the food supply, and they also suffer stress due to aggressive interaction. Under stress fish are found to eat less and grow more slowly, while in static ponds there is reason to believe that the excretory products of the fish may themselves tend to suppress their growth. If we look at actual total production as compared with the number of fish stocked we get a curve as in figure 1.
The effect of increasing the stocking rate on the total fish crp (In State ponds)
Number of fish per hectare
It will be seen that as the number of fish is increased production of fish increases to a maximum and then decreases again. Thus there is an optimum stocking rate which gives the highest production and the largest fish (this argument only applies to non-breeding fish). In running water where the excretory products are washed away, the production rises to a maximum and remains at that level however much we increase the number of fish. Thus in increasing the number of fish beyond the optimum point, all we are doing is increasing oxygen consumption by the fish, with its obvious dangers, without increasing the crop of fish. The fact that the light catalyses two photosynthetic reactions, the reduction of carbon dioxide to carbohydrate and the oxidation of water to give oxygen is of great importance because it is intimately bound up with the oxygen balance in the water and is much more delicately poised in static ponds. A mistake can cause mass death of fish with disastrous suddenness. There are three very important factors to be remembered in relation to oxygen balance:
The saturation value for dissolved oxygen in pure water at atmospheric pressure are as follows:
It should be quite clear from this that water saturated with air, without any addition of oxygen through photosynthesis, has more oxygen available for fish life at 20°C than at 30°C.
When plants are present the situation becomes much more complex. Not only do we have an additional source of oxygen, but the total biological respiration is also increased. On the other hand in dense growths of plants (algal blooms, dense weed beds) self-shading occurs so that those plants beneath are less able to photosynthesize. This is shown for phytoplankton in figure 2, which the in dotted line shows the expected oxygen production and the thick line shows the actual oxygen production.
This means that as the plants bècome denser more and more of the oxygen produced is used up in the respiration of the plants themselves and less is available for the fish. If we graph the amount of oxygen remaining, i.e., the daily increment of oxygen added to the water, against total oxygen production, we obtain a characteristic curve (figure 3).
Fig. 2 Effect of autoshading of the phytoplankton on oxygen production.
Fig. 3 Graph of daily increment of oxygen against daily gross production.
It will be seen that an oxygen production increases the amount available after the respiration of the plants themselves, i.e., the amount available for the fish, increases to a maximum and then decreases to zero, and at a very high gross oxygen production (i.e., very dense algal blooms) the plants actually use up more oxygen than they produce. However, figure 3 only deals with conditions when there are several sunny days but if there are cloudy days the situation becomes much worse. We can see this better if we examine the diurnal fluctuations of oxygen; oxygen rises to a maximum during the day and falls to a minimum at night. Figure 4 shows these fluctuations.
Fig. 4: Diurnal fluctuation of oxygen
Curve I represents an ideal condition in sunner periods, where there is a daily addition of oxygen, produced by photosynthesis. Curve 2 represents the critical conditions in sunny period with heavy weed infestation or algal bloom when most of the oxygen produced by photosynthesis is used up in weed and plankton respiration. But, difficulties arise when there is a cloudy day, the total amount of oxygen produced is less. Yet, there is still enough oxygen (Curve III) in those ponds which have no heavy infestation of algal bloom or weed to maintain a fish population. But those ponds which are heavily infested with algal bloom or weed shows the oxygen fluctuating below the critical level (Curve IV) for fish survival and mass mortality occurs. Therefore, it is important that the pond water should provide adequate oxygen to support the total biological respiration during the hours of darkness and also adequate oxygen during the less favourable warm, overcast or rainy days.
In mixed culture the fish usually stocked are a mixture of plankton feeders and macrophyte (waterweed) feeders. The nutrients added to the water are taken up by both phytoplankton and the macrophytic water weeds, but as with land plants, they may not grow at the same pace, so that one group may use up most of the nutrients leaving little for the other. In ponds we try to maintain a balance by using both the phytoplankton to feeders and the water-weed eaters. If we use only fish that eat water-weeds, these may be heavily grazed and the nutrients released may then be taken up by the phytoplankton, which becomes denser and denser, shading out the submerged water-weeds and preventing them from growing again. If we only use the plankton feeders, the phytoplankton may become so heavily grazed, that the ungrazed submerged water-weeds grow very fast and use up all the nutrients. The plankton feeders will then starve. Sometimes not all the phytoplankton is grazed and we then have zooplankton developing (minute crustacea, rotifers, etc.). These also can be grazed down. We try therefore to achieve a balance where both phytoplankton and water-weeds can grow, and to have different species of fish grazing down both.
Chinese system of culture involves Chinese carps such as black carp, Mylopharyngodon piceus living on snails or other molluscs at the pond bottom; (ii) grass carp, Ctenopharyngodon idella, the macrovegetation feeder; (iii) silver carp, Hypophthalmichthys molitrix, a phytoplankton feeder; (iv) big head, Aristichthys nobilis, eating macroplankton; (v) common carp, Cyprinus carpio, an omnivore; (vi) Prabramis pekinensis, also an omnivore; and (vii) mud carp, Cirrhinus molitorella, a bottom feeder. The selection of suitable species for stocking depends on the nature of soil and water of the ponds, the availability of stocking material, consumers' preference and the kinds of fish food organisms available.
Indian system involves the Indian carps. Indian carps such as Catla catla, Labeo rohita, Cirrhinus mrigala, and Labeo calbasu are cultured in the northern belt whereas Labeo fimbriatus, L. kontius, Cirrhinus cirrhosa, etc. in the southern belt of the country. Their farming is widespread and thus the systems differ according to the availability of the species, local preferences etc.
The Chinese and Indian carps do not normally breed in confined waters such as ponds and tanks and as such before the development of induced breeding technique, the rivers were the main source of fish seed which constituted mixed variety of several desirable and undesirable species. Seed collected from rivers was stocked in ponds and in this way a system of mixed culture or polyculture developed.
Traditionally there was not much of control on the density or ratio of different carps while stocking. However, with extensive experience the fish farmers arrived at some ratio. Under this system, average productions ranged between 100 to 1000 kg/ha/year. However, after extensive experimentations the production rate has been increased about five to six times. A production as high as 5,200 kg/ha/12½ months has been obtained by stocking Indian major carps @ 7,500/ha in the ratio of 3.5:3.5 and 3.0 catla, rohu and mrigal respectively during 1974–75. The technology of polyculture or mixed culture of Indian major carps includes the removal of predatory fishes from the pond by using suitable ichthyocide, fertilizing the pond with both organic and inorganic fertilizers and feeding the stocking fishes with supplementary feed.
Further the introduction of exotic Chinese carps e.g. grass carp, silver carp and Bangkok strain of common carp into India in the late fifties added these species to the family of cultured carps. These exotic species are non-predatory, fast growing and compatible with Indigenous ones.
A series of experiments have been conducted at the CIFRI, Cuttack, on the culture of these three exotic carps; silver carp, grass carp and common carp to know their suitability under Indian conditions. Productions varying from about 2,896 kg/ha/yr to 3,287 kg/ha/yr were obtained. The best result was obtained with silver carp, grass carp and common carp stocked in the ratio of 3:1:2 at the stocking density of 5,000/ha. Aquatic weeds were given to grass carp in addition to supplementary feeds such as mustard oilcake/groundnut oilcake and rice bran. Ponds were fertilized with both organic and inorganic fertilizers. Also it was found out that these three carps always gave better rate of production when they were stocked with Indian major carps than when Indian or Chinese carps were stocked alone under identical managerial/material inputs. Thus a high yielding combination of six-carp species commonly known as composite fish culture was evolved. Composite fish culture is also a polyculture but is little different than Indian or Chinese system of carp culture since under this system both Indian and Chinese carps are stocked together.
As far as possible, pond should be stocked with silver carp, the percentage of which may be 10 to 20 depending on the availability of the seed. Catla is also stocked and it is suggested that the combined stocking density of silver carp and catla should not exceed more than 30 to 35%. Both silver carp and catla feed mainly on surface and thus they are grouped as surface feeders. Growth is normally affected if their proportion in the stock is more than 30–35%. Rohu feeds in the underwater is called a column feeder and does grow well in deeper ponds. Therefore, ponds having more than 3–4 meter depth of water need to be stocked with 15 to 20% of rohu. In shallow ponds the stocking density of rohu should not be increased more than 10% of the total stocking density. Bottom feeders such as mrigal and common carp are stocked at a higher ratio which may together account to about 40–45%. Availability of aquativ weeds in the pond or in the vicinity decides the stocking density of grass carp. It is always desirable to keep 5 to 10% grass carp, and manage to feed it with aquatic weeds, green vegetables or even with land grasses.
It has been seen in different parts of India that despite higher numbers of Chinese carps used for stocking in Composite fish culture, they have recorded better growth rate than Indian major carps. However, their wide spread use is dependent on the availability of their seed.
Catla and silver carp both are planktophage surface feeders, though catla is predominantly zooplanktophage and silver carp phytoplanktophage. Because of their similar feeding zone and feeding habit it is assumed that their exists some competition between these two species for the same ecological niche. Various combinations of catla and silver carp have been tried. Stocked in equal numbers at Kausalyagang, silver carp attained almost double the growth reached by catla at comparable survival rates. Silver carp at double the numbers of that of catla, the former invariably grew faster achieving weights double that of catla, at times even more than double. It is interesting to note that in one of the experiments at Pune centre, where the highest fish production rate of 10,670 kg/ha/year has been achieved, catla and silver carp attained an average weight of 1300 g and 2100 g respectively in one year when stocked in the ratio of 1:2.5, the total stocking density of all the 6 species being 10,000/ha. Even at the increased ratio of catla 1: silver carp 3, the latter species gave better result. Similarly, in the other centres also catla always grew less than silver carp. For example, at Kulia fish farm, catla in 6 months recorded a weight of 525 g with an average monthly increment of 70 g and in 12 months about 1208 g with an average monthly increment of 99 g compared to monthly increment of 80–131 g shown by silver carp. In 8 months catla grew at Karnal to 992 g, with monthly growth rate of 122.7 g, compared to monthly increment of 191 g shown by silver carp. During a period of 12 months at Pune, catla recorded the range of average growth of 810–1648 g with monthly increment rate of 66.9– 137.3 g compared to 114, 174 g range of increment shown by silver carp respectively in those experiments. At Jaunpur catla showed the range of monthly increment from 78–90 g whereas silver carp showed 159 to 264 g.
Stocked at equal numbers, growth performance of mrigal and common carp appears to be similar in cases where supplementary feed was not supplied adequately. However, when supplementary feeds were given in large quantities, common carp stocked in larger numbers performed much better than mrigal, indicating its superior capability of utilizing artificial feeds than mrigal.
Common carp attained an average weight of 600–1000g (average monthly increment being 99.8–82.1 g) at Kulia, compared to the monthly average increment of 83 g shown by mrigal. At Karnal, during 8 months, the common carp recorded a weight of 1187 g with 147 g as average monthly increment compared to 89 g of monthly increment by mrigal. At Jaunpur common carp showed monthly increment of 125– 128 g compared to 67 to 119 g in mrigal. During a period of 12 months common carp showed monthly average increment range from 96–117 g in different experiments at Pune Centre whereas mrigal showed the range from 76–107 g.
Association of grass carp in composite fish culture has an indirect benefit too. The excreta consisting of semi-digested vegetable matter, serve as the food of bottom dwellers e.g., mrigal and common carp. However, grass carp is also well known utilizer of supplementary feeds like rice polish and oilcakes. In order to avoid competition among grass carp, rehu, mrigal and common carp for taking supplementary feeds it is advisable always to provide aquatic weeds in adequate quantity to grass carp.
Thus the concept of polyculture involves judicious exploitation of all the niches available in the pond. However, while use of extraneous fertilizers and feed increases the productivity, it modifies the natural balance in the ecosystem, which also needs to be judicicusly exploited. For example, the nutrients added to the water are taken by both phytoplankton and aquatic macro-vegetation and if there is a mismatch in their growth rate and their exploitation, one group will dominature the other with adverse consequences. Normally, not all the phytoplankton is grazed and consequently zooplankton develop for which zooplankton feeder is included in the system. Many combinations are being tried in different countries according to the availability of seed and the local preferences. However, any similar combination could work just as well as it is the principle of ecological balance which is important. Thus, in composite fish culture not only judicious combination of species is required but also proper management techniques, such as preparation of ponds prior to stocking, stocking management, fertilization of the water and supplementary feeding to the fishes are necessary to achieve optimum production.
Our lands are characterised with period of ‘no rain’ and ‘plenty of rain’. With the onset of monsoon torrential downpours sweep across the land and the amount and frequency of rain decreases towards the end of the rainy season and thus when there is too much water from rainy monsoons severe floods occur whereas a late monsoon or one that ends far too early result in serious drought. Both flood/rain and drought influence the ecosystem of ponds on such lands. Small, shallow and seasonal ponds get filled or dried whereas deeper and perennial ponds exhibit considerable fluctuation of water level accordingly. However, compared to shallow seasonal ponds the bottom of the perennial ponds is never exposed to sunlight and therefore the whole ecosystem of such pond is quite different with those of shallow and seasonal ponds. Though these ponds are for multipurpose uses ranging from supplying drinking water for human population, to agricultural and livestock, recent trend is to utilize them for fish culture. Yet, the water depth is a crucial factor for proper management practice and in most cases also a limiting one. Normally, the only water source for these undrainable ponds is the heavy rainfall during the monsoon period. After the monsoon ceases the water level starts to decrease gradually and the water shortage is quite common as the end of dry season approaches and that is most crucial time for fish culture since the fish growth rate is faster then. In fact, the fish biomass is the maximum when water is the minimum, which poses serious problem to fish culture. Studies conducted on the filling up of the undrainable ponds through various sources of water supply indicated that the cost was minimum for the water drawn from irrigation canal followed by tube wells run by electricity, diesel and dug well.
|Sources of water supply||Cost of water supply per hectare-meter||Diesel rate per lit.||Electricity rate per KW/hr|
|Irrigation canal||IRs 1080.00|
|Tube well (electricity)||IRs 1200.00||IRs 0.16|
|Tube well (diesel)||IRs 1800.00||IRs 1.31|
|Dug well||IRs 2250.00|
One of the main features in these undrainable old rural ponds is the very thick sediment layer accumulated during the centuries. The newly constructed, reconstructed ponds and those which were freshly excavated removing the old thick sediment layers have more shallow sediment. The actual sediment layer in these ponds depends on several factors. The maternal soil has a decisive role, but the method of construction, the nature of embankment, the rapid resilting, the macrophyte cover, the relief of the bottom, the pond productivity, the fish stocking, all modify the sediment thickness of the ponds shortly after construction or sediment removal. The same factors determine the sediment thickness also in old ponds. There is a close correlation between the age of the fish ponds and the sediment thickness. The age-depth relationship shows a marked difference in ponds having different area. The smaller ponds increase their sediment layers more rapidly. After 20 years, they may have the same sediment depth than the larger ponds after 50 or even 100 years. An analysis of the nutrient status of these ponds shows, however, that the old pond sediment contains more organic matter and inorganic nutrient per unit weight or volume than the smaller ones having the same sediment thickness.
Actually, the thick sediment layer in the old undrainable ponds has a very significant organic and inorganic nutrient pool which need proper recycling.
Under such circumstances, the most recommended fish toxicant to eradicate the undesirable fish from the pond is mahua (Basia latifolia) oil cake which acts both as fish toxicant as well as organic manure which should be substituted by calcium hypochlorite Ca(OCl)Cl. The cost of mahua oil cake for application in one hectare-meter of water comes to about Rs 3250/- compared to Rs 1052/- for the same amount of water in case of bleaching powder. On the basis of a series of experiments conducted in the lab as well as in the field at FARTC it has been found that bleaching powder can be used as a substitute for mahua deoiled cake. Bleaching powder has been found effective @ 25–30 ppm for killing various unwanted fish species including Channa striatus, C. gachua, Glassogobius giuris, Heteropneustes fossilis, Mystus cavassius, M. bleekeri, Ompok bimaculatus, Wallago attu, Anabas testudineus, Etroplus suratensis, Nandus nandus, Puntius sarana, Oxygaster bacaila, Ambl ypharyngodon mola, Ambasis ranga, A. nama, Puntius ticto etc. It has got the additional advantage of disinfecting the pond and also retaining the toxicity for a shorter period. Plankton and benthic fauna start developing from 8th day of the treatment.
The sediment organic-C ranged between 3.2 and 47.7 mg g-1 dry sediment in certain ponds surveyed by the Centre. The highest amounts are found in the old pond with thick sediment layers. In newly constructed or sediment excavated ponds the organic content is very low. All the basic nutrients in the sediment water are many times higher than in the above layer water column. The large nutrient store is, however, locked in the sediment and remain unused. A study reveals in certain ponds that the daily release of ammonia is around 20 mg m-2 and that of phosphate is less than 2 mg m-2. The ammonia uptake potential is as high as 261 mg dm-3h-1. This means that several grams of ammonia is required instead of 20 mg to cover the nutrient requirement in the water column. The low population density of the common carp and other benthic communities are not sufficient to maintain a proper condition at sediment water surface. Blue green algal group (Microcystis) is able to utilize the sediment nutrient during the early development stage as well as during their diel vertical movement. The diel investigation of the O2 and temperature condition in most undrainable ponds characterised by anaerobic sediment and the limited O2 and nutrient transport. Therefore, it is highly essential to recycle the nutrient already locked in the soft sediment either by manually, mechanically or biologically - perhaps by stocking heavily common carp in such ponds. Studies are undertaken to see how best the nutrient already locked could be utilized by these means.
Outbreaks of communicable diseases are result of interactions between the three factors - the pathogen, a susceptible host the fish and the pre-disposing environmental condition prevailing in such ponds. Under high level of of intensification the risk increases. In order to achieve optimum production the fish must be kept as healthy as possible throughout the culture period which can be achieved through proper fish health management involving three sequential steps, viz., (i) prophylactic measures, (ii) fish health monitoring and (iii) treatment. Prophylactic measures include sanitation of ponds using disinfectant like bleaching powder or quicklime prior to stocking. Prophylactic therapeutic treatments against parasites and other microbial pathogens are done prior to stocking as well as during trial netting and subsequent handling.
Recently, it has been a seen that antibiotic treatment particularly with combiotic antibiotics (Penicillin + streptomycin) prevents the outbreak of Columnaris disease in certain carps. The disease normally occurs because of stress and consequent of rough handling. The doses vary from 25–30 mg of Streptomycin and 20,000–25,000 i.u. of penicillin/kg body weight when given parenterally. Similarly, diseases caused by other bacteria such as Aeromonas and Pseudomones sp can be controlled by Chlorampheniol when fed at the rate of 50–75 mg/kg body weight with feed for 5–10 days. Other common prophylactic treatments are a the dip treatment of fingerlings/fish with formalin, potassium permanganate.
Apart from adopting prophylactic measures it is essential to check the health status of cultured fish quite frequently. This helps in timely detection and diagnosis so that immediate treatment measures can be adopted depending upon the nature of the disease. Significant differences in growth rate among population of the same age may often be a sign of some chronic internal diseases. Diseased fish exhibit either or both physical and behavioural signs among which most common are listed below:
Common clinical symptoms shown by the fish are: (i) excess nucoms secretions, (ii) change in normal colouration, (iii) erosion of scales, fins, part of skin etc., (iv) erosion of gill lamellae, decolouration of gills, (v) formation of cysts, patches over the gills, body etc. and (vi) abdominal swelling and bulging of eyes etc. These necessitate immediate diagnosis of the disease and the proper treatment.
Fish attains table size normally within one year of rearing period. Final harvesting is done by seine net either during summer months when the water level depletes to the danger level or after the monsoon or when the market demand goes up. However, harvesting in larger and deeper ponds poses serious problems. While surface feeders are easily caught, bottom dwellers escape. It has been seen that the conventional drag net could collect about 90% of surface and column feeders whereas only 20–40 per cent of bottom dwelling fishes are caught with the same number of hauls in small ponds. To have maximum catch of bottom dwellers from large and deep ponds, a pocket net was designed which appears to be more effective and the operational efficiency in catching bottom dwelling fishes appears increased many fold.
The free bottom of the drag net is provided with a nylon twine, with sinkers and passed through the bottom series of the meshes. The free end of the net is then turned over to the main net and attached at equal intervals to a second line of nylon twine forming pockets. Each of these pockets are tied with 12 metal sinkers (6–8 g each). Large pockets with more sinkers may cause problem by going more deep inside the loss mud.
Small pieces of drag not approximately of sizes 15 × 5 m may be used and these pieces may be joined to form one net as per the requirement of the pond size. Thsi not is more effective if the pond bottom is not abnormally uneven.
In large and deep ponds, the part haul operation of this net is more effective than the complete netting. Scaring the fishes and encircling one corner by this net is proved effectives.
Bottom weeds and other obstacles like stones, roots of submerged plants etc. are to be cleaned before operating the net.
Other common problems which encountered in such ponds are listed below:
The initial decay of the dead aquatic organisms and sediment detritus by microbial activities and breakdown of organic compounds manifests in the form of various gases which enter the water column, and consume oxygen to the extent of axoxic condition and consequently cause the mass fish kill and planktonic collapse.
During summer months the high rate of decomposition of organic matter in the sediment results in vigrous bacterial biosynthesis and replication and sometimes this results in the excessive population and forms a temporary bloom of bacteria in the pond. Such blooms cause high oxygen demand, also leading to oxygen depletion and resulting mass fish kill. Recently such a bloom of sulpher bacteria has been observed in one of the ponds.
Temporary or permanent blooms of the blue green algae is of common occurrence which may be considered as a factor for mass mortality owing to the oxygen depletion. Pond having high human and cattle population in its surroundings have developed permanent bloom of Microcystis due to significant organic load.
Although a number of papers has been published with classical hydrobiological approach on different types of water bodies but not much is known about the basic production processes in rural undrainable ponds, which abounds in our countries. Therefore in order to quantify the main production process in these ponds, the Centre has developed a pond environmental monitoring system wherein 31 simple measurable parameters involving the basis and most important physico-chemical, microbiological and biological parameters have been selected to indicate on a comparative basis the architecture and the main production processes in the perennial undrainable ponds which have a very distinct ecosystem compared to lakes or reservoirs or even shallow seasonal ponds. Table I indicates these parameters, which are having direct relevance to the fish culture practice in these ponds. It has been avoiding other parameters which require sophisticated instrumentation and highly skilled staff. Very simple methodology is known for assessing pH, oxygen, alkalinity, NH4-N, NO3-N, PO4-P, organic carbon and total plankton including bacteria etc. and if the fishery extension workers are trained in such simple monitoring process they can easily know the status of pond productivity and accordingly manage the pond or train the fish farmers suitable for optimization of fish production in such perennial undrainable ponds.
A survey programme on 32 rural fish ponds scattered in Cuttack and Puri districts has been completed with the above monitoring system. Preliminary investigations show that the water column of these undrainable rural ponds although has a very high production potential under the given climatic condition, is presently infertile due to the overall nutrient deficiency with a very pronounced nitrogen limitation. At the same time there sediments have a very large amount of organic and inorganic nutrients almost locked and unutilized due to the anaerobic nature brought about by the very limited nutrients and oxygen transport within the water column and at the sediment water interface. The sediment contain practically no animals as natural food for benthophagous fish species. The only organisms which can flourish under these circumstances is the blue-green algal species of Microcystis. Further work is being continued to confirm these findings and also evolve suitable management methods to recycle the nutrient from the pond bottom mud to make the pond more productive.
Data evaluation sheet for perennial pond