DICA ANTES DO QUIZ:

Fruit is usually uncountable:

- I love fruit.
- She likes fruit.

Fruit is used as a countable noun when talking about particular types of fruit:
- They grow mainly sweet fruits.
- They grow mainly citrus fruits.

So, both fishes and fruits are plurals, but not the most common ones.
They both are used to refer to species, but not used so commonly in everyday conversations.

It may sound strange if you use them incorrectly.