Earlier quoted context omitted.
I know you are! But if better land management practices is good enough on land, why can't better fisheries management be good enough at sea?
There are many issues, wikipedia seems ok, no time to summarize it, sorry. [ https://en.wikipedia.org/wiki/Fish_farming#Issues ]
I didn't ask about what was wrong with fish farming.
I said: you don't want to cut out ALL agriculture, even though a big part of present agriculture may be unsustainable.
So why do you want to cut out ALL fishing and fish farming? I know the answer is that you're a vegan, but that doesn't cut it if you want to convince those who care about sustainability.