Differences in the physiological status of Atlantic salmon smolts in threetributaries of the River Teno

Physiological characteristics of wild Atlantic salmon smelts at the beginni ng of their migration were compared between three tributaries of the River Teno in northernmost Finland. Samples were collected during or just prior t o the peak of smelt migration. Two of the tributaries are not spawning rive rs but juveniles ascend into them from the main stem. The smelts in these t ributaries were significantly larger when compared to those in a spawning t ributary. Though smelts of all the tributaries survived a salt water challe nge test, significant differences were found in the physiological smelting indices of the smelts between the rivers. The energy stares of smelts were significantly smaller in the spawning river than in the two other tributari es. The smelts sampled at the beginning of the main migration showed high c oncentrations of plasma glucose and protein and a low one for chloride ion, all reflecting an early state of smelting. The size differences of the sme lts between the tributaries did not explain the physiological differences o f the smelts, but the physiological status of the smelts was dependent on t he tributary. (C) 1998 Elsevier Science B.V. All rights reserved.