Endocrine Control of Hydromineral Balance in Teleosts

Hydromineral balance in teleosts is reviewed in an effort to define common elements, as well as inter- and intra-species variation in its endocrine control. Processes at the gill, gut, kidney, and urinary bladder are compared. The difficulty in deriving functional generalities is discussed; the stimulation of both sodium influx and efflux by cortisol, the ingestion of equal amounts of water by some fishes in either fresh or sea water, and the equal glomerular filtration rates in both hypotonic and hypertonic environments for other fish confound such efforts at generalization. An attempt is made to explain these inconsistencies through an examination of variation in hormonal balances and effector organ responses. Evidence for Na+/K+-ATPase involvement at the gill, gut, kidney, and urinary bladder is summarized. Patterns in cortisol and prolactin availability as a function of synthesis, storage, and secretion are considered. A rather consistent antagonism of cortisol and prolactin in sodium movement and water permeability at several teleost effector organs is substantiated.