Effect of a single Lernaeocera branchialis (Copepoda) on growth of Atlantic cod.

A study was conducted to determine the influence of controlled water temperature on growth rate of Atlantic cod (Gadus morhua) after infection with a single, blood-feeding copepod, Lernaeocera branchialis. Initially, uninfected and infected fish were held in ambient seawater (0-10 C) in a raceway and fed to satiation from October to March. In a second trial simulating the water temperature at which cod live in winter (2-3 C), 2 groups of fish were kept in tanks through which sea water flowed, and they were fed to satiation from February through July. Infected cod held at the ambient temperature consumed more feed, had comparable weight-gain, and showed lower feed conversion efficiency (%) and k-factor than did control fish during autumn to early winter, whereas no difference was apparent during the remaining winter period. Also, no striking difference in feed consumed, weight gained, feed conversion efficiency or k-factor were apparent when the 2 groups of cod were held in heated sea water during winter to early summer. These results suggest that adult cod infected with 1 L. branchialis compensate for the infection in autumn rather than during winter by consuming more fed.