The word ‘Fish’ can be used as -

Fish - Noun টি বাক্যে ব্যবহারের উপর ভিত্তি করে Singular/plural অথবা Countable/Uncountable যে কোনটিই হতে পারে।

Singular Noun: Sanjay caught the biggest fish I've ever seen. 
Plural Noun: (Fish or Fishes)
- Several large fish live in the pond.
- Three fishes have been segmented in these images.

Countable Noun: How many fish live in the pond?
Uncountable Noun: We had fish for dinner.

Source: Cambridge Dictionary