Osmotic Regulation in the Brackish Water Teleost, Blennius Pholis

Abstract

1. The sodium effluxes between the blood and the medium have been studied in Blennius pholis in 10, 40 and 100% s.w. and in transfer from 40 to 100% s.w. under equilibrium conditions with the isotope 24Na. In addition the sodium influxes have been studied in 40 and 100 % s.w. in a similar manner. 2. The total flux in 100% s.w. has been found to be 100 mM. Na/l. blood/hr., and in 40 and 10% s.w. it has been found to be 20 mM. Na/l. blood/hr. 3. The results are interpreted as showing that the presence or absence of exchange diffusion does not alter the estimation of the active sodium efflux across the gills in 100% s.w. 4. The efflux experiments showed that the animal had a rapid adaptive ability to osmo-regulate upon transference from 40 to 100% s.w. 5. The electric potential differences between the blood and external medium have been measured in animals adapted to 10, 40, 100 and 150% s.w. and the blood serum concentrations of sodium and chloride ions have been measured in these media. 6. The mean potential differences ± standard deviation in 10, 40, 100 and 150% s.w. have been found to be -3±4.5 mV., +23±4 mV., +23 ±3 mV. and +29.5±5 mV. respectively (external medium taken as reference). 7. The results are interpreted as showing that there is active outward excretion of chloride ions in animals adapted to 150, 100 and 40% s.w. and active inward absorption of chloride ions in 10% s.w. and of sodium ions in animals adapted to 40 and 10% s.w. 8. The drinking rate in 100% s.w. has been calculated to be 27 mM. Na/kg. fish /hr. or 6% body weight/hr.