IX. Metabolism

Protein and fish

Feeding and Digestive Functions in Fishes
High humidity and high temperature result in degradation of the diet, promotion of mold growth and potential mycotoxin production, and rancidity. Feeding a wide variety of feeds is one way to try to meet the nutritional requirements. While they are alternate sources of energy, they are not very necessary for fish growth. Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods gill rakers anchored by one end to the gill bars. The liver is present in all fishes. At the basic level, it can at least be determined whether the fish is carnivorous, omnivorous, or herbivorous. This is very difficult to ascertain, unless you culture your own live food.

ADDITIONAL MEDIA

Digestive System in Fishes (With Diagram)

Hepatic lipidosis is a common problem seen in captive fishes and can occur for multiple reasons. Examples include starvation, a high percentage of carbohydrates in the diet, a high amount of lipids, and rancidity.

Fish require ascorbic acid, delivered in the feed. Most foodstuffs for fish should be supplemented with a stabilized form of ascorbic acid. Severely affected fish exhibit extreme scoliosis.

Feeding a wide variety of feeds is one way to try to meet the nutritional requirements. Live feeds can be varied with diverse commercially prepared feeds. This practice will also help prevent animals from eating only one type of feed. Fishes that feed at the surface should be fed feeds that float, whereas bottom-dwellers should be fed items that rapidly sink.

The feed should be in particles easily ingested by the fish. Flaked feeds may be too large for a small-mouthed fish to easily ingest. Such feeds can be crushed to enable easy ingestion. In contrast, feeding flaked feed to a large fish like an oscar or other cichlid will result in a messy tank, because larger fish cannot easily ingest enough flaked feed to meet their requirements.

When feeding a mixed population of fishes, as is typical in hobbyist tanks, several types of feed items may be required to meet the needs of the fishes. Around the pyloric caeca or in that same area in fish lacking them is pancreatic tissue. In fish the pancreas is usually diffuse, not a discreet body. As in all vertebrates, the pancreas has two digestive functions. It is the source of: The liver in fish produces bile which is stored in the gall bladder until a bolus passes the stomach, at which time the bile is expelled into the intestine.

Bile contains waste products of liver activity which pass out of the fish in the feces. Bile has a digestive function in that it emulsifies lipids, greatly increasing their absorbtion in the intestine. The liver is key in the anabolism and catabolism of amino acids absorbed during digestion and is also the site of storage of food energy in the form of glycogen. The function of the se cells is unknown. Some species of fish Salmonids have pyloric ceca, which are occasionally confused with parasites.

The se ceca secrete the digestive enzymes required to digest some food. Fish without the pyloric ceca have digestive enzyme production in the liver and pancreas. It is not possible to divide the intestine into large and small intestine.

The liver does not have the typical lobular architecture that is present in mammals. In many species of fish the re are areas of exocrine pancreas hepatopancreas that are present near the small veins of f the hepatic portal vein.

The pancreas is scattered in the mesentery, primarily near the pylorus. Irrespective of their main dietary requirements, the digestive systems of fish are very similar. All have a mouth, oesophagus throat , and areas for the absorption of food components fore and midgut and compaction of indigestible waste material hindgut. In adaptation to diet, the major differences are seen in the structure of the mouth and the teeth, the gill rakers, the pharynx, the stomach if present and in the length of the intestine.

In carnivorous fish or those with a meat-orientated omnivorous diet there is a definite stomach foregut whilst herbivorous or plant-orientated omnivores have no stomach but rely on a much extended midgut area.

These two situations are shown below. Digestive system of a Carnivorous Fish. Digestive system of a Omnivorous Fish. Additionally carnivorous fish have extensions to the upper part of the midgut known as pyloric caecae.

Fatty acids and fish