A trash fish is a fish that does not have food value. “Trash” is actually a bit misleading, as trash fish can have commercial value and they may play an important role in the ecosystem. Furthermore, some are of interest to sport fishermen. These fish are also known as “rough fish” in some regions of the world.
Definitions of what constitutes a trash fish are quite variable. Over time, attitudes about fish species may evolve. The lobster, for example, was once regarded as fodder for only the most desperate of the lower classes, and is today a delicacy in many regions. Likewise, carp is a trash fish in the United States, but is highly prized in Asia as a food fish and in Europe as a sport fish. These varying attitudes reflect availability of different fish species; more plentiful fish are more likely to be treated as trash fish, and when popular fish decline, people look for substitutes and may turn to fish they previously rejected.
Although such fish are not consumed in the markets where they are caught, they can still have uses. Aquaculture farms need steady supplies of fish and fish is also included in animal fodder. When trash fish are caught, they can be sold to dealers who will process them for sale to farmers, as well as pet food manufacturers. These fish can also be used in the production of fertilizers.
Trash fish can also be important figures in the ecosystem. Even if a fish has no food value, cannot be sold on the market, and is of no interest to sport anglers, it can still have environmental value. Aquatic ecosystems are complex and highly interconnected. A bottomfeeding fish like a lamprey that is not desirable to humans might contribute to water quality and support conditions that allow more popular fish species to thrive. Disrupting the biodiversity of an ecosystem can result in a collapse of a fishery.
Very few fish are regarded universally as trash fish. Culinary tastes vary widely throughout the world and one person's trash may be another person's delicacy. Desperation sometimes spawns creativity and some very famous dishes actually have their origins in finding clever ways to use these types of fish. Species that people may not be interested in eating fresh may be preserved and seasoned in some regions, and the fish sauces of Asia can be produced with less commercially valuable fish species.