Anatomy of fish
The shape of a fish’s body tells you a lot about its behaviour in the wild. Long stream-lined fish are usually lake or river fish. Being streamlined helps a fish to swim faster in rapid moving waters or open bodies of water such as a large lake. Short or stocky fish are usually from ponds or live near the bed of a river. Side flattened fish usually reside in in slow moving waters with lots of vegatation or roots. The body shape helps these fish swim between plants and reeds. Top flattened fish usually swim on or near the river bed or floor of a pond. Fish with mouth barbels usually swim near the floor of the river or pond and use these barbels to seek food on the murky bottom.
Mouth Anatomy of fish
The shape of a fish’s mouth tells you which part of the water it feeds from. Fish with upturned mouths feed from the water’s surface. Fish with forward pointing mouths feed mostly from midwater. Fish with down pointing mouths feed near the pond floor or river bed. Fish with mouths underneath the head feed off the floor or off algae attached to encrusted rocks.
The scales on a fish’s body provides physical protection from injury. These scales are quite tough and overlap each other to form a tough but flexible armour. The whole of the fish’s scaly body and fins and all body parts are covered in a slimy mucous. This mucous is being continuously secreted by the fish and is used to wash away any bacteria, fungus or virus from invading the body of the fish.
Fins of fish
Fins are used by fish for propulsion, steering, stability and braking. Fins have a secondary function as flags and signals to other fish. Fins when held spread are usually a sign that the fish is healthy, while a fish that is unhealthy will tend to clamp its fins closed.
Some fins are single while other fins are paired. All fins have some purpose.
The single (unpaired) fins are:
- Dorsal fin – This fin is used for stability
- Tail fin – This together with the tail is the main means of forward propulsion
- Anal fin – This is used for stability and in male livebearers is adapted into a reproductive organ.
- Adipose fin – This is found in some species such as the characins or tetras. This fin appears on the top of the fish in between the dorsal fin and the tail fin.
The doubled fins
- Pectoral fins – Pectoral fins lie on either side of the body behind the gills and are attached near the bottom of the fish’s body. They are used for braking, manoeuvring and reversing.
- Pelvic fins – These lie forward of the fishes anus. On most fish these are attched mid body near the bottom of the fish’s body. The pelvic fins helps the fish to rise and descend through the water. They also help the fish turn sharply and assist braking.
The swim bladder in fish is an air filled sac that is within the fish’s body that aids in buoyancy and maintaining the fish’s level in the water. By relaxing or contracting the muscles of the swim bladder a fish can compress the air sac or expand the air sac. When the fish decides to compress the swim bladder it will sink. When the fish expands the swim bladder it will float.
Fish have the same five senses we humans have, plus they also have a specialised sixth sense, the lateral line. The lateral line runs along the middle of the fish from begind the gills to the tail on both sides. The lateral line consists of small pits in the middle of each midline scale. The water filled pits contain small neuromasts which are minute finger shaped structures that contain hairs. When currents enter the pits the neuromasts move, sending a nerve signal to the brain of the fish. This detection of minute changes in flow and water pressure allows the fish to sense its surroundings in a sonar like way. This sense is used in shoaling and detecting minute water currents from prey, other fish or objects. Blind cave fish rely on the lateral line to ‘see’.
Sense of taste in fish
Of course fish don’t have tongues but they do have taste buds in and around their mouths. Many fish also have taste buds all over their body. Many bottom feeding fish have taste buds in their barbels.
Sense of smell in fish
Fish smell through their nostrils. Some fish have two sets of nostrils that allows water to flow through them. Water is pumped into the intake nostril and expelled out of the ottake nostril. The resulting flow of water that passes across receptor cells in the nostril cavity which detects chemical messages and sends signals to the fish’s brain. Fish use their sense of smell to swim away from some smells that may be harmful, such as that of a predator. Or they may swim towards a smell of food or towards potential mate.
Sense of hearing in fish
Although fish do not have ears they do have an internal ear mechanism. Sound actually travels faster through water than through air. Sound travels through water as a series of vibrations. These vibrations travel through the fish’s body mostly undisturbed. However in the fish’s inner ear there are tiny bones called otoliths. Because the otoliths are denser than the surrounding flesh, they vibrate. This vibration is detected by nerves attached to these bones. The nerves then send signals to the brain. In some species sound is amplified by the use of the fish’s swim bladder.
Some fish can make sounds by grinding their teeth or drumming their swim bladder.
Sense of sight in fish
Sight is an important sense for fish as light does penetrate to beneath the waters surface. The eyes of fish have much in common with amphibians, reptiles, birds and mammals. Fish’s eyes tend to be more spherical though. Most species have colour vision and some fish can even see ultraviolet light. Fish focus their vision by moving the lense closer or further from the retina. Most fish do not have binocular vision. However, the hammerhead shark does have a good binocular vision because it has its eyes set far apart but focussed forward.
Sense of touch in fish
Fish do have a sense of touch that spans through their who skin. Scaleless fish such as some catfish have an even better sense of touch.