Fishbase

As from its name Fishbase is a database containing the data of over 31,000 species of fish accompanied, in most cases, the relevant photos.
The home page interface is, at least, essential:not more than a form to enter search parameters:

simple and effective.

It 'available in all major languages of the world and is definitely an essential tool for anyone breeding fishes.
Unfortunately, the main server is often unavaillable for network overload and I suggest to bookmark all mirrors addresses to find most available one.