Nutrition to Fish

Bikram

Jan 20, 20184 min read

Fish Nutrition

There are usually two types of food available to the fish: natural and supplementary. Natural fish food consists of phytoplankton, zooplankton, periphyton, water plants, etc. produced in the pond itself. Supplementary fish feed is produced outside the pond and supplied to the fish regularly to further increase the amount of nutrients in the pond.

Natural fish food

The natural fish food in the pond largely consists of phytoplankton. The amount of phytoplankton can be increased by the addition of fertiliser to the pond.

Supplementary fish feed

When supplementary feed is thrown into the pond, the fish immediately eat some of it. The uneaten feed will act as an additional fertiliser for the pond. But even in ponds receiving a high amount of supplementary feed, natural feed still plays a very important role in the growth of fish. In general, local organic waste products can be used as supplementary fish feed; the type depends on local availability, costs and the fish species being raised. Typical examples of supplementary fish feed are rice bran, broken rice, breadcrumbs, cereals, cereal wastes, maize meal, Guinea grass, napier grass, fruits, vegetables, peanut cake, soybean cake and brewer's waste.

Some practical guidelines for feeding fish are the following:

1 Feed the fish at the same time everyday and in the same part of the pond. Fish will get used to this and they will come near the surface of the water. This also makes it easier to see if the fish are eating and growing well. Feeding should be done in the late morning or early afternoon when dissolved oxygen levels are high. Fish will have enough time to recover from the high oxygen-demanding feeding activity before nightfall.

2 Do not over feed the fish, as too much feed will decay and use up too much oxygen in the pond.

3 Stop feeding the fish for at least one day before breeding, harvesting or transporting them. The stress from these events causes the fish to excrete waste, which makes the water turbid. In general, fry can be starved for 24 hours, fingerlings for 48 hours and adult fish for about 72 hours. This enables the fish to digest the food completely before stressful events.

Things to care

1. What type of food do farmed fish eat?

Farmed fish and shrimp eat feed that is specially formulated to contain all the essential nutrients they need to keep them healthy and growing and maintain the human health benefits of seafood consumption. The ingredients are formed into pellets, similar in many ways to dry dog food.

2. Do all farmed fish eat the same thing?

No. Fish nutritional needs vary by species. Herbivorous fish eat a feed mixture that may contain plant proteins (e.g., soy, corn), vegetable oils, minerals, and vitamins. In the wild, carnivorous fish such as salmon eat other fish. Therefore, feeds for farmed carnivorous fish (as well as many herbivorous fish) include fish oils and proteins as well as plant proteins, minerals, and vitamins that achieve the nutrition requirements of the fish and offer health benefits to humans. Traditionally, diets for carnivorous fish contained 30-50% fish meal and oil; however, continued research is leading to greatly reduced reliance on these ingredients.

3. Why use fishmeal and fish oil in the diets of farmed fish?

While fish and shrimp don't need fishmeal and oil in their diets, these ingredients have almost a perfect balance of the 40 or so essential nutrients that animals need to be healthy and grow – the same reason that seafood is so good for humans as well.

Fishmeal is a natural and well-balanced source of high-quality protein. As ingredients in aquaculture feed, fishmeal and fish oil supply essential amino acids and fatty acids reflected in the normal diet of fish. Fish oil is a major natural source of the healthy omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty acids are not made by the fish, but become concentrated in fish further up the food chain from the marine phytoplankton (microscopic marine algae and microbes) that do synthesize them.

Through research, we are learning that other combinations of ingredients can achieve the balance of the 40 essential nutrients. Affordable replacement ingredients for fishmeal and fish oil are becoming increasingly common, which is leading to declining percentage on those ingredients in farmed fish diets.

Including ingredients like oils from phytoplankton maintain the nutrient requirements of the final product without depending on fish oil. The economics of using blended oils is improving as fish oil prices rise and the technology to produce phytoplankton (and other replacement ingredients) improves.

4. What are fishmeal and fish oil used for?

Fishmeal and fish oil supply several major industries because they are natural ingredients of high nutritional value. While they have been major ingredients of swine and poultry feeds for many decades, a growing percentage of these resources have been used to manufacture aquatic feeds. This is due to the worldwide growth of aquaculture over the past two decades. Demand for fish oil in the supplement industry also is rising rapidly.

Fishmeal and oil are beneficial components of the diets of farmed fish. Because of this, aquaculture producers have been willing to pay more for these ingredients. As well, substitutes to fishmeal and oil have long been developed for terrestrial animal agriculture, while substitutes for aquaculture are just now coming online. With rising costs for fishmeal and oil, aquaculture producers are developing cost-effective, yet healthful alternatives.