Fish
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Fish
Admin Mon Dec 10, 2007 2:10 pm
Fish are aquatic vertebrates that are cold-blooded, covered with, and equipped with two sets of paired fins and several unpaired fins.
The term"fish" is most precisely used to describe any non-tetrapodchordate,i.e., an animal with a backbone that has gills throughout life and has limbs, if any, in the shape of fins. Unlike groupings such as birds or mammals, fish are not a single clade but a paraphyletic
collection of taxa, including hagfishes, lampreys, sharks and rays,ray-finned fishes, coelacanths,and lungfishes.
A typical fish is cold-blooded; has a streamlined body that allows it to swim rapidly; extracts oxygen from the water using gills or an accessory breathing organ to enable it to breath atmospheric oxygen; has two
sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin,
and a tail fin; has jaws; has skin that is usually covered with ; and lays eggs that are fertilized internally or externally.
Digestive system
The advent of jaws allowed fish to eat a much wider variety of food,
including plants and other organisms. In fish, food is ingested through the
mouth and then broken down in the esophagus. When it enters the stomach, the food is further broken down and, in many fish, further processed in fingerlike pouches called pyloric caeca. The pyloric caeca secrete digestive enzymes and absorb nutrients from the digested food.
Organs such as the liver and pancreas add enzymes and various digestive chemicals as the food moves through the digestive tract. The intestine
completes the process of digestion and nutrient absorption.
Respiratory system
Most fish exchange gases by using gills that are located on either side of the pharynx. Gills are made up of threadlike structures called filaments. Each filament contains a network of capillaries that allow a large surface
area for the exchange of oxygen and carbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gill filaments. The blood in the capillaries flows in the opposite direction to the water, causing counter current exchange. They then push the oxygen-poor water out through openings in the sides of the pharynx.
Some fishes, like sharks and lampreys, possess multiple gill openings.
However, most fishes have a single gill opening on each side of the body. This opening is hidden beneath a protective bony cover called an operculum.
Circulatory system
Fish have a closed circulatory system with a heart that pumps the blood in a single loop throughout the body. The blood goes from the heart to gills, from the gills to the rest of the body, and then back to the heart. In most fish, the heart consists of four parts: the sinus venosus, the atrium, the ventricle, and the bulbus arteriosus. Despite consisting of four parts, the fish heart is still a two-chambered heart
Excretory system
As with many aquatic animals, most fish release their nitrogenous wastes asammonia. Some of the wastes diffuse through the gills into the surrounding water. Others are removed by the kidneys, excretory organs that filter wastes from the blood. Kidneys help fishes control the amount of ammonia in their bodies
Sensory and nervous system
Central nervous system
Fish typically have quite small brains
relative to body size when compared with other vertebrates.
Sense organs
Most fish possess highly developed sense organs. Nearly all daylight fish
have well-developed eyes that have color vision that is at least as good as a human's. Many fish also have specialized cells known as chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears in their heads, many fish may not hear sounds very well. However, most fishes have sensitive receptors that form the lateral line system. The lateral line system allows for many fish to detect gentle currents and vibrations, as well as to sense the motion of other nearby fish and prey. Some fishes such as catfishes and sharks, have organs that detect low levels electric current. Other fish, like the electric eel, can produce their own electricity
Reproductive method
Over 97% of all known fishes are oviparous,that is, the eggs develop outside the mother's body.Ovoviviparous fish are ones in which the eggs develop inside the mother's body after internal fertilization but receive little or no nutrition from the mother, depending instead on the yolk.
Some species of fish are viviparous. In such species the mother retains the
eggs, as in ovoviviparous fishes, but the embryos receive nutrition from the
mother in a variety of different ways.
Bichir
All species occur in freshwater habitats in Africa, mainly swampy, shallow floodplains and estuaries. They have rudimentary lungs, which allow them to obtain oxygen from the air when in poorly oxygenated waters by swimming quickly to the surface and back to the bottom.
A typical fish is cold-blooded; has a streamlined body that allows it to swim rapidly; extracts oxygen from the water using gills or an accessory breathing organ to enable it to breath atmospheric oxygen; has two
sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin,
and a tail fin; has jaws; has skin that is usually covered with ; and lays eggs that are fertilized internally or externally.
Digestive system
The advent of jaws allowed fish to eat a much wider variety of food,
including plants and other organisms. In fish, food is ingested through the
mouth and then broken down in the esophagus. When it enters the stomach, the food is further broken down and, in many fish, further processed in fingerlike pouches called pyloric caeca. The pyloric caeca secrete digestive enzymes and absorb nutrients from the digested food.
Organs such as the liver and pancreas add enzymes and various digestive chemicals as the food moves through the digestive tract. The intestine
completes the process of digestion and nutrient absorption.
Respiratory system
Most fish exchange gases by using gills that are located on either side of the pharynx. Gills are made up of threadlike structures called filaments. Each filament contains a network of capillaries that allow a large surface
area for the exchange of oxygen and carbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gill filaments. The blood in the capillaries flows in the opposite direction to the water, causing counter current exchange. They then push the oxygen-poor water out through openings in the sides of the pharynx.
Some fishes, like sharks and lampreys, possess multiple gill openings.
However, most fishes have a single gill opening on each side of the body. This opening is hidden beneath a protective bony cover called an operculum.
Circulatory system
Fish have a closed circulatory system with a heart that pumps the blood in a single loop throughout the body. The blood goes from the heart to gills, from the gills to the rest of the body, and then back to the heart. In most fish, the heart consists of four parts: the sinus venosus, the atrium, the ventricle, and the bulbus arteriosus. Despite consisting of four parts, the fish heart is still a two-chambered heart
Excretory system
As with many aquatic animals, most fish release their nitrogenous wastes asammonia. Some of the wastes diffuse through the gills into the surrounding water. Others are removed by the kidneys, excretory organs that filter wastes from the blood. Kidneys help fishes control the amount of ammonia in their bodies
Sensory and nervous system
Central nervous system
Fish typically have quite small brains
relative to body size when compared with other vertebrates.
Sense organs
Most fish possess highly developed sense organs. Nearly all daylight fish
have well-developed eyes that have color vision that is at least as good as a human's. Many fish also have specialized cells known as chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears in their heads, many fish may not hear sounds very well. However, most fishes have sensitive receptors that form the lateral line system. The lateral line system allows for many fish to detect gentle currents and vibrations, as well as to sense the motion of other nearby fish and prey. Some fishes such as catfishes and sharks, have organs that detect low levels electric current. Other fish, like the electric eel, can produce their own electricity
Reproductive method
Over 97% of all known fishes are oviparous,that is, the eggs develop outside the mother's body.Ovoviviparous fish are ones in which the eggs develop inside the mother's body after internal fertilization but receive little or no nutrition from the mother, depending instead on the yolk.
Some species of fish are viviparous. In such species the mother retains the
eggs, as in ovoviviparous fishes, but the embryos receive nutrition from the
mother in a variety of different ways.
Bichir
All species occur in freshwater habitats in Africa, mainly swampy, shallow floodplains and estuaries. They have rudimentary lungs, which allow them to obtain oxygen from the air when in poorly oxygenated waters by swimming quickly to the surface and back to the bottom.
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