What are the valuable commercial fish and rational use measures?

There are a very large number of commercial fish. They are used by humans for their own purposes. It is mainly about getting meat and caviar. Also, fish oil is mined. The most common in us are herring, cod, trout, sea bass and many others. Fish can be caught in freshwater or salt water, or grown on special fish farms. Basically, such farms are needed to obtain caviar, since fish on farms do not need to be killed to obtain valuable caviar, as many poachers do.