A demersal fish is a fish that feeds on or near the bottom of the ocean or a deep lake in the demersal zone. Demersal fish are also known as bottom feeders, groundfish or benthic fish, and may be contrasted with pelagic fish. Compared to pelagic fish, they contain little oil (one to four percent).
Examples
Some examples of demersal fish include cod, haddock, whiting, halibut, perch, snapper, eel, grouper, bream, bass, orange roughy, flounder, plaice, demersal shark and some species of catfish.
Behaviour
Demersal fish output in 2005
Bottom feeders are not necessarily detrivores, although there are many that are. Some bottom feeders graze along the bottom, feeding on plant material. Other bottom feeders may feed on other bottom feeders, and thus are carnivores.
Some demersal fish are capable of burying themselves, such as flatfish or stingray. As with other bottom feeders, a mechanism to deal with substrate is often necessary. With demersal fish the sand is usually pumped out of the mouth through the gill slit. Most demersal fish exhibit a flat ventral region so as to more easily rest their body on the substrate. The exception may be the flatfish, which are laterally depressed but lie on their sides. Also, many exhibit what is termed an "inferior" mouth, which means that the mouth is pointed downwards; this is beneficial as their food is often going to be below them in the substrate. Those bottom feeders with upward-pointing mouths, such as stargazers, tend to seize swimming prey.
Regulations
Saltwater groundfish harvesting is subject to numerous federal regulations in the United States, principally 50 CFR 679, dealing with fishing in Alaskan waters.
Freshwater groundfish harvesting is not subject to federal regulation per se (certain species may be subject to other rules), perhaps because there are fewer true groundfish species that live in fresh water.
Benthopelagic fish
In addition, some species are benthopelagic, that is, they live near the bottom as well as in midwaters or near the surface, feeding on benthic as well as free swimming organisms. Some examples are Halosauridae, Macrouridae, Moridae, Pandalus borealis and Etmopterus.
See also
Notes
References
External links
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