Is reduced body growth of cod exposed to the gill parasite Lernaeocera branchialis a cost of resistance?

Three hundred and sixty-nine Atlantic cod were individually marked and caged for 19 months. During this period each cod was inspected several times for Lernaeocera branchialis (L.). Growth rates in four groups of cod, identified by their infection history, were compared. During the caging 79 % of the cod remained uninfected, 8.5 % were infected, but lost the parasite, 8 % were infected with one parasite, and 4.5 % were infected with more than one parasite. [It is not clear if you are referring to parasites that were there at the beginning or ones which arrived later]The highest rate of increase, both in body mass and body length, was recorded in the group of male fish infected with one parasite throughout the experimental period. Conversely, those males free from infection, showed significantly lower growth rates. The observed differences in growth rates could not be explained by changes in parameters related to reproductive strategies. The alternative explanation for these results is that resistance to L. branchialis was associated with costs in terms of reduced growth rates of body mass and length.