World's Smallest Fish.

Maurice Kottelat, Tan Heok Hui and colleagues discovered the world's smallest fish in an acidic peat swamp in Indonesia.

Mature females of the Paedocypris progenetica, a member of the carp family, only grow to 7.9 millimeters (0.31 inches) and the males have enlarged pelvic fins and exceptionally large muscles that may be used to grasp the females during copulation...

Now why doesn't that last bit surprise me...

http://www.livescience.com/animalworld/060125_ap_smallest_fish.html