Mono- and Duoculture of juvenile Atlantic Salmon (Salmo salar) and Arctic Char (Salvelinus alpinus)

Abstract

In a duoculture experiment with Atlantic salmon parr (Salmo salar) and two Arctic char (Salvelinus alpinus) strains, both species showed increased growth rates compared with monoculture. In duoculture, salmon dispersed more evenly than in monoculture, maintaining positions among the char. Less frequent occurrence of dorsal fin rot was observed in duoculture salmon, probably indicating decreased intraspecific aggression, compared with monoculture salmon. It is suggested that shading and increased dispersion allowed a decrease in intraspecific salmon aggression. Arctic char social hierarchy, indicated by variance of mean inter-renal cell nucleus area, was changed in the presence of salmon, favouring the largest individuals belonging to one of the strains. Different ecological adaptations and size differences can explain the difference in growth gain from duoculture between the char strains. Temperature is suggested as a behavioural regulator in salmon–char duoculture.