World Aquaculture 29 Potential Steps to Increase Fish Production Improve pH of fish ponds The northeastern region has more acidic soils than other regions of India. Water pH is an important criterion to produce an adequate amount of natural food in the water through effective release of nutrients. Application of lime is essential to rectify pH of water. In rural areas, the availability of lime may be a constraint. In place of lime, ash produced at home from cooking fires or from various other sources can also be used (Figure 1). Ash produced from banana has a very good impact in improving pH of water. As a general rule, three kg of ash has the same effect as one kg of lime. Ash is also a good fertilizer and, hence, farmers are advised to apply all available ash to fish ponds. Stock stunted seed of higher weight Indian major carps, particularly rohu and mrigal, grow rapidly in the second year of life. Farmers in Andhra Pradesh stock stunted fish that are 6-8 months old and allow them to grow in the second year to their full potential (Figure 2). The average weight of rohu stocked in Andhra Pradesh is about 100 g. Such fish will grow to about 1 kg Table 6. Fish supply and requirements in Northeastern States States Total population Nutritional requirement Production Deficiency (T)@ 11 kg per capita (T) (T) Arunachal Pradesh 1097968 12077.65 2652 9425.65 Assam 26655528 293210.81 180950 112260.80 Manipur 2388634 26274.97 17600 8674.97 Meghalaya 2318822 25507.04 5147 20360.04 Mizoram 888573 9774.30 3680 6094.30 Nagaland 1990036 21890.40 5560 16330.40 Tripura 3199493 35191.23 17980 17211.23 Sikkim 540493 5945.42 140 5805.42 Northeast 39079257 429871.83 233709 196162.83 Table 7. Area utilized for aquaculture and potential area suitable for aquaculture State Area under Area available for aquaculture (ha) aquaculture (ha) Assam 60000 31232 Arunachal Pradesh 2270 6500 Nagaland 3000 30000 Mizoram 2600 24000 Tripura 21169.24 2000 Meghalaya 2500 6.03 Sikkim 38 38 Manipur 17000 26986 Northeast (Total) 108577.24 120762.03 in about one year. Adoption of such a strategy would be very useful to increase fish yield from ponds. Some farmers in eastern India adopt a strategy of stocking large numbers of seed, harvesting larger fish, and leaving smaller fish to grow to their potential in the following season. As a general rule, stocking seed of over 50 g of any species at 5000-10,000/ha will result in the best potential yields. Keep water green Green water is essential to increase growth of fish based on natural food produced in the pond (Figure 3). Most carps depend on natural food produced in the pond and this is eaten by fish through filtration or grazing. The Northeast region has abundant vegetation that can be composted in pond corners by creating bamboo fences and dumping the vegetation in such enclosures. Adding manure to a vegetation pit stimulates composting in the aquatic environment and increases primary productivity. Silver carp and tilapia grow rapidly when such an environment is created. Repeated applications are far more efficient than all at once. Apply manure and fertilizers In addition to vegetation, it is useful to add various types of manures (Figures 4 and 5). Farmers generally have cattle and cattle manure is popularly used in fish culture, though its efficacy is far lower as compared to pig or poultry waste and the amount of manure applied could be as much as 30 t/ha per year. The amount required to keep the water green depends on the soil and water quality. In addition to organic manures, chemical fertilizers, such as nitrogen and phosphorous fertilizers, need to be applied. Application of up to 200 kg each of nitrogenous and phosphorous fertilizers would be useful, though farmers now use increased levels in Andhra Pradesh and Punjab to get higher levels of fish productivity. Apply the manure and inorganic fertilizers to keep the water green and prevent over application by carefully monitoring water quality and fish movement. Provide adequate supplementary feed When fish are stocked at higher density, it is essential that they are provided with proper amount of supplementary feed. Farmers use mustard seed oil cake and rice bran to
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