Atlantic salmon in duoculture with Arctic charr: decreased aggression enhances growth and stocking density potential

Abstract

Reduced aggression for Atlantic salmon in duoculture with Arctic charr, compared to monoculture, was previously reported. It was then not clarified whether the reduction of aggression was a result of reduced salmon stocking density itself, or alternatively, if the physical presence of Arctic charr reduced the probability for visual and physical contact between salmon additionally (termed shading). To test these hypotheses, Atlantic salmon and Arctic charr were reared in mono- and duoculture under two densities; 0.6 and 1.2 individuals 1 −1. Variations in Atlantic salmon length, weight and condition factor were significantly affected by culture type and salmon density, but not by total fish density. Culture type and charr density did not significantly affect charr size parameters, except for variation in condition factor. For a given salmon density, addition of charr reduced the aggression received by each salmon and increased mean salmon size and growth rate significantly. Duoculture improved growth rate in salmon due to shading between conspecifics. A practical application of the results could imply increased total stocking density potential of salmonids.