Locomotion in a Finned Fish

Fish live in water which provides support.

Water is a viscous medium hence offers a lot of resistance to movement.

A fish faces many displacements during locomotion. These are;

(a) Pitching – up and down rocking movements of the head.

(b) Yawing – side to side movements of the anterior parts of the body.

(c) Rolling – rotational movement of the body.

Pitch – Moving up or down

Yaw – Moving to the right or left

Roll – Rotating for belly up.

Adaptations of fish to locomotion in water

• The fish has a streamlined body shape to reduce resistance against movement and enables it to cut through water easily.
• It has an inflexible head that enables it to maintain forward thrush.
• Has scales that overlap and are pointed backwards to allow water to pass over the fish easily without any obstructions.
• The body is covered by mucus to reduce friction during movement.
• It has flexible backbone for attachment of muscle blocks called myotomes that contract and relax to bring about undulating movements.
• Possess a lateral line system along the length of their body that enables it to detect vibrations and changes of pressure in water thus enabling the fish to respond suitably.
• Some possess a swim bladder that provides buoyancy and also enable the fish to adjust its vertical position in relation to depth in the water. When the swim bladder is filled with air, the relative density of the body is lowered so that the fish occupies a higher level in the water. Whereas, when the air is expelled, the relative density rises and the fish sinks to a lower level.
• Have well-developed fins which enhance locomotion in water. The fins enable the fish to maintain balance, steer the fish and to bring about swimming.
• Paired fins are used for maintaining balance, braking, pitching and steering.
• Unpaired fins prevent rolling and yawing.

Types of Fins

(a) Paired fins (pelvic and pectoral fins)

(b)Unpaired fins (dorsal, anal and caudal)

Paired fins

Used for maintaining balance, braking, pitching (upward and downward movement) and steering (changing direction).

Each pectoral fin can be used independently of its opposite member and as such they act as pivots around which the fish can turn rapidly.

When braking, the paired fins are extended rapidly forward at right angles to the body.

Unpaired fins

Prevent rolling and yawing.

Lateral flattening of the fish’s body increase vertical surface area of the body and thus prevent yawing and rolling but instead keeps the fish in an upright position.

The caudal fin propels the fish forward and steers the fish while in motion.

The significance of high tail power

• To enhance thrust for faster propulsion

Describe how myotomes/skeletal muscles of fish bring about locomotion

• Fish have myotomes/block muscles on both sides to the vertebrae which are antagonistic to each other; those on left side contract causing the flexible vertebral column to bend to right side while hose on right side contract causes flexible column to bend on left side; hence swaying movement;