Why cartilaginous fishes have to swim constantly?

Cartilaginous fishes are

Cartilaginous fishes are

Cartilaginous fishes are

Cartilaginous fishes do not have

Cartilaginous fish have gill covers.

Assertion :- Scoliodon (Dog fish) have to swim constantly to avoid sinking. Reason :- It does not have air bladder.

Due to the absence of air bladder, fishes belonging to the class Chondrichthyes have to swim constantly. How important is the presence of air bladder in these fishes?

Scales in cartilaginous fishes are

Cartilaginous fishes belong to the class

Cartilaginous fishes belong to the class