When do you use fishes? An art project near Bob’s apartment consists of cut-outs of fish painted and affixed to a fence. He says they’re (collectively) fishes, and I say fish is correct.
Yes, sometimes it’s ‘fishes’!
Mostly I’d use ‘fish’ for the plural, especially if they’re pretty much undifferentiated (“a boatload of fish”), but if they’re distinct or at least numbered, I’d say ‘fishes’ (“loaves and fishes” or “those fishes that the schoolkids spent so much time decorating and hung on the fence”).
So there!
And BTW, happy 1500! 
Personally, I’d refer to them as “fish”, providing they are the same species.
Fish of varying species or types I refer to as “fishes”, or if referring to all of the varying species of fish life on earth collectively.
From http://www.m-w.com
“Main Entry: 1fish
Pronunciation: 'fish
Function: noun
Inflected Form(s): plural fish or fish·es
Usage: often attributive
Etymology: Middle English, from Old English fisc; akin to Old High German fisc fish, Latin piscis
Date: before 12th century”
"Consider the following examples of English nouns that are said to have two plural forms, taken verbatim from Meiklejohn (1891), a traditional English grammar. The parenthetical explanations are Meiklejohn’s.7 …
fish , fishes (looked at separately), fish (taken collectively)"“Luca Brasi sleeps with the fish” just doesn’t sound right does it?
In this thread from a long time ago, SqrlCub confirms what Stupendous man said. (You have to scroll way down.)