Growth in farmed fish is defined as weight gain during a specific period of time. Fish are cold blooded creatures and their metabolic rate is governed directly by the ambient water temperature. The optimum growth of fish occurs at approximate temperature range of 20 to 35 degree centigrade. At higher temperature than this, a thermal stress occurs, resulting in an excessive metabolic rate, reduced growth, increased oxygen consumption, and greater susceptibility to diseases. If temperature is significantly high than 35 degree centigrade then recommended management strategy should be add fresh water to the pond to reduce water temperature. Growth monitoring of all species are required at intervals of thirty days before final harvest. The desired final product for all species is a minimum of 1.5 kg at harvest.
Feeding of Farmed Fish in Pakistan
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. Four rules should be followed while feeding fish;
- A regular feeding schedule should be followed as infrequent feeding will have little measurable effect on growth. The fish should be fed on daily basis during the warm months.
- The quantity of feed given must be calculated based on the actual sample weight data collected at the end of each month,
- The fish must be fed at the same time each day, and at the same place in the pond. The fish will quickly become accustomed for feeding and will often move to the feeding area as soon as the farmer appears at the edge of the pond. This practice avoids wastage of feed.
- The farmer must carefully observe feeding behavior and determine the extent to which the fish are consuming the feed given.
Supplementary feeds and feed mixtures must be fresh as it quickly disperse and become unavailable to the fish. The fish should be fed slowly, and the farmer must stop feeding when there is no feeding activity especially in cloudy/ rainy days and when temperature is too high or too low.
When Not to Feed Fish: If the fish is showing poor feeding response, or it is not feeling well, or you are planning to harvest fish for sale for sampling or when you are treating pond or when temperature is too high or too low do not feed fish.
Fertilization of Farmed Fish Pond in Pakistan
Fertilization of ponds increases the amount of nutrients available for primary production. Organic and inorganic fertilizers contain nutrients necessary for plant growth. By increasing the production of phytoplankton (the base of the food web), production of other pond organisms also increases. These pond organisms are available food for juvenile fish and crustaceans. There is a direct correlation between phytoplankton production and fish production in fertilized ponds. When the cultured species are in the juvenile stages, increasing primary production with fertilization reduces the need for more expensive supplemental feeds. Two types of fertilizers can be used i.e. organic and inorganic. Inorganic fertilizers are either granular or liquid and can contain a combination of nitrogen (N), phosphorous (P), and potassium (K). Animal manures and vegetation materials are commonly used as organic fertilizers. In agriculture, fertilizer rates for specific crops such as corn or wheat are established by soil testing. This is a well-established procedure for agriculture crops, but fertilizer rates cannot be formulated for individual ponds. A fertilization regime that has been effective in fish ponds can be used to increase production. After filling the pond and prior to stocking, apply 20-20-5 chemical fertilizer at a rate of 22 kg/acre. Follow with two more applications in two week intervals. Continue fertilizer application at the same rate every two to four weeks. Since, water exchange flushes nutrients and phytoplankton from ponds, these ponds may have to be fertilized more frequently. Feeding will add additional nutrients to ponds, possibly reducing the need for continued fertilizer application. When using liquid fertilizers, dilute with water (1:10) and apply around pond edges. In larger ponds liquid fertilizer can be applied throughout the pond with the use of a boat. This fertilization program was developed for low alkalinity freshwater ponds. It cannot be assumed that this standard procedure would be ideal under all circumstances. Farmers may have to generate specific fertilizer procedures for each individual pond.