Yeah, it'll be great! I mean, it's not a Koopa, but you've got to use what you can since I'm pretty sure there aren't any Koopas here.

[...Though that would make for an interesting Pokémon...]

It's really tough to raise on its own, so what I did was send it out into battle with my other starter! My other one could do more damage, so I just let the fish get experience while not actually doing anything. It worked like a charm! Just get it to level 20 and it'll turn into one of these beautiful beings!