The aim of this study was to evaluate expression of the stress-related genes heat shock proteins 90 and 70 (Hsp90 and Hsp70) and ferritin in Acartia tonsa in order to explore whether epibiont infestationleads to detectable changes in expression of stress-related genesunder laboratory conditions. The overall methodology was firsttested by examining a more straightforward parameter, namely the effect of rapid temperature changes (heat shocks) on copepod stressgene expression and the dependence of heat shock on salinity.