Functional models for growth and food consumption of Atlantic salmon parr, Salmo salar, from a Norwegian river

1. The chief objectives were to analyse and model experimental data for maximum growth and food consumption of Atlantic salmon parr (Salmo salar) collected from a cold glacier fed river in western Norway. The growth and feeding models were also applied to groups of Atlantic salmon growing and feeding at rates below the maximum. The growth models were validated by comparing their predictions with observed growth in the river supplying the experimental fish. 2. Two different models were fitted, one originally developed for British salmon and the other based on a model for bacterial growth. Both gave estimates for optimum temperature for growth at 18-19 degreesC, somewhat higher than for Atlantic salmon from Britain. Higher optimal temperature for growth in salmon from a cold Norwegian river than from British rivers does not concur with predictions from the thermal adaptation hypothesis. 3. Model parameter estimates differed among growth groups in that the lower critical temperature for growth increased from fast to slow growing individuals. In contrast to findings for brown trout (Salmo trutta), the optimum temperature for growth did not decrease with decreasing levels of food consumption. 4. A new and simple model showed that food consumption (expressed in energy terms) peaked at 19.5-19.8 degreesC, which is similar to the optimal temperature for growth. Feeding began at a temperature 1.5 degreesC below the lower temperature for growth and ended about 1 degreesC above the maximum temperature for growth. Model parameter estimates for consumption differed among growth groups in a manner similar to the growth models. Maximum consumption was lower for Atlantic salmon than for brown trout, except at temperatures above 18 degreesC. 5. By combining the growth and food consumption models, growth efficiency was estimated and reached a maximum at about 14 degreesC for fast growing individuals, increasing to nearly 17 degreesC for slow growing ones, although it was lower overall for the latter group. Efficiency also declined with increasing fish size. Growth efficiency was generally higher for Atlantic salmon than for brown trout, particularly at high temperature.