Most fish are torpedo shaped, with rounded nose, a thicker middle and a tapered tail. The shape of the fishes body is very important to how it swims. Fish with long thin bodies are good swimmers; fish with shorter bodies can manuever turns more quickly. In the wild the shape of a fish has a lot to do with how it hunts its prey. The more active fish usually have a more steamlined shape with a forked tail and are faster swimmers. They are the type that will actively pursue prey. Fish that have a "sit and wait" type hunting style are usually thick, deep, heavy bodied fish that have large round tail fins to push them forward more quickly. They will wait for its prey to come close, then dash out quickly to attack it.
The Head of the fish has the mouth, nostrils and gill cover. The gills, found under the gill covers, allow the fish to breathe. As water moves over the surface of the gills, oxygen is absorbed, like lungs in land animals.
Scales protect the fish like skin or hair does animals. They overlap like shingles on a roof so that the skin of the fish is not exposed. As a fish grows, their scales produce "rings" much like a tree, and that is one way scientists can tell how old a fish is. Most fish get extra protection from a layer of slime that covers their scales. This slime helps them move through the water better, and keeps germs etc. off of the fish's skin.
The Lateral Line is how the fish "hears". It is sensitive to pressure, vibration, movement and sound and lets the fish know what is in the water around them.
The Fins help the fish swim. The large muscles of the body actually do most of the work, but the fins help with balance and turning. In some fish the fins are large and spiney and help protect the fish from its predators.
You should try to get familiar with the external anatomy of the fish. The names of various fins and parts of the body are used in the description of the different species.
The fins are made up of stiff rays covered by skin. Some may be jointed and some separate near the edge of the fin. In certain fish, some of the rays supporting the fins are bony, stiff, and unjointed. They are referred to as spines. Almost half the fin rays in the Dorsal fin of Cichlids are bony spines. So the front (Anterior) portion of such a fin is called the Spiney Dorsal and the rear (Posterior) portion is called the Soft Dorsal. In Gobies and some other species the Spiny Dorsal and the Soft Dorsal are completely separated and form two distinct Dorsal Fins. The number of rays in the fin is also used in classification.
Each fin on a fish is designed to perform a specific function. I will list them here.
Dorsal fin- Helps in keeping the fish stable while swimming.
Ventral fin- Helps in keeping the fish stable while swimming.
Caudal fin- This fin for most fish is the main fin for propelling.
Anal fin- Also used for stability in swimming.
Pectoral fins- Used for propelling and side to side movement.
Adipose fin- Adds Stability while swimming.
The skin of fish is divided into two layers, the Epidermis (outer) layer and the Dermis. The Epidermis is made up of Epithelial cells, arranged one above the other. These cells are constantly shed and replaced with new ones. The inter space between the Epithelial cells are slime cells which produce mucus that form the very important protective covering, we know as the slime coat. The Dermis lies under the Epidermis and serves many useful purposes.
The Dermis of the skin is made up of connective Fibroblasts, Collagen and blood vessels. The scales of a fish lie in pockets in the Dermis and come out of the connective tissue. Scales do not stick out of a fish but are covered by the Epithelial layer. The scales overlap and form a protective flexible barrier capable of withstanding blows and bumping. There are two main types of scales, both are round, but in one the edges are serrated and the other are completely smooth. In the Mailed Catfish the scales are replaced by bony plates. In some other species there are no scales at all.
Pigment (color) cells
The many pretty colors and patterns seen in fish are produced by cells in the Dermis. The cells are named for the pigment they contain.
Melanophores Brownish-Black pigment called Melanin.
Erythrophores Red pigment.
Xanthophores Yellow pigment.
Iridophores Contain crystals which refract and reflect light, given many fish their metallic look.
Fish can change color from one moment to the next. This is caused by the movement of Melanin grains within each cell. When dispersed, they Absorb more light and the area of the fish darkens. when tightened the fish goes pale.
Respiration is carried out by means of gills located under the gill covers. The walls of the Pharynx is perforated by five slit-like openings. The tissue between the slits is called the Gill arch, so on each side of the fish there are five Gill Slits and Four Gill Arches. On the Gill Arches are mounted the actual Gills, a delicate system of blood vessels covered by a very thin Epithelium through which the gaseous exchange takes place.
The lateral line consists of a series of scales, each modified by a pore, which connects with a system of canals containing sensory cells and nerve fibers. It runs in a semi line from the gills to the tail fin. It can be easily seen in fish as a band of darker looking scales running along the side. The Lateral line has shown to be a very important sensory organ in fish. It can detect minute electrical currents in the aquarium water. It can also function as a kind of echo location process that helps the fish identify its surroundings.
Other senses in fish
Fish have the five senses man has as well as the Lateral line. In fish the importance of each sense is different than to people. They are briefly described below.
Sight vision underwater poses many special problems. The most significant is the small amount of light available in all but the uppermost layers of water. Vision under water is limited to a few yards at best and fish do not use this as one of their primary senses.
Smell In most fish the sense of smell is highly developed and is probably used more in the location of food than sight.
Hearing It has been shown that fish can hear, but its full function is still not understood.
Taste Taste buds in fish are located in the mouth and also in the skin covering the head, body fins, Barbels and lips. Its entirely probable that fish can taste food well before it enters their mouth.
Touch Fish also have elevated tactile sense and is shown none better than in certain catfish who use their Barbels as extentions of their body.
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