In the world of marine biology, fishes are primarily classified based on the material that makes up their skeleton. The two most prominent classes are Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes).
Key Differences at a Glance
| Feature | Chondrichthyes (Cartilaginous) | Osteichthyes (Bony) |
| Skeleton | Made of cartilage | Made of bone |
| Examples | Sharks, Rays, Skates | Salmon, Goldfish, Tuna, Seahorses |
| Mouth Position | Usually ventral (underside) | Usually terminal (at the tip) |
| Gills | 5–7 pairs; no gill cover (operculum) | 4 pairs; covered by an operculum |
| Swim Bladder | Absent (they must swim to stay afloat) | Present (helps maintain buoyancy) |
| Scales | Placoid scales (tooth-like) | Cycloid, Ctenoid, or Ganoid scales |
| Fertilization | Mostly internal | Mostly external |
Examples:
Chondrichthyes :
Sharks: The most famous members, including the Great White, Hammerhead, and Whale Shark.
Osteichthyes:
Ray-finned Fishes: This includes almost all familiar fish, like Salmon, Trout, Tuna, Cod, Seahorses, and even the tiny Betta fish.
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