actually there is a word fishes.. it's just used differently, same as "people". It's always singular when you refer to a group, but for several different civilizations, (or species of fish) you use peoples (or fishes), but that's not at all relevant 

This is kinda funny, the only problem i see is that the big guy looks like he's vibrating rather than floating.  I've never animated before, but I'm pretty sure that adding more frames would make it smoother.. or slowing the animation? But I like how fast the little fish swim out of his mouth, so I'd try just adding more frames.
I love that evil smile! hehe