What fish are you allowed to eat and what are you not allowed to eat ??

I've started to buy us fish but want to make sure I am buying the right kind of fish. With being brought up in the UK most fish here is odd to me. I'm used to things like cod, plaice, haddock etc

I brought some Basa and we had it tonight for tea then i started to worry was it ok to eat. Too late to worry as i had already eaten it before i thought about it.