Changes in intestinal absorption and renal excretion of water during adaptation to sea-water in the Japanese eel

Abstract

The rate of sea-water ingestion in Japanese cultured eels, Anguilla japonica, adapted to sea-water for one week, was 89±9.5 ml/kg/day; approximately 75% of the ingested water was absorbed by the intestine. Similar rates of ingestion and absorption of water were also found with sea-water-adapted rainbow trout, Salmo gairdnerii, and two species of marine teleosts, Stephanolepis cirrhifer and Goniistius zonatus. When cultured eels were transferred from freshwater to sea-water the amount of ingested and absorbed water inoreased gradually to a maximum on the 5th day and then decreased to a constant level. The urine flow and glomerular filtration rate were found to be high in freshwater cultured eels, and both reduced markedly within 6 h after transferring the eel to sea-water. The reabsorption of water by the renal tubules was very small in both the freshwater and sea-water-adapted (6 h) eels. On the other hand, in the eels adapted to sea-water for 10 days the rate of urine flow was also very slight but the glomerular filtration rate recovered to that of the freshwater eels. Thus, water reabsorption by the tubules increased to a large degree. The results seem to indicate the existence of two distinct phases in the renal function during sea-water adaptation of cultured eels.