Differences between cartilaginous and bony fishes
Cartilagenous Fishes (Chondrichthyes) :
They are always marine.
Skin is covered by small placoid scales. Endoskeleton is cartilaginous.
Gill slits are not covered by gill covers. Swim bladder is absent.
Tail fin is asymmetrical.
Excretory matter is urea.
They exhibit sexual dimorphism.
e.g., Sharks, rays, skates.
Bony Fishes Osteichthyes :
They may be marine or fresh water.
Skin is covered with large cycloid scales. Endoskeleton is partly or wholly bony. Gill slits are covered by gill covers.
Swim bladder is present.
Tail fin is symmetrical.
Excretory matter is ammonia.
Sexual dimorphism is usually present.
e.g., Labeo, Catla, Hilsa.