When can fish and fishes be used as plural?

Here's how to use "fish" and "fishes" correctly:

"Fish"

* As a singular noun: When referring to one fish, use "fish."

* Example: "I caught a big fish."

* As a plural noun: When referring to multiple fish *of the same type*, use "fish."

* Example: "There are lots of fish in the lake."

"Fishes"

* As a plural noun: When referring to multiple fish *of different types*, use "fishes."

* Example: "The aquarium displays many exotic fishes."

In simpler terms:

* "Fish" is usually the plural form unless you're talking about different types of fish.

* "Fishes" emphasizes the variety of fish.

Here are some examples:

* "Fish" (same type): I saw a school of fish swimming by.

* "Fishes" (different types): The scientist studied the different fishes in the coral reef.