Prevelance of the parasitic copepod Acanthochondria diastema Kabata, 1965 in wild populations of the southern sand flathead, Platycephalus bassensis

ABSTRACT The spatial and temporal prevalence of the parasitic copepod Acanthochondria diastema was examined in three populations of a key recreational fishery species, the southern sand flathead, Platycephalus bassensis across three geographically separated coastal regions of Tasmania, Australia. The parasitic copepods were observed in the buccal cavity of 21 - 27 % of fish sampled. The weak significant difference in parasite prevalence between regions indicates that there is negligible spatial effect on the prevalence of A. diastema in P. bassensis . Seasonal patterns were region-specific and the effect of location was weak, suggesting high connectivity among P. bassensis populations, likely facilitated by egg/larval dispersal via ocean currents.. Fish length was the strongest predictor of parasite presence, with the probability increasing by approximately 1% for each 1 mm increase in fish length. Fish age contributed significantly in only one region, while there were no sex-specific differences. Although A. diastema was first reported decades ago in P. bassensis , routine encounters have only emerged in recent years, raising concerns that warming waters and fishing pressure are reshaping host–parasite dynamics. These findings highlight the utility of parasite data for understanding exploited fish populations and provide optimism for rebuilding P. bassensis stocks given the limited population structuring in Tasmanian coastal waters.