How's this list:
Fastest Fish:
Sailfish, Istiophorus platypterus: 68.18 mph
Mako Shark, Isurus oxyrinchus: 60 mph
Marlin, Tetrapturus sp. 50 mph
Wahoo, Acanthocybium solandri 48.5 mph
Bluefin Tuna, Thunnus thynnus 43.4 mph
Blue Shark, Prionace glauca 43 mph
Bonefish, Albula vulpes 40 mph
Swordfish, Xiphius gladius 40 mph
Slowest Fish:
Sea Horse 0.01 mph
from
http://oceanlink.island.net/records.html
Oh, and let's not forget the mammals:
Fastest Swimming Baleen Whale (short distance)
Sei Whale, Balaenoptera borealis: 35 miles per hour in short bursts
Fastest Swimming Dolphin
Dall's porpoise, Phocoenoides dalli, recorded at 56 km/hr
Killer Whale, Orcinus orca , recorded at 56 km/hr
Common Dolphin, Delphinus delphis - 37 miles per hour while riding ship's bow waves, 28 miles per hour in open water