ROLE OF INTESTINE IN SALINITY ADAPTATION OF RAINBOW TROUT SALMO GAIRDNERI

1. 1. Steady-state drinking rates and intestinal absorption of water and electrolytes in vivo were studied by means of indwelling Foley catheters and a volume indicator (polyethylene glycol). 2. 2. Drinking rates of 47, 95 and 129 ml/kg body wt. per day were measured in one-third-, half- and full-strength sea water and 66, 78 and 80 per cent of these loads were absorbed from the intestine respectively. Fresh-water fish did not drink. 3. 3. Net intestinal salt absorption rates (mM/kg body wt. per day) in one-third, half- and full-strength sea water were: sodium, 4, 19·1 and 56; chloride, 5·5, 23·8 and 67·6; potassium, 0·1, 0·4 and 1·3; calcium, 0·08, 0·11 and 0·43; magnesium, 0·06, 0·37 and 3·13; and sulfate, 0·0, 0·0 and 1·0. Relative absorption rates from ingested loads for sodium and chloride were: sodium, 66, 91 and 99 per cent and chloride, 85, 94 and 98 per cent respectively. 4. 4. In the intestine, ingested media were granually depleted of mono-valent ions and water and enriched in magnesium and sulfate. 5. 5. In plasma-hyperosmotic media, relative absorption of water and monovalent ions were significantly higher (P<0·01). Integumentary water permeability appears to decrease in such media. © 1969.