Cloacal and salt-gland ion excretion in the seagull, Larus glaucescens, acclimated to increasing concentrations of sea water

Abstract

1. 1. Gaucous-winged gulss, Laurs glaucescens, were acclimated sequentially to fresh water, 1 3 , 2 3 and 3 3 sea water for periods of 1–2 months. Sodium, K and Cl concentrations in the plasma (no K values), cloacal fluid and NaCl-induced salt-gland secretion were determined (spontaneous salt-gland secretion was analyzed when observed), and body weight and hematocrit were recorded weekly. 2. 2. Plasma Na concentration was lower in fresh-water birds than in birds acclimated to 1 3 sea water. Increased salinity of the drinking water had no further effect. Chloride concentration was the same in birds on all drinking water regimes. 3. 3. In only 12 of 331 cloanal fluid samples was Na hypertonic to plasma; in only 35 of 336 samples was Cl hypertonic. 4. 4. Cloanal retention of fluid lowered its Na and Cl but increased (or did not change) K concentration. 5. 5. In NaCl-induced salt-gland secretion Na and Cl concentration were higher in 1 3 sea water than in fresh-water-acclimated gulls, but further increase in drinking water concentration did not enhance this effect; K concentration of sea-water-adapted birds was twice that of fresh-water birds. The Na : K ratio in fresh-water birds was 24 : 1, 12 : 1 in sea-water birds. 6. 6. Hypertonic spontaneous salt-gland secretion was observed in gulls drinking fresh water to 2 3 sea water. Ion concentration increased as drinking-water concentration increased, but Na and Cl were not always of similar concentration as in NaCl-induced secretion. 7. 7. Body weight and hematocrit were lower in gulls adapted to sea water than in fresh-water birds. 8. 8. These data further suggest that a major portion of ingested. Na and K may be extrarenally excreted even in the absence of imposed osmotic stress and that the cation concentration in the salt-gland secretion is dependent upon the magnitude of the osmotic stress.