Pradyut Biswas
In India, fish culture has witnessed a rapid expansion in the last 2-3 decades. As the farmers became familiar with the technology of fish culture, they have modified the technology to suit their needs. Among the different modifications adopted by the farmers to suit their needs, use of stunted carp fingerlings round the year is important. The stunted fingerling when stocked in grow-out ponds at normal stocking density with optimal feeding and fertilization exhibited compensatory growth in terms of weight gain and survival in shorter culture period. Application of compensatory growth phenomenon by using stunted carp fingerling has been proved to have greater potential in increasing fish production.
In fish culture, the climatic condition of a particular place directly affects the fish production. A thumb rule of fish culture says that the higher the temperature higher the growth and lower the temperature lesser the growth. As per this thumb rule, the fish production remains low in the cold or colder region as in such area the growing period is less or lesser when compared to the warmer areas whereas the fish production increases in warm areas as in warm area the natural food of fish is easily produced. This fact is very much applicable in North Eastern region of India, as it remains cold or colder, where the growing period for fish ranges for 8-9 months in a year. Therefore, in this area either it is needed to stock stunted fingerlings (sometimes called as yearlings) instead of fingerlings in the pond around the end of March or April when the temperature of water starts rising so that farmers raise them to marketable size in one growing season of 8-9 months.
It should however be clearly understood that managing stunted fingerling ponds throughout the year is not an easy task and needs a lot of attention. Farmers risk fish losses and problems with predation, theft and water availability and quality.
What is stunted fingerling?
Stunted growth fingerling is when the fish physically appears to stop growing-either because of poor diet, poor water quality or by being in a tank that’s too small for it but have not yet attained full growth potential.
Why should you go for stunted fingerling?
· Carps are known to grow rapidly during the second year of their age.
· Higher survival rate in grow out ponds.
· More Immune to the diseases.
· More tolerant to environmental fluctuations.
· Require less time to reach marketable size (5-6 months).
· High growth rate and can be sold at higher prize.
· Higher production and productivity.
· Unhealthy seeds are perished during stunting periods, so we get only healthy seeds.
· Majority of seasonal water bodies dries within 5-6 months where fish rearing from advanced fries is not economical.
Pond management
Pre stocking
Stunted fingerlings can be reared in ponds from 0.1-0.4 ha in size ranging in depth from 1.5-2.0 m. These ponds should retain enough water in the summer so that the fingerlings are not affected. The ponds need to be made free from weeds, weed fish, predators. Weeds take nutrients out of the water. They hinder the movement of the fish. They also reduce oxygen during the night and early in the morning. These weed have to be taken out manually by hand. If there are not weeds in the pond, for destroying predators and competitors first apply urea at 100 kg/ha where the water is 1 m deep. After 24 hours apply 200 kg of fresh bleaching powder/ha. Fish start dying within one hour of adding the bleaching powder. These fish can be harvested and eaten. It takes a week for the toxic effect of bleaching powder to go. After that application of lime @ 300-500 kg/ha either before rainwater filling or after for pH corrections and disinfection can be done. Then the pond preparation involves application of cow dung (@ 2.5-3 MT/ha) and mustard oil cake @250-400 kg/ha as organic manure, sporadic application of inorganic fertilizers viz., NPK mixtures @ 60-75 kg/ha., urea @ 100-125 kg/ha. to pond water to facilitate better natural fish food production.
Stocking
The fish seed (fry) of mixed varieties of Indian major carps are commonly stocked after about 4-6 days of initial manure at densities of 4-5 lakh/ha. In sporadic instance grass carp, silver carp, common carp and others varieties like big head, calbasu, Puntius japonicus, etc. are also reared. The ratio of different species in seed stocking varies in accordance to supply, availability and demand in the region. The stocking density used is also based on the final growth desired for stocking in grow-out ponds. For example, at lower stocking density, fish would attain a weight of 100-150 g, but at higher stocking density, fish would reach about 25-50 g. Seed stocking is generally done in the cool evening hours.
In case of IMCs it is often recommended that these fish are stocked in the ratio 3:4:3. The best mix of the fry of Catla, Rohu and Mrigal depends on the pond. If there is a lot of debris on the bottom of a pond, more Mrigal (which is a bottom feeder) could be stocked or Common Carp added to the mix. If there are lots of submerged plants with tiny plants growing on them, which Rohu eats then more rohu could be added. Where lots of succulent grasses ae submerged, Grass Carp could be added to the mix. The stocking density is high for advanced fingerling production in perennial ponds because the target is slow growth and a fingerling that is small for its age.
Post-stocking
The stocked fry are fed daily with minimal amount of feed, i.e. good enough for their survival. Feeding with mustard cake powder and rice bran is a common practice. Initial feeding is done by direct broad cast method twice a day, once during morning and evening; later adding the feed in dough form in the same place helps fish to fed efficiently. Feed level should be reduced if the weather is cool and increased in warmer weather. Liming the pond at 50 kg/ha during October-November and again during March-April is a must. Periodic fertilization with fresh cow dung (1000 kg/ha) or a mixture of cow dung (500 kg/ha) and poultry manure (250 kg/ha) should be done every month. Feeding and application of the manure should be avoided on cloudy days when special attention must be paid to oxygen levels fall below the minimum requirement when the fish start coming up to the surface to gulp the air. Fry/fingerlings are reared in ponds for about 10-12 months when they usually attain 50-100 g in weight. During this period of stunting, weak and unhealthy seed are also eliminated from the system. Healthy seed which survive the stunting process are used for culture purpose.
Conclusion
Such stunted seed when stocked in the culture pond would compensate for the growth lost during the stunting period and attain a weight of one kg. Most importantly, the survival of such stunted fish is almost 100 per cent, except for mortalities dur to other environmental conditions. These advanced fingerlings can be stocked in perennial ponds, which have a resident population of competitors and predators (that cannot be removed), or in seasonal ponds which hold water for only 6-8 months.
This technology of stunting fish seed developed by farmers is considered as one of the most important practical solutions found by farmers to address the problems related to fish growth and yield. In commercial carp culture systems in many parts of India, this practice has completely replaced the conventional system of stocking fingerlings, and there is considerable improvement in health, survival and production. The use of stunted fingerlings will enable the commercial fish producers to have access to fingerlings all year round and therefore be able to stagger their harvest through the year. This would enable the producers to harvest more than one crop of fish a year. Stunted fingerlings will also enable farmers in temperate areas and areas with scanty water supply to produce table sized fish in a short duration of time. As stated earlier, farmers are now able to obtain, most commonly an average yield of 8 tonnes/ha and some of the progressive farmers obtain a yield of more than 13 tonnes/ha/year.
College of fisheries, CAU, Lembucherra
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