1. a fish that has a flexible skeleton made of cartilage is known as a . 2. a row of organs that are sensitive to changes in water pressure is called a . 3. a fish that has muscular pectoral and pelvic fins supported by rod-shaped bones is known as a . 4. movement of the allows some fish to breathe without swimming. 5. a fish that has a bony skeleton and thin, flexible supports in its fins is known as a . 6. the gas-filled sac found in many fishes is called a .

1. chondrichthyan

2 lateral line system

3. lobe fins

4 operculum

5 ray finned fish

6 swim bladder

Explanation:

A fish with a flexible cartilage skeleton is defined as a chondrichthyan

A lateral line system is a column of organs that are sensitive to small change  in water pressure

Fish with strong pectoral and pelvic fins with rod-shaped bones are known as lobe fins

The operculum movement helps certain fish to breathe without swimming.

A fish with a bony skeleton and long, flexible fins is defined as ray-finned fish

A swim bladder is the gas-filled bag used in several fishes.