Fish feed used in the aquaculture industry has frequently been a source of controversy for its high usage of fish meal and fish oil. Fish meal and fish oil are created using small, open-ocean (pelagic) fish such as anchovies, herring, menhaden, capelin, anchovy, pilchard, sardines, and mackerel. These fish are harvested by the wild fisheries industry. Many believe it is impractical to continue this practice, however, fish meal and fish oil have the optimized ratio of the over 40 essential nutrients required in many carnivorous species' diets. The aquaculture industry has acknowledged these concerns and responded by investing in research for alternative feed sources. These includes using soybeans and corn as protein sources in feeds. Based on comparative studies, diets based on plant protein have been shown to be as successful as diets based on fish meal and fish oil.