Indirect effect of salmon carcasses on growth of a freshwater amphipod, Jesogammarus jesoensis (Gammaridea): An experimental study

The effect of salmon carcasses on the growth of a freshwater amphipod, Jesogammarus jesoensis (Schellenberg) (Gammaridea, Anisogammaridae), was examined experimentally. Growth rate was determined by rearing juvenile amphipods in four food treatments (‘leaves’, ‘salmon’, ‘leaves and salmon’ and ‘leaves with salmon leachate’) for 20 days. Mass loss and oxygen consumption of the leaves were also measured in the three treatments with leaves. The oxygen consumption rate of leaves was lower in the ‘leaves’ treatment than in either the ‘leaves and salmon’ or ‘leaves with salmon leachate’ treatments, indicating that microbial activity on leaves was enhanced by the presence of salmon carcasses. Mass loss of leaves did not differ between the three treatments with leaves. The growth rate of the amphipods did not differ between the ‘leaves’ and ‘salmon’ treatments, or between the ‘leaves and salmon’ and ‘leaves with salmon leachate’ treatments. Growth rates in the two latter treatments were higher than rates in the ‘leaves’ treatment, but not higher than the rates in the ‘salmon’ treatment. Therefore, it appears likely that consuming leaves fertilized with nutrients from salmon carcasses facilitates growth in this amphipod.