Farmed fish are usually fed on a combination of pellets made from ground fishmeal or vegetable matter. Different species of fish or shellfish require different types of feed. For example, freshwater species are more likely to consume plant products, while saltwater species may require animal proteins to survive. Fish farms have come under some scrutiny over how much wild fish protein is needed to feed captive stocks.
Carnivorous fish such as salmon, sea bass, cod and trout are fed on a diet of pellets made from pulped fish. Species such as sardine, anchovy, mackerel and shrimp are all used to create fish farm food. Herring is a common fish used in creating fish pellets for salmon, according to Stanford University. In some fisheries, particularly organic ones, fishmeal from bycatch or discarded fish is used to fishmeal.
Some farmed fish require little or no meat in their diet. These are often freshwater varieties such as catfish, tilapia and carp. Tilapia is one of the most-farmed species in the world with around 2.3 million metric tons produced each year, according to the World Wildlife Fund. Food pellets for vegetarian fish often consist of corn, soy and grain products. However, demand for fish is so high that some farms have started adding fishmeal to the diet of vegetarian fish in an effort to promote faster growth, according to Stanford University.
Carnivorous farmed fish consume great amounts of wild fish protein. However, there is some controversy over the efficiency of this process. For example, it takes around five pounds of smaller fish to create one pound of farmed salmon, according to Stanford University. Nearly all of the fish used for feed are captured in the wild. This can create problems of bycatch, population decreases and a knock-on effect for other species in ocean ecosystems that depend on small fish to eat.
Additives and Antibiotics
Some types of fish farm food contain substances added to either alter the pigment of the fish or offer some medicinal benefit. For example, salmon feed may include the additive canthaxanthin or mashed shrimp shell to encourage a pinker tone to the flesh, according to the BBC. Some farms mix pesticides or antibiotics in with fish food to prevent disease or rid fish or parasites such as sea lice. This can have the unintended side-effect of poisoning local water and land, according to an LA Times article.
Nutrition and Pellet Type
Feed should match the full nutritional requirements of the farmed fish species. Including all valuable nutrients can help prevent diseases and promote fast, healthy growth, according to the College of Agriculture at the University of Kentucky. The size and type of feed also differs depending on the type of fish and their age. For example, fry are usually fed on flakes or crumbled fish meal, while older fish may consume larger hard pellets. Whether the pellets sink or float on the surface should depend on the fish's natural method of feeding. For example, catfish are more commonly bottom feeders, while tilapia more often take food from the surface.