A comparison of body condition of the yellowstriped butterfish Labracoglossa argenteiventris in relation to parasitism by the cymothoid isopod Ceratothoa arimae

Abstract

Isopods of the genus Ceratothoa (Cymothoidae) are one of the largest invertebrates parasitic on a variety of fishes, which include commercially important species. Nevertheless, the parasitic effects on fish body condition have been studied only in a few Ceratothoa species, particularly those living in the Mediterranean and Australian waters. Findings from these previous studies suggest the hypothesis that effects of parasitism by Ceratothoa species are benign on native host condition in the wild. In this study, to test this hypothesis on another Ceratothoa–fish relationship in different region, we examined the effects of Ceratothoa arimae on the body condition of the yellowstriped butterfish, Labracoglossa argenteiventris, a commercial fish important to local fisheries particularly in the remote islands of Tokyo, Japan. Ceratothoa arimae was found in 8 out of 23 fish examined (prevalence: 34.8%). Although infected and uninfected fish were similar in standard length, the body condition index (relative weight) of infected fish was significantly lower than that of uninfected fish. The observed weight of infected fish was an average of 89.2% of the expected weight. These results are inconsistent with the hypothesis and suggest that the potential effects of Ceratothoa parasites need to be considered carefully in fishery management plan of host fish.