Changes in intestinal water absorption in coho salmon during short-term seawater adaptation: a developmental study

Abstract

Intestinal water absorption of juvenile coho salmon smolts, pre-smolts, and post-smolts as a function of seawater adaptation was investigated. Net water absorption (Jv) of mid and posterior gut sections in vitro did not change markedly from the freshwater state through 7 days of salt water exposure, although long-term seawater residents had a higher Jv in posterior gut segments, and post-smolts had lower Jv's in both segments than smolts. Rectal fluid [Na +] and pH, and liver [K +], changed in distinctive ways during the first 7 days in seawater, and the changes are compared between developmental stages. Ion analysis of intestinal fluid from different segments of the gastrointestinal tract of seawater-and freshwater-adapted coho indicates that ingested seawater is slightly diluted in the stomach, that 95% or more of the water absorption in seawater-adapted fish occurs in the anterior intestine and pyloric caecae, and that the mid and posterior intestine may be important in water absorption only in the initial stages of seawater adaptation.