The feeding of fish is one of the most important aspects of intensive freshwater fish farming (aquaculture). In many such farming systems, feed contributes to almost 60% of the operational cost.
The profitability of the fish farm depends on good feed management, optimal utilisation of the feed by the fish and minimal wastage. There are three important aspects to consider: Feed quality from suppliers Storage facility Feeding procedure If fish receive too little feed or poor quality feed, it may lose weight or die from food deficiency.
Growth will occur only after the fish’s maintenance needs (these include body functions such as breathing and blood circulation) are satisfied. These needs increase with higher water temperatures because the activity of the fish also increases.
Underfeeding will lead to a loss in fish production. Overfeeding is uneconomical and may contribute to poor water quality and production losses. Here are a few guidelines to optimise feeding management and feeding of fish:
Storing of Fish Feed
Do not buy feedstock supplies for more than 4 - 6 weeks and never buy mouldy feedstuff as moulds can produce certain toxins that can be dangerous to fish. Store fish feed on a pallet in a cool dry place with good ventilation. Keep away from walls where moisture might be present. Ensure that the storeroom is free of rodents and other pests that might contaminate feedstocks.Pellet Size and Growth Phase of Fish
Choose the correct grain size and feed type according to the growth phase in the life cycle of the fish. Henk Stander, principal technical manager of the Aquaculture Division of Stellenbosch University, explains that feeds are specific for different freshwater fish species and will also vary according to the age of the fish.
Small fish require more protein in their diet than do larger fish of the same species. Also, feeding the wrong size of pellets can lead to wastage: if the pellet is too big it will not be eaten immediately.
As the pellet softens in the water, the fish will nibble at it as the pellet falls apart. This causes the feed to be wasted as bits sink to the bottom of the dam and certain elements dissolve into the water.
How Much to Feed Fish?
Do not overfeed your fish. Some fish feed manufacturers have online feeding programs that fish farmers can access via their computers or smartphone. These fish feeding programs advise on the correct weight of food to be fed daily, depending on the fish’s weight.
For example, in outside irrigation dams feeding tilapia of 100 - 200 g weight needs 3 g daily, but when grown in covered tanks each fish needs 4,5 g daily, says Henk Stander.
Feeding Procedures in Aquaculture
Maintain correct feeding procedures. This includes feeding time of day, the tempo of feeding, feed distribution in cages (or dam) and frequency of feeding. Observe the fish behaviour before, during and after feeding and adjust feed according to the behaviour.
For example, larger (older fish) are fed twice to three times daily while younger fish are fed more frequently. Even younger fish are fed continuously with mechanical feeders. Observe behaviour and act upon any unfamiliar reactions, e.g. fish eating less than previously.
The addition of carotene, to the diet of rainbow trout, has to be administered 8 - 10 weeks before planned marketing or when fish reach half of the marketable weight, e.g. if fish are marketed at 800 g, fish should receive carotene at 400 g.
Carotene contains plant pigments that contribute to the pink colour of rainbow trout meat. When the water is murky, especially after heavy rains, the visibility decreases and feed has to be given very slowly to make sure all fish are properly fed.
Smaller amounts can also be given several times during the day. Stop feeding when fish response is limited and only start feeding again when response improves. Prescribed food quantities that were lost can always be included in future feeding sessions to bring the fish feeding programme up to date.
By Marinda Louw