All freshwater fishes regulate osmotic pressure and ionic concentrations above their ambient levels. In contrast, all three possible strategies for maintaining salt and water balance are found among fishes inhabiting marine environments. (1) Near osmoconformity/ionoconformity is found in the marine agnathan hagfishes, which are restricted to marine environments and do not regulate main electrolytes and osmotic pressure to any great extent (Morris, 1958). Hagfish do exert limited control over plasma ions by reducing Ca2+ and Mg2+ concentrations to 50% of ambient with a resulting slight hyper-regulation of plasma Na+ (Sardella et al., 2009). However, this control of plasma ionic composition is very minor compared to that displayed by elasmobranchs and teleosts. (2) Osmoconformity with regulation of main ions is seen in marine and some euryhaline elasmobranchs (Evans and Claiborne, 2008; Hazon et al., 2003) and in the lobe-finned coelacanth (Griffith et al., 1974), which, in marine environments, maintain plasma osmolality slightly above that of the surrounding medium but NaCl concentrations at 30%-35% of ambient levels. (3) The most widespread strategy is osmoregulation, found in all teleosts (Evans and Claiborne, 2008; Hwang et al., 2011; Marshall and Grosell, 2006) and lamprey (Evans and Claiborne, 2008; Marshall and Grosell, 2006; Morris, 1958), which regulate Na+ and Cl- concentrations and osmotic pressure at 150 mM and 300 mOsm, respectively, regardless of ion concentrations in their surrounding environment.
|Original language||English (US)|
|Title of host publication||The Physiology of Fishes, Fourth Edition|
|Number of pages||30|
|State||Published - Jan 1 2013|
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)
- Biochemistry, Genetics and Molecular Biology(all)