In most cases the plural of "fish" is just "fish". But when we talk about a number of groups of fish, we often say "fishes".
So, you might hear phrases like:
"All the fishes in the sea." meaning all the different types of fish.
"The fishes of Texas." meaning the different types of fish found in Texas.
Similarly, you might hear the word "peoples" meaning a number of groups of different people. The phrase "peoples of the world" means all the different groups of people around the world.
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