Understanding feeding and digestion in fish.

Also of Interest

Digestive System in Fishes (With Diagram)
The function of the se cells is unknown. At the anterior end of the midgut a number of blind ending tubes may be present - these are the pyloric caecae. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Caecae are present in salmonids but absent from cyprinid species. The Puffer fish has a stomach that can be inflated with air or water in order to scare off enemies. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten.


IX. Metabolism

For those fish species with a stomach, two areas can be identified - a cardiac area anteriorly i. In stomachless fish, the wall of the anterior midgut secretes digestive enzymes but not hydrochloric acid.

In carnivorous fish the intestine is relatively short whilst that of herbivorous fish, which tend to lack a stomach, is long and much folded to increase the contact and absorption time. At the anterior end of the midgut a number of blind ending tubes may be present - these are the pyloric caecae.

They appear not to be associated with any particular type of diet and the number, if they are present, varies from species to species. Several functions have been attributed to them including increasing the surface area of the intestine for food absorption, specific site of carbohydrates and fat absorption and adding to the digestive functions of the stomach.

Caecae are present in salmonids but absent from cyprinid species. An important source of digestive enzymes is the pancreas. This organ is adjacent to the stomach and can be a discrete or diffuse organ depending on species. In salmonids the pancreas is a diffuse collection of cells interwoven amongst the pyloric caecae. Enzymes are produced by the pancreas only in the presence of food and are involved in the breakdown of all nutrients.

Both the liver and the gall bladder play an important role in digestion. The liver both assimilates the products of digestion into usable forms and aids the digestive process through the production of bile which is stored in the gall bladder.

The size and fullness of the gall bladder is indicative of feeding status in fish. A large, distended bladder indicates that the fish has not eaten for some time whilst an empty flaccid bladder indicates that the fish has recently eaten a meal. Bile is excreted from the bladder to the intestine via the bile duct. 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. Often, popular bottom-dwelling fishes such as loricariids and Corydoras catfish are expected to survive on the leftovers from the other fish. This is not an acceptable practice, and these fish should receive targeted feeding. Another consideration is quantity of feed fed. Various types of feeds have dramatically different weights.

For example, flaked feeds tend to be much lighter than pelleted feeds. Pelleted feeds come in different sizes and can be floating or sinking. In predatory carnivorous fishes, the mouth is usually large for engulfing prey whole, or in large chunks, and teeth are present on the jaws e. Gill rakers are short in carnivorous fish and pharyngeal teeth are short and pointed for moving prey down the throat.

In omnivorous and planktivorous fishes, the mouth is smaller and is usually devoid of teeth except for pharyngeal teeth that may be blunt and flat molariform for grinding or sharp and long for shredding. 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 digestive system