Effects of biodensity on the growth, stress physiology, and welfare of Arctic charr (Salvelinus alpinus) in freshwater

Biodensity is a major factor affecting the production and welfare of farmed fishes. Arctic charr (Salvelinus alpinus) (average mass 176.9 +/- 3.9 g) were held at biodensities of 30, 60, 90, 120, and 150 kg/m(3) (4 replicates per treatment) during a 91 day study which examined key growth, stress physiology, and welfare parameters. During experimentation fish were fed to near satiety, and a random subsample of 20 fish (5 per replicate tank) were collected from each treatment every 21 days. Biodensity was found to have no significant effect on mortality rates or physical fin damage. Growth rates were lower in charr reared at the highest biodensities (120, and 150 kg/m(3)), while feed efficiency was negatively affected at both the highest (120, and 150 kg/m(3)) and lowest (30 kg/m(3)) biodensities. Plasma cortisol indicated that Arctic charr are more stressed at lower biodensities, but was not correlated with growth or feed efficiency measures. The results support an optimal biodensity range for charr culture between 60 and 90 kg/m(3) to optimize production and welfare.