Correlation of parasites with growth of yellow perch.

The possible influence of parasites on the short-term and long-term growth and condition of yellow perch Perca flavescens was examined by investigating correlations between parasite abundance and specific growth variables. The following parasites were enumerated in age-1 yellow perch collected from Lake St. Pierre in June 2008: Apophallus brevis, Diplostomum spp., Ichthyocotylurus spp., Tylodelphys scheuringi, Phyllodistomum superbum, and Raphidascaris acus. Short-term growth was estimated using RNA/DNA ratios and long-term growth via the total length and condition as measured by the Fulton index. No correlation was found between parasite abundance and short-term growth, but a negative influence of combined infections of T. scheuringi and P. superbum on long-term growth was detected. In addition, the abundance of Ichthyocotylurus spp. was positively correlated with the condition of the yellow perch. Together these results suggest that limited or subtle pathogenic effects in juvenile fish are not discernable in recent growth but only in long-term growth indices. Furthermore, in future studies examination of parasite effects on fish growth should account for multiple infections.