Flow along the gut and intestinal absorption of salt and water in euryhaline teleosts: a theoretical analysis.

Marine teleosts survive in their hyperosmotic environment by drinking the surrounding saline solution. They absorb salt (NaCl) and water through the wall of the gut, and excrete NaCl through the gills. This saves water to make up for the osmotic loss to the surroundings. When the salinity of the surrounding water is changed to a new level, the drinking rate (Maetz & Skadhauge 1968; Potts et al. 1967; Shehadeh & Gordon, 1969), the NaCl turnover of the gills (Maetz & Skadhauge, 1968; Maetz, 1971) and the intestinal transport parameters change (Oide & Utide, 1967; Skadhauge, 1969; Skadhauge, 1974). These regulated processes allow some euryhaline teleosts to adapt to remarkably high salinities (Lotan, 1971). In this paper the role of the intestine in osmo-regulation is subjected to a theoretical analysis by computer simulation of the intestinal transport. In particular we considered the sensitivity of the net intestinal water absorption to the parameters of the system, and the combination of values of these parameters which resulted in maximal water absorption. This allowed comparison with experimental values. Furthermore, using available experimental data from three fish the European eel, the rainbow trout and the cyprinodont Aphanius dispar we tried to predict some consequences which were, or could be, measured experimentally, and to estimate some unmeasured parameters.