Many people seem reassured by reading that the fish they are eating is taken from 'sustainable sources'. It now appears, following DNA tests that some of the so-called 'rock salmon' sold in UK fish and chip shops is actually sourced from endangered (and protected) shark species
(https://www.theguardian.com/environment/2019/jan/31/fish-and-chip-shops-are-selling-endangered-sharks-dna-tests-prove). Even some of the sharks fins sold to make sharks fin soup is some endangered species. It seems that DNA studies are likely to reveal that much of what we eat, isn't what we think it is.