Epidemiological Study of Parasites of the Edible Scallop <i>Aequipecten tehuelchus</i> in Patagonia, Southwest Atlantic Ocean

This study assesses the health status of the edible Tehuelche scallop, Aequipecten tehuelchus, reporting the epidemiological results of the parasites and their infection levels by histopathological analysis and transmission electron microscopy. Environmental factors (site: West and East domains of the San José gulf, seawater temperature) and host traits (size, physiological condition index, gonad development stages) associated with parasite load (prevalence, mean intensity, parasite abundance and total parasite abundance) were tested with generalised linear models (GLMs). Histopathological results revealed Rickettsia-like organisms (RLOs), several protozoans (Trichodina sp., Nematopsis sp. and APXSc apicomplexans) and metazoans (turbellarians and Tumidotheres maculatus pea crabs) as well as inflammatory lesions in form of granulomas and hemocytic infiltration. The prevalence of the parasitofauna did not vary significantly between gulf domains, except the apicomplexan APXSc that was significantly most prevalent in scallops from the East Domain. However, the mean intensity of infection seemed to be determined by the gulf domains, which present distinct hydrographic regimes, where RLO's, Trichodina sp. and T. maculatus were significantly more intense in scallops from the West, opposite with Nematopsis sp. infection. Total parasite abundance was influenced by seasonal variations, it was negatively correlated with warmer temperatures. The physiological condition index of A. tehuelchus seemed not to be affected by the presence or abundance of any of the parasites. Nevertheless, the apicomplexan APXSc would represent a significant risk to the health of A. tehuelchus due to the pathological conditions, and surveillance of this parasite is needed for a sustainable A. tehuelchus fishery.