Net fluxes of water in the isolated gills of Anguilla dieffenbachii.

Water balance in teleosts, as proposed in the classical theories of osmoregulation originating from the work of Smith (1930), may be summarized as follows. In the marine environment net osmotic water loss from the permeable surfaces of the body, principally the gills, together with the relatively small urinary water loss, is compensated by ingestion of the external medium and the absorption of water from the gut. In the freshwater environment the net osmotic influx of water, again principally at the gills, is balanced by the production of a relatively copious urine. These relationships may be represented in the following manner: