Movement in Animals and Plants — BIOLOGY STD 7 — Question

Muscles, fins and tail help the fish to swim. Fish have two types of fins – paired and unpaired. Pectoral and pelvic fins are paired fins. Dorsal, ventral and tail fins are unpaired fins. Fish can move on either side of the backbone with the help of fins. The muscles contract from one side and expand on other side. This moves the body of fish from side to side in a zig-zag pattern. As the tail fin moves along with the body in a zig-zag pattern, it pushes against the water. This force pushes the fish’s body forward.
The paired fins help the fish to swim in upward and downward direction. They also help to slow down or stop. The balance of the body while swimming is maintained by the unpaired fins. The streamlined body (narrow in front and broader in middle) also helps them in their movement in water. This reduces water resistance and enables the fish to glide along the water.