Is reduced body growth of cod uninfected with the gill parasite L. branchialis a cost of resistance?

Six hundred Atlantic cod were individually marked and caged for 19 months. During this period each cod was inspected for L. branchialis at several points in time. Growth rates in four groups of cod, identified by their infective history, were compared. During the caging 78.4 % of the cod remained uninfected, 8.4 % were infected, but lost the parasite, 7.9 % were infected with one parasite, and 4.3 % were infected with two or more parasites. The highest rate of increase both in body mass and body length, was recorded in the group of fish infected with one parasite throughout the experimental period. Contrary, the fish which were free from infection, showed the lowest rate of increase in body mass, and the second lowest increase in body length.The observed differences in growth rates could not be explained bychanges in parameters related to life history strategies. Thealternative explanation to these results, is that resistance to L.branchialis was associated with costs in terms of reduced growthrates of body mass and length.