Note that with any pet animal, it's perfectly okay to use "boy" and "girl" -- because, you know, pets are like children. So you can say "girl cat" for кошка, and "boy dog" for пёс, etc.
However, if you're talking about wild animals, it's much better to use "male" and "female" -- if you say "boy shark" or "girl elephant" or whatever, it sounds a bit childish (or foreign).