about English

Fishes 係指多過一種類o既魚
Fish 可以係一條或多條同種類o既魚

其實一般情況下單數或復數都只用 fish (不論同種或不同種的魚)。
但當要強調不同種的意思時便會用到 fishes。不過，約定成俗，現在已不再計較的了。

但 people 與 peoples 剛相反。當指同族或同一特徵的一群人要用 peoples。

小心啊！

one fish
a fish
two fishes
three fishes
a lot of fishes

There is no different between them.

Fish is a collective word, therefore there should be no ES (fish).
However, Putting ES (fishes) is also acceptable and sensable.