While farmed fish and shellfish can supplement our seafood supply, they can’t replace the variety and abundance of seafood from the wild. Some fish farms still depend on wild populations to supply eggs or juveniles that the farmers raise for market. Many fish farms also depend on wild fish, like sardines or anchovies, as food for the farmed species.
Some Fish Are Carnivores
Every year, millions of tons of wild fish, like sardines and anchovies, are caught and processed into fishmeal and fish oil, which is used to make feed for farm-raised species. Some of these species, like salmon—one of the most popular farmed fish in the world—require over a pound of wild fish for every pound of weight they gain. Tuna requires over 15 pounds of feed for every pound it gains.
Developing Alternative Diets
There’s good news: not all fish are carnivores. Some, like catfish and tilapia, can be raised on diets with very little or no fishmeal or fish oil. Shellfish (like mussels and oysters) are another good option. These animals feed by filtering plankton out of the water and need no supplemental food.
Ranching Wild Fish
Some fish farms operate as “ranches.” Instead of raising fish from eggs, they take large numbers of fish from the wild and grow them for eventual sale. Not only do these farms still rely on wild populations, in some cases the fish they take are still juveniles. For example, young eels are caught and then farmed to supply unagi to sushi bars. Similarly, young bluefin tuna are ranched for highly-profitable but resource-intensive industry. This practice has contributed to the depletion of wild stocks of both of these species.