* Fish: This is the singular form, referring to one individual fish. For example, "I caught a big fish."
* Fishes: This is the plural form, referring to multiple fish. For example, "The aquarium is full of colorful fishes."
However, "fishes" is not always used as a plural. It is sometimes used to emphasize that the speaker is talking about different types of fish, rather than just a number of them.
For example, "There are many different types of fishes in the ocean." Here, the speaker is not necessarily referring to a large quantity of fish, but rather a variety of species.
In general, it's safe to use "fish" as the plural unless you want to specifically emphasize the diversity of fish types.