It's an entirely different planet. Therefore it stands to reason that regardless of the indiginous earth life we might seed on that planet, it would likely start producing it's own unique organisms after time as well. Though it has to be said that it would take
quite some time for that to happen, so Aqua-Cats are more likely to be engineered/ cross-bred variants of Earth-Cats.
Personally however, I'm just of the opinion that Aria looks the way he does because it's funny
Who needs science in a show like this, eh?