Quite a lot of fish chew their food. The ones that I know of are the carp, cichlids, catfish and loaches. These are all freshwater, and are huge families which include most freshwater fish species. They have teeth on the pharyngeal bones. Some also have teeth in the front of the mouth, such as many catfish species and cichlids.
Although they may survive for a long time out of water in damp conditions, the goldfish and carp never leave the water voluntarily and are not adapted to move on land. Their fins have weak rays which will not support their weight. I am not sure whether they are able to absorb oxygen from the air with their swim bladder in emergencies. They can certainly empty and fill it through the mouth. When a goldfish is stressed it will sometimes expel air from its mouth with a 'popping' sound and sink to the bottom. When the danger is past it will gulp air at the surface to regain buoyancy. Newts and salamanders will empty their lungs, often with a squeak, when disturbed, to escape danger by sinking.
Most aquatic animals, including most fish, produce ammonia as a waste product, excreting it through their gills. Mammals produce urea and excrete it through their kidneys. Urea is far less toxic and so does not need to be immediately excreted and diluted. The goldfish is one of a few species which can change from producing ammonia to urea if the ammonia concentration in the water is becoming dangerous. Any fish species which leaves the water must take this step.
The loaches and catfish, which are related to the carp family, often leave the water. Most of them can breathe air, by intestinal respiration or modified gills. Some, such as the weather loach, are long and thin, and move like snakes on land, without using their fins much. Others 'walk' on strong fin rays. Plecos and Corydoras do not leave the water often, but they can stand on their fins, and I have seen small plecos 'walking' underwater on a sandy substrate, using their strong and spiny fins with a movement like a salamander.
Many amphibious species, such as Weather Loaches, Walking Catfish and Climbing Perch will leave the water in wet weather to find new ponds with food and potential mates. This is often triggered by low barometric pressure (which predicts rain), and captive ones may escape their tank. If they are able to, Walking Catfish will climb into a neighbouring tank or pond and eat the occupants.
|
