If the "low fruit" species are fished out, then the more remote, less desirable species are likely to be targeted. There is also the danger of damaging the eco system, or at least destabilizing it in unpredictable ways.
There is also a lot of deception in the naming of fish. Fish species are renamed in order to make them sound like fish we are used to. The fish species you get in British Fish and Chip shops are rarely the species our parents and grandparents ate