Question

Endoskeleton of fishes are made up of cartilage and bone. Classify the following fishes as cartilaginous or bony: Torpedo, Stingray, Dog fish, Rohu, Angler fish, Exocoetus.

Answer 1

Hint: Cartilaginous fishes are different from bony fishes by their endoskeleton. The skeleton of cartilaginous fishes is primarily made up of cartilage whereas the skeleton of bony fishes are entirely made up of bone. Cartilaginous fishes are found mainly in marine environments whereas bony fishes are found in both freshwater and saltwater environments.

Complete answer:
1. Cartilaginous fishes: Torpedo, sting ray and Dog fish belong to the category of cartilaginous fishes.
The following are some of the characteristics of cartilaginous fishes:
Their exoskeleton is made up of placoid scales.
The tail fin has an unequal upper and lower lobe.
Fertilization happens internally, that is inside the body.
Absence of swim bladder.
2. Bony fishes: Rohu, Angler fish, Exocoetus come under the category of bony fishes. Some of the characteristics of bony fishes are as follows:
Cycloid scales make up their exoskeleton.
The tail fin appears outwardly symmetrical.
Fertilization occurs externally, that is outside the body.
Presence of swim bladder.

Additional information:
Cartilaginous fishes belong to the class Chondrichthyes. Bony fishes belong to the class Osteichthyes. All cartilaginous fishes are carnivores, whereas bony fishes have a variance in their feeding habits. They can be herbivores, carnivores, or omnivores.

Note:
Buoyancy is essential for fishes because it helps them to maintain their position in the water. Even though swim bladder is absent in cartilaginous fishes, the fishes maintain stable buoyancy due to the lighter weight of their endoskeleton. The cartilaginous fishes come to the surface of the water to take in air which also helps them maintain buoyancy.