IX. Metabolism

The digestive system

Fish physiology
Please try again later. Their kidneys produce dilute urine for excretion. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases. There was a problem with your submission. Gills are tissues which consist of threadlike structures called filaments. Fish eyes are similar to those of terrestrial vertebrates like birds and mammals, but have a more spherical lens.

General features


Gill rakers in these fish are typically fine to prevent the escape across the gills of small food particles. The esophagus, which is lubricated by mucus, leads to the stomach. In carnivorous fish, the stomach is muscular and elastic for holding large prey items, while in omnivorous and planktivorous fishes the stomach, if present at all, is small because a more or less constant stream of small food particles can flow directly into the intestine.

The pylorus is a sphincter that prevents premature movement of the food bolus out of the stomach. Around the pylorus, many fish have out-pocketings called pyloric caeca. The role of pyloric caeca in digestion has been widely speculated upon. Histologically, they are very similar to the intestine.

Around the pyloric caeca or in that same area in fish lacking them is pancreatic tissue. Alex Safian and Danielle Baker A standard bony fish contains a two chambered heart that is located below the gills. Bony fish and sharks are known to be a single circulation species. The Heart What is single circulation? The Countercurrent System First, the blood in the gills flows in the opposite direction to the water passing over them.

When the water has passed over the gills, the blood is "hungry" for the oxygen that is there. The blood then becomes rich in oxygen. Single circulation is when the blood passes through the heart once every time it circulates. Gas Exchange Gas exchange is when diffusion takes place, in the gills, only if oxygen is more concentrated in the water than in the blood.

However, once the oxygen is diffused into the gills, the water surrounding the fish is depleted, and gas exchange loses its efficiency. This is then solved by a countercurrent system. The Circulatory System When the fish is in a stable state, deoxygenated blood flows into the fisrt chamber of the heart from the body. The blood is then pumped into the second chamber of the heart, and is brought to the gills where gas exchange takes place.

Once the oxygenated blood is carried back to the body by its arteries, it is then branched out into thin-walled capillaries that allow nutrients flow to a cell.

In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.

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Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. The digestive system The digestive system , in a functional sense, starts at the mouth , with the teeth used to capture prey or collect plant foods. Previous page The skin. Page 6 of 9. Next page The respiratory system. Learn More in these related Britannica articles: Of the approximately species of freshwater fish of the United States, Canada, and Mexico, about 40 have become extinct in the past….

The earliest known vertebrates were jawless fishes of the class Agnatha, and their only living representatives are the cyclostomes—the lampreys and the hagfishes. The modern agnathans retain much of the general organization of the ancestral vertebrates, and, therefore, much of their musculature is…. Similar to other vertebrates, fish have discrete taste and smell systems; however, since they live in water, the taste system is not confined to the oral cavity. For example, taste buds occur on the lips, the flanks, and the caudal tail fins of some….

The cyclostomes and the elasmobranchs e. There are, nevertheless, two possible ways by which some of these cartilaginous fishes, especially the sharks, react to sounds in the water: Generally meats consist of about 20 percent protein, 20 percent fat, and 60 percent water.

More About Fish 68 references found in Britannica articles Assorted References conservation and extinction issues In conservation: Freshwater fish In conservation: In the oceans In conservation: Culture and religion anatomy and physiology bioluminescence In bioluminescence: The role of bioluminescence in behaviour body part regeneration In regeneration: Fishes chemoreception In chemoreception:

A. Digestive System