What is the number of cranial nerves in fish (in $pairs$)?

Fishes having a swim bladder,which does not have direct communication with the exterior and where the resorbent and secretory parts are not sharply separated from one another,are called:

Which of the following features is associated with the aquatic life of fish?

Cod liver oil is extracted from

Which of the following shows direct development?

Why is the tuna fish found in the ocean rarely seen in tropical areas?