Internal Anatomy

The major parts of a fish's skeleton, shown in Figure 39-11, are the skull, spinal column, pectoral girdle, pelvic girdle, and ribs. The spinal column is made up of many bones, called vertebrae, with cartilage pads between each. The spinal column also partly encloses and protects the spinal cord. The pectoral girdle supports the pectoral fins, and the pelvic girdle supports the pelvic fins. In a human skeleton, the pectoral girdle is the shoulder and its supporting bones, and the pelvic girdle is the hips. A fish's skull is composed of a large number of bones (far more than are in the human skull) and is capable of a wide range of movements. Note the pectoral fin rays and pelvic fin rays that are key characteristics of ray-finned fishes.

Digestive System

Bony fishes have diverse diets but commonly are carnivores. The jaws of predatory fishes are lined with many sharp teeth that point inward to keep prey from escaping. Strong muscles operate the jaws, which are hinged to allow the mouth to open wide.

Figure 39-12 on the next page shows the internal anatomy of a bony fish. Food passes from the mouth into the pharynx, or throat cavity, and then moves through the esophagus to the stomach. The stomach secretes acid and digestive enzymes that begin to break down food. From the stomach, food passes into the intestine, where digestion is completed and nutrients are absorbed.

The liver, located near the stomach, secretes bile, which helps break down fats. The gallbladder stores bile and releases it into the intestine. The pancreas, also located near the stomach, releases digestive enzymes into the intestine. The lining of the intestine is covered with fingerlike extensions called villi that increase the surface area for absorption of digested foods. Undigested material is then eliminated through the anus.

figure 39-11

The skeleton of Perca flavescens is similar to that of other bony fishes. The general structure of the vertebrae, rib cage, and fins is found in many fishes.

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www.scilinks.org Topic: Anatomy of a

Bony Fish Keyword: HM60065

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www.scilinks.org Topic: Anatomy of a

Bony Fish Keyword: HM60065

Maintained by the iiiivc National Science ■ V'O. Teachen Association

What Bony Fish Fins Called

figure 39-12

The internal anatomy of a bony fish, such as this perch, is a model for the arrangement of organs in all vertebrate descendants of fish. Food passes first from the mouth through the esophagus, then to the stomach and intestines. Finally, undigested waste is eliminated through the anus. Digestion of protein occurs in the stomach, and absorption of nutrients occurs in the intestine.

figure 39-12

The internal anatomy of a bony fish, such as this perch, is a model for the arrangement of organs in all vertebrate descendants of fish. Food passes first from the mouth through the esophagus, then to the stomach and intestines. Finally, undigested waste is eliminated through the anus. Digestion of protein occurs in the stomach, and absorption of nutrients occurs in the intestine.

figure 39-13

A fish's heart is a series of two chambers that act in sequence to move blood through the body, transporting oxygen to the cells and wastes to organs for elimination. Note the thickness of the muscle in the ventricle.

Circulatory System

The circulatory system of a fish delivers oxygen and nutrients to the cells of the body. It also transports wastes produced by metabolism—carbon dioxide and ammonia—to the gills and kidneys for elimination. The circulatory system consists of a heart, blood vessels, and blood. The heart pumps blood through arteries to small, thin-walled vessels, called capillaries, in the gills. There the blood picks up oxygen and releases carbon dioxide. From the gills, the blood then travels to the body tissues, where nutrients and wastes are exchanged. The blood returns to the heart through veins.

The heart of a bony fish has two chambers in a row, as you can see in Figure 39-13. Deoxygenated blood from the body empties into a collecting chamber called the sinus venosus. Next, blood moves into the larger atrium. Contraction of the atrium speeds up the blood and drives it into the muscular ventricle, the main pumping chamber of the heart. Contraction of the ventricle provides most of the force that drives the blood through the circulatory system. The conus arteriosus is a thickened, muscular part of the main artery leaving the heart. It has an elastic wall and usually contains valves to prevent blood from flowing back into the ventricle. The conus arteriosus smooths the flow of blood from the heart to the gills.

Salt Pumped Across Gills

To the gills

To the gills

Water flow

Respiratory and Excretory Systems

The large surface area of a fish's gills allows for rapid gas exchange. Gills are supported by four sets of curved bones on each side of the fish's head. Each gill has a double row of thin projections, called gill filaments. In most bony fishes, water is taken into the mouth and pumped over the gills, where it flows across the gill filaments before exiting behind the operculum. As you can see in Figure 39-14, water flows across the gill filaments in a direction opposite to blood flow. This arrangement is known as countercurrent flow. Counter-current flow causes more oxygen to diffuse into the blood than would be possible if blood and water flowed in the same direction.

A fish's kidneys filter dissolved chemical wastes from the blood. The resulting solution, called urine, contains ammonia, ions such as sodium and chloride, and water. Urine is carried from the kidneys through a system of ducts to the urinary bladder, where it is stored and later expelled. By varying the amount of water and salts in the urine, the kidneys help regulate the water and ion balance in fresh and saltwater fishes.

As blood flows through the gill filaments, ammonia generated by metabolism diffuses from the blood into the water passing over the gills and is removed from the body. The gills also regulate the concentration of ions in the body. Recall that saltwater fishes have lower ion concentrations than sea water has. Therefore, they lose water through osmosis and gain ions, such as sodium and chloride ions. Saltwater fishes make up for this water loss by excreting small amounts of concentrated urine and by drinking sea water, but this increases their internal concentration of sodium and chloride ions. Both kinds of ions are actively transported out through the gills. Freshwater fishes tend to gain water and lose ions. They respond by producing large amounts of dilute urine and actively transporting sodium and chloride ions in through the gills.

Swim Bladder

Most bony fishes have a swim bladder. This thin-walled sac in the abdominal cavity contains a mixture of oxygen, carbon dioxide, and nitrogen obtained from the bloodstream. Fish adjust their overall density by regulating the amount of gas in the swim bladder, enabling them to move up or down in the water.

Swim bladders evolved from balloonlike lungs, which ancestral bony fishes may have used to supplement the oxygen absorbed by the gills. In some fishes, the swim bladder is known to amplify sound by vibrating and transmitting sound to the inner ear.

Water flow

Lable Insdie Fish Gill Filament

Gill filament

Blood flow

Deoxygenated blood figure 39-14

Gill filament

Blood flow

Deoxygenated blood figure 39-14

The gills are located directly behind the head and interior to the operculum. The gill filaments provide the organism with a large surface area, thus enabling gas exchange to occur quickly.

Nervous System

The nervous system of a bony fish includes the brain, spinal cord, nerves, and various sensory organs. The fish brain is illustrated in Figure 39-15. The most anterior part of the brain, the forebrain, contains the olfactory bulbs, which process information on smell. The forebrain also includes the cerebrum, which has areas that integrate information from other parts of the brain. Behind the forebrain lies the midbrain, which is dominated by the optic tectum. The optic tectum receives and processes information from the fish's visual, auditory, and lateral-line systems.

The most posterior division of the brain is the hindbrain, which contains the cerebellum (SER-uh-BEL-uhm) and the medulla oblongata (mi-DUL-uh AHB-lahng-GAHT-uh). The cerebellum helps coordinate muscles, movement, and balance. The medulla oblongata helps control some body functions and acts as a relay station for stimuli from sensory receptors throughout the fish's body. From the medulla oblongata, the spinal cord extends the length of the body and carries nerve impulses to and from the brain.

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Responses

  • walter
    Where is the gall bladder located in a fish?
    11 months ago

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