Prevalence and effects of the cymothoid isopod (Ceratothoa oestroides, Risso 1816) on cultured meagre (Argyrosomus regius, Asso 1801) in the Eastern Adriatic Sea

Meagre (Argirosomus regius) is a relatively new farmed fish species in Croatian mariculture. This study is the first attempt to determine the prevalence of cymothoid isopod parasite Ceratothoa oestroides and its effects on cultured meagre in the Mediterranean area. When analysing growth of meagre at two sites in the central part of the Eastern Adriatic Sea, the greatest difference in total fish length was recorded in March 2016, when fish with parasites were 33% smaller than fish without parasites (24.47 +/- 3.29 vs. 16.28 +/- 1.01cm; p < .001). The largest difference in mass was also recorded during sampling in March, when parasitized fish was 74% lighter than the unparasitized fish (171.75 +/- 72.96 vs. 44.77 +/- 6.57g; p < .001). The presence of the cymothoid isopod in the buccal cavity was observed, and caused fish deformation throughout the entire duration of the study. Also, female parasites with pulli II in marsupium were found. Based on the determined prevalence and effects on production and health status, monitoring of the interaction between C.oestroides and meagre should be considered in future management plans for cultivation of this promising species for Mediterranean aquaculture.