Does Diplostomum sp. infection stimulate growth in juvenile Arctic charr?

The effect of parasitism on fish growth is usually expected to be negative. Here, we report a possibly positive association between fish growth and parasite exposure. We measured specific growth rates (SGR) and standard metabolic rates (SMR) of juvenile Arctic charr Salvelinus alpinus before and 12 to 40 days after exposure to 53 to 89 Diplostomum sp,. cercariae fish super(-1). SGR correlated positively with the number of Diplostomum sp. cercariae to which the fish were exposed, whereas the number of cercariae located in the fish eye lens was not associated with SGR. There was no evidence of fish with high SMR and/or initial fresh mass being more susceptible to the parasites. Parasite challenge had no effect on the temporal consistency of SMR. These results indicated that exposure to Diplostomum sp. affected host SGR but not SMR. This study emphasises that traits of host-parasite relationships are not straightforward but rather unique for each host-parasite combination.