Intestinal nutrient transport in coho salmon (Oncorhynchus kisutch) and the effects of development, starvation, and seawater adaptation

Intestinal nutrient transport in yearling coho salmon was characterized and adaptive changes in nutrient transport were described in relation to development, starvation, and environmental salinity. Salmon intestine exhibits a small transepithelial potential difference (TEP: -1.4 to 2.0 mV, mucosa ground) and low resistance (41 to 181 ohms·cm²) that varied with the region along the intestine, with starvation, and with environmental salinity. Addition of glucose or proline to the mucosal side of intestine caused a rapid increase in short-circuit current. Isotopic mucosalto-serosal net fluxes of glucose and proline were achieved across salmon intestine in the absence of transepithelial chemical or electrical gradients. A sleeve technique for measuring proline influx (Karasov and Diamond 1983a) was validated for use in salmon intestine. Comparison of total proline influx in different intestinal regions showed the following order (from highest to lowest rates): pyloric caeca ≫ anterior intestine > posterior intestine. Total proline influx was highest in April during the parr-smolt transformation. The kinetics of Na^α-dependent proline influx were altered by starvation and seawater adaptation. Starved fish exhibited a lower K_t but similar J_max in anterior intestine compared with values in fed fish. The effect of seawater adaptation on the kinetics of proline influx varied with the timing of entry into seawater, with length of seawater residence, and with season. Growth-inhibited SW stunts showed a reduced J_max of proline influx compared with that of normal SW smolts.