(though she got it from someone else, I don't know who)
Merely ending in "fish" is in suffishient :)
rainbow trout / eelpout
gar / char
bass / wrasse
jawfish / sawfish
bonefish / stonefish
Edit: batfish / catfish
... and another late addition: toby / goby
[Feb 2016] shad / scad
First one is from Valerie, the rest are me & Alice. Can you think of another?
Edit - More from the comments...
aruana / piranha
cory / dory (which Alice and I thought of, but then thought "dory" wasn't a type of fish)