Q.List three features that characterise bony fishes.

Bony fishes (Class Osteichthyes) are marked out by a bony (ossified) endoskeleton, operculum-covered gills, and an air bladder used for buoyancy, distinguishing them from cartilaginous fishes.

Class Osteichthyes includes the majority of living fishes (e.g., Labeo, Catla, Exocoetus/flying fish, Hippocampus/seahorse) and is characterised by several distinctive features, of which three important ones are:

1. Bony endoskeleton: unlike cartilaginous fishes (Class Chondrichthyes, e.g. sharks and rays), bony fishes have a skeleton made of true, ossified bone, giving strength and rigidity to the body.

2. Operculum-covered gills: each of the paired gills is covered and protected by a bony flap called the operculum, and water is drawn in through the mouth and expelled out through a single opening behind the operculum on each side — unlike cartilaginous fishes, which have separate, exposed gill slits without an operculum.

   …