KCSE 2010 Q8. Describe how a finned fish such as Tilapia moves in water. (20 marks)

The following describes how a finned fish such as Tilapia moves in water.

v     Water is denser than air. The density of water supports fish and provides a medium in which it swims.

v     It has a streamlined body; reducing resistance, thus easily swims in the water.

v     The scales overlap pointing backwards allowing water to pass over the fish without obstruction. Mucus is also secreted over the scales reducing friction during movement.

v     They have a flexible backbone onto which segments of muscle blocks, myotomes, are attached. The muscles contract and relax bringing about undulating movements.

v     The fish have fins that help in steering and balancing fish during swimming.

v     The pectoral and pelvic fins are paired. They are used for braking, steering and

v     balancing the fish.

v     They control pitching i.e upward and downward movement.

v     The dorsal and ventral fins are unpaired. They prevent rolling' i.e. turning of the body about its axis and yawing i.e. lateral deflection of the body during swimming.

v     The caudal fin is unpaired and propels the fish forward and steering.

v     In the fish there is a swim bladder that is air filled cavity which regulates buoyancy. When it is filled with air, the fish floats as the density decreases. When air in swim bladder is released, density increases and swims at tower levels.

v     The fish have a lateral line that increases sensitivity in water. It helps the fish to escape from predators.