Phylogenetic Affinities and Infection Patterns of Goussia Infecting Sardina pilchardus from the NE Atlantic.

Purpose European pilchard (Sardina pilchardus) is a highly valued fish in many European countries, particularly in Portugal. Despite current stock declines and the threats coccidia pose to European pilchards (e.g. castration), little is known about coccidian parasites infecting pilchards captured off the Portuguese coast. Methods In this study, we analyzed the infection patterns, the morphology of oocysts and the phylogenetic relations of coccidian parasites from European pilchard captured in Northern Portugal. Results Only Goussia oocysts were detected in infected tissues and prevalence of infection was 64% (n = 61). Oocysts were detected primarily in the liver with fewer infections in the stomach, intestine and gonads. No differences were found in the prevalence between seasons. Phylogenetic analysis showed these parasites are closely related to Goussia clupearum, placing them within a recently described group of Goussia, the clupearum type. Conclusions Our study provides more data on Goussia from the clupearum type with phylogenetic analysis indicating that these parasites cluster according to fish host taxonomy, thus suggesting some degree of co-evolution.