Water is the most essential component of inland fish farming. Normally two sources of water are preferred i.e. tube well and Irrigation canal water. Irrigation water comes from the entire catchments area of the drainage, thus it carries high loads of silt, and is subject to change in environmental conditions and water quality ( temperature changes, rainfall silt loadings, alkali salt runoff, etc.) it may also carry a large number of trash/carnivorous fish. In case of selecting irrigation water, proper filtration method must be used for obtaining the desire quality.
The water quality of the tube well should be analyzed, oxygenation is main problem with the tube well water, and arrangement must be made for oxygenation of water that can be accomplished by installing air blowers. Thus temperature and dissolved oxygen should be tested at the site. A sample should be taken in one liter bottle capable of being sealed and transported immediately to a lab for further examination analysis, tests of the total alkalinity, pH, nitrogen, salinity and total dissolved solids are required. The key water quality parameters for pond production are temperature, oxygen, pH, alkalinity, hardness and nitrogenous wastes.
Oxygen levels higher than 5 mg/L are good for eggs, larvae, fry and fingerlings. When dissolved oxygen levels are low, fish start gulping air at water surface. Even adult fish will perform better when the dissolved oxygen levels are adequate. Oxygen levels of 0 – 1.5 mg/L can be lethal especially if exposed for long periods. At 1.4 – 5 mg/L-fish survive, but reduced feed intake, higher FCRs, slow growth, stress, and increased susceptibility to disease has been observed. Gas bubble trauma occurs when the water is supersaturated to levels of 300% and above. During day, oxygen deficiency may not be problem in well fertilized ponds due to oxygen production from phytoplanktons and water perturbations but problem may occur when this process reverses at night so some sort of artificial aeration will be required during night or even during day if stocking densities are high. Daily monitoring of oxygen especially during hot and humid days is very important.
Fish are cold blooded animals. Their rate of metabolism is directly influenced by water temperature. Rate of breaking down of wastes in pond and dissolution of chemicals is faster in warmer waters. Temperatures at 26 oC or higher affects solubility of oxygen in water. If the temperature is below 20 oC there is reduced feed intake which stops growth. At lower or higher temperatures than optimum, feed intake is lower and FCRs are higher. At extreme temperatures fish is more susceptible to disease and sometimes death ensues.
Water pH Level
It affects the solubility and chemical forms of various compounds. The pH range from 6.5 to 9 is acceptable, below 4 is called ‘Acid Death Point’. Fish can survive from 4 – 6.0 but remain stressed, growth is slow, there is reduced feed intake and FCRs are higher. Low pH indicates high levels of dissolved carbon-dioxide, hence, pH values from 9 – 11 are stressful for fish and considerably reduces growth rate. The pH value above 11 is ‘Alkaline Death Point’.
Alkalinity and Hardness
In combination, alkalinity and water hardness influence the buffering capacity of the pond water. Hardness is composed mostly of calcium and magnesium, which affect the physiological condition of the fish. Alkalinity also controls the amount and form of carbon-dioxide in water. Alkalinity > 20 ppm, hardness > 20 ppm, total alkalinity and total hardness above 60 ppm is desirable. Well buffered water will minimize diurnal fluctuations in pH.
Ammonia Nitrogen (TAN)
Ammonia occurs in both toxic (ammonia) and nontoxic form (ammonium) depending on the pH of the water. Toxic ammonia more than 0.3-0.5 is not acceptable. The proportion of TAN in the form of ammonia tends to be higher as the pH of the water increases above 7. The fish become susceptible to pathogenic attacks and fail to eliminate ammonia from their blood because there is too much ammonia already in the water. Ammonia is excreted by fish as a byproduct of protein metabolism primarily through their gills. High concentrations of ammonia in water reduce the ability of the gills to do so.
The fundamental objective of feeding fish is to get maximum growth, optimum yield, good health, ultimately optimizing profits which are impossible without the provision of quality feed in sufficient quantities. Presently commercial fishes are cultured at both natural and artificial feeds so feeding methods differ and are adapted according to the particular fish species requirements. Since natural feed is cultured in pond before introduction of fish and /or after stocking to cater its daily requirements, hence, feed once produced is not stored and is fed to fish immediately otherwise it will lose its palatability and nutritional efficacy. Artificial feeds, however, sometimes supplement the existing natural feed or sometimes work alone to cater all the nutritional requirements of fish. Pelleted floating artificial feed is always preferable with few exceptions.
Concentration of protein in feed decreases with increase in fish size; higher protein percentage is required for smaller fish while lower for bigger fish. Proper pelleting of feed is of key importance for ideal water quality, maximum output with minimum pollution. Nutrient requirements and feed formula can also vary in different environments and according to the availability of feed ingredients. In a well-managed pond enough food will be produced to permit the moraka, rohu and thaila to attain marketable size in a prescribed growth period. All species will accept supplementary feeds and additional weight gain may be realized, but the bottom and water column feeding species (Rohu and Moraka) may receive the most benefits, especially if the amount of organic material in the pond is limited.
Feeding of Grass carp
Natural diet of grass carp (about 30 mm) is macro vegetation. Aquatic macro vegetation in pond is limited – supplementary feed is provided (Rice barn/ polish/ oil seed cake etc.)
Common Method = Cut grass and feed it directly
40 Kg of fodder for every 1.0 Kg of gain in weight Fodder should be placed in the same area / one morning feeding. Uneaten food should be removed it can cause Oxygen depletion