Oldfield_Saltwater_Cichlids_2004 - Saltwater cichlids....

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Accessible at: (http://deepblue.lib.umich.edu/index.jsp) © Ronald G. Oldfield 2004 1 Saltwater cichlids. Knowledge of salinity tolerance and preference may allow new species combinations and improved husbandry in aquaria. Ronald G. Oldfield University of Michigan, Department of Ecology and Evolutionary Biology Museum of Zoology, 1109 Geddes Ave., Ann Arbor, MI 48109 U.S.A. E-mail: roldfiel@umich.edu A version of this article appeared as: Oldfield, R.G. 2004. Salty cichlids. Knowledge of salinity tolerance and preference may allow new species combinations and improved husbandry in aquaria. Freshwater and Marine Aquarium . 27(8): 98-104. Maybe you have been in your local fish shop and have seen the occasional molly swimming gleefully in a saltwater tank. You stop, puzzled. Upon inquiring, you learn that mollies often live in coastal estuary and lagoon habitats, capitalizing on that middle ground between land and sea. The store representative tells you that it is not that hard to convert such a fish from freshwater to full strength seawater. You find it interesting, but move on. Most people that invest in marine aquaria yearn for the brilliant colors typical of reef dwelling species, or robust predators that would make short work of a molly. However, would you be surprised to know that several cichlids are also tolerant of full strength seawater? Knowledge of salinity tolerance could open doors to housing new combinations of species, and knowledge of salinity preference could bring an aquarist one step closer to providing ideal husbandry. One of the primary characteristics of life is homeostasis, the maintenance of a constant internal environment in the face of changing external factors. Teleost fishes maintain constant internal concentrations of ions and water that are different than that of the surrounding medium. They accomplish this through the functions of the gills, kidneys, skin, gut, and urinary bladder. A fish in a hypo-osmotic medium like seawater maintains a higher concentration of water and lower concentrations of ions than in the surrounding fluid. This creates a concentration gradient, and results in osmosis: transport of water out of the fish’s body. The fish responds by drinking more than it would in an isotonic solution. The swallowed water is absorbed by the gut along with dissolved ions like sodium (Na + ), potassium (K + ), and chloride (Cl - ). Surplus ions are secreted out of the body by chloride cells embedded in the gill epithelia. Saltwater adapted fish have more mitochondria and extensive invaginations in the chloride cells that aid them in secreting excess ions. Freshwater is hyper-osmotic to a fish and water diffuses in through the gills. This causes the fish to excrete large amounts of dilute urine and take up needed ions like Na + and Cl - through the gills (Karnaky 1998). Cichlids have long been known to be euryhaline, or
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Oldfield_Saltwater_Cichlids_2004 - Saltwater cichlids....

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