Drinking behaviour in sea water and fresh water teleosts,the role of the renin-angiotensin system

Basal drinking rate and responses to administered angiotensin were examined in 12 species of fish. The responses of representative euryhaline, stenohaline marine and fresh water species to pharmacological manipulation of endogenous renin-angiotensin system (RAS) activity were also investigated.Basal drinking rates were consistently low in stenohaline and euryhaline fresh water fish, and all species examined showed an increased imbibition in response to administered angiotensin. Marine fish drank large volumes of water, rates varying considerably between species, with euryhaline species exhibiting lower rates than stenohaline groups. The extremely high drinking rates observed in the sea scorpion were associated with a high plasma osmolality. With the exception of the sea scorpion, all other species examined in sea water showed a further rise in drinking in response to exogenous angiotensin.Although the freshwater stenohaline carp showed a dipsogenic response to angiotensin, it was apparently unable to evoke this response when fish were acclimated to brackish water. The high drinking rates of both euryhaline and stenohaline fish held in sea water appeared dependent upon an activated endogenous RAS, and were lowered following inhibition of Al to All conversion by Captopril. Drinking was further stimulated in these marine species following stimulation of endogenous RAS activity by the administration of the hypotensive agent Papaverine. The study endorses a role for the RAS in the control of adaptive drinking in euryhaline and stenohaline marine teleosts.