Overview
Fishes are cold-blooded aquatic vertebrates with gills at all stages of their lives and limbs (when present) in the shape of fins. They inhabit every aquatic habitat at sea and many of the freshwater systems on land, and can be found at some of the deepest trenches to the highest alpine lakes on the planet.
Fishes are by far the most specious, diverse and abundant vertebrates on our planet, with over 30,000 known species belonging to 538 families and 63 orders. Fishy forms range from lancelets, hagfishes, lampreys, sharks, rays and ghostsharks a vast variety of bony fishes.
Three broad groups of fishes are recognised:
1) Jawless fishes (Agnatha)
2) Sharks, rays & chimaeras (Chondrichthys)
3) Bony fishes (Osteichthyes, Teleostei)