Chapter 32, Problem 8STP

Summary Introduction

Introduction:

Fishes swim with the help of the movement of their tail back and forth. When they stretch their muscles on one side of the body and they relax the muscles on the other side. Fishes push themselves through the water usually with their back fin.

Answer to Problem 8STP

Correct answer:

The correct answer is option (b) paired fins.

Explanation of Solution

Explanation/justification for the correct answer:

Option (b) there are two types of fins in fishes one is paired and the other is unpaired. The paired fins are also called pectorals or pelvic fins whereas the unpaired fins are known as the dorsal or anal fins. Pectoral fins are widely present in almost all the verities of fishes. Paired fins help in free-swimming and guiding the course of the movement.

Explanation for incorrect answer:

Option (a) ctenoid scales in fishes have a comb-like edge similar to what is found in perch fishes. Their overlapping nature allows greater flexibility in movement. They are not helpful to fishes from rolling side to side in the water.

Option (c) placoid scales have spiny and tooth-like projections found in cartilaginous fishes. They do not help fishes from rolling side to side in the water.

Option (d) swim bladder is a gas-filled air bladder in fishes mostly in bony fishes. Its function is to maintain buoyancy, respiration, sound production and pressure fluctuations and do not help fishes from rolling side to side in the water.

Conclusion

Paired fins in the fishes help in rolling side to side in the water.