Health assessment of grey mullet Mugil cephalus based on interrelationship between parasite co-infections and relative condition factor

This study aimed to assess the health status of grey mullet Mugil cephalus by means of relative condition factor under the coexisting parasite groups within seasons. Fish were captured monthly in the Lower Kzlrmak Delta in Samsun, Turkey, from December 2011 to November 2012. A total of five taxonomic groups containing 13 parasite species were constituted: Trichodina (Trichodina puytoraci, T.lepsii), Monogenea (Ligophorus cephali, L.mediterraneus, Gyrodactylus sp., Microcotyle mugilis), Digenea (Ascocotyle (Phagicola) longa, Diplostomum spathaceum, Tylodelphys clavata, Posthodiplostomum sp., Haplosplanchnus pachysomus), Acanthocephala (Neoechinorhynchus agilis) and Copepoda (Ergasilus lizae). Only one mullet was not parasitized and 13.8%, 36.3%, 29.2%, 16.2% and 4.5% were infected by one, two, three, four and five parasite groups respectively. Health assessment of mullets was performed by means of relative condition factor based on weight-length relationship estimated by robust regression methods. General linear modelling was employed to investigate any effect of season and infection load on this condition measure. Potential impacts of multiple parasitism on the community, which have been largely overlooked in the literature, were first visually revealed by relating the levels of co-infections (in terms of prevalence and intensity) to the seasons. Then, a correlation analysis was carried out between condition estimates and the log-ratios of relative abundances of parasite groups. The results showed that mullets suffering from Monogenea-Digenea-Acanthocephala (M-D-A) and also along with Copepoda (M-D-A-C) co-infection had weights less than expected (K-n<1) under winter conditions. However, Trichodina involved co-infections appeared to prefer large sized hosts (K-n>1) particularly in autumn.