More reasons (off the top of my head) why it is best not to feed ANY fish:
1. Possible Thiamine deficiency when fed often.
2. Very addictive. Cats that are fed a lot of fish tend to turn their noses up at proteins that are species appropriate.
3. Fish is one of the most common food allergy problems for cats.
4. It isn't a natural prey.
5. Fish caught in the US is sent to China.... and then makes a return appearance in the US.