Usually fish are fish... even if there are thousands of them. So uncountable. (I'd say thoroughly uncountable if they are all swimming fast!) But fishes is an acceptable variant, often used in nursery rhymes, poetry, astrology, novels set in olden times, and by people who like saying fishes! But I'd guess most people these days just say 'fish' no matter what the number.

It's countable if you are talking about the individual creatures: How many fish can you see? There are some fish in this pond. NB the plural 'fishes' exists, but it is rarely used, except by small children. As with all food, there are cases where a countable noun can be used as an uncountable one. For example, you can buy, cook and eat 'fish' as a general foodstuff. Just like butter, meat, milk, rice and so on are uncountable, so can 'fish' be uncountable. If you cook a large fish, you would serve it and and say 'How much fish do you want? A lot or a little?' This is using 'fish' in an uncountable sense.

Fish (as a meat/food product) is uncountable. As an animal, "fish" is both the singular and plural form. We can say "one fish, two fish", so yes it's countable - replace fish with an uncountable noun and you'll see the difference! There's an interesting reason why it's normal to say "two fish" and not "two fishes", and it's the same thinking that applies to "one sheep, two sheep" and a few other irregular plurals.

FISH in general is non countable However, you may see FISHES in very technical reports or studies that refers to number or species of fish. But day to day speech, it is not countable.