Effect of the tapeworm Ligula pavlovskii on the life-history of the alien monkey goby (Neogobius fluviatilis)

The life-history traits of fish are influenced by numerous factors, including parasitic infections. Parasites can significantly impact host mortality, growth performance, and reproductive success. This study examines the effects of the parasite Ligula pavlovskii (Diphyllobothriidae) on its host, the monkey goby ( Neogobius fluviatilis ), in Lake Balaton, Hungary. Both species originated in the Ponto-Caspian region, with the fish arriving in the 1970s and the parasite following in the 2000s. Our research reveals substantial impacts of L. pavlovskii on the life history of the monkey goby, including differences in somatic (condition, length) and reproductive (gonadosomatic index, fecundity, egg size) investments between infected and non-infected individuals. Condition declined with higher parasite index in infected individuals. Female GSI was influenced by both parasite presence and severity of the infection, whereas male GSI was affected by the presence of the parasite. Additionally, the length frequency distributions of infected and non-infected fish showed seasonal differences, due to the bigger body size of infected individuals in summer and autumn. The high prevalence of the parasite and associated mortality resulted in a significantly reduced expected lifespan for infected fish. Our findings suggest that the competitive advantage of N. fluviatilis may be reduced when this fish is infected by L. pavlovskii . This should be considered when developing management interventions for this species.