The costs and benefits in an unusual symbiosis: experimental evidence that bitterling fish (Rhodeus sericeus) are parasites of unionid mussels in Europe

Interspecific symbiotic relationships involve a complex network of interactions, and understanding their outcome requires quantification of the costs and benefits to both partners. We experimentally investigated the costs and benefits in the relationship between European bitterling fish (Rhodeus sericeus) and freshwater mussels that are used by R. sericeus for oviposition. This relationship has hitherto been thought mutualistic, on the premise that R. sericeus use mussels as foster parents of their embryos while mussels use R. sericeus as hosts for their larvae. We demonstrate that R. sericeus is a parasite of European mussels, because it (i) avoids the cost of infection by mussel larvae and (ii) imposes a direct cost on mussels. Our experiments also indicate a potential coevolutionary arms race between bitterling fishes and their mussel hosts; the outcome of this relationship may differ between Asia, the centre of distribution of bitterling fishes, and Europe where they have recently invaded.

The distribution of monogenean parasites on aquatic vertebrates inhabiting Chinese inland waters

The general distribution of monogenean parasites of aquatic vertebrates inhabiting Chinese inland waters is summarised. Five hundred and seventy-two out of a total of 581 species of monogeneans were discovered on fish, while only nine species were found on Amphibia and Reptilia. Most dactylogyrids and diplozoids parasitise cyprinids, while ancyrocephalids occur on silurids and cyprinids, and gyrodactylids are found mainly on cyprinids and cobitids. Analyses of host-specificity and host-diversity suggests that the family Ancyrocephalidae should be divided into several families parallel with the Dactylogyridae. Of 12 subfamilies of the Cyprinidae, only the Gobiobotinae was found to be free of infection with monogeneans, and the genus Dactylogyrus has more species than any other monogenean genus associated with every cyprinid subfamily.

Description of a new genus and two new species of Ioninae (Isopoda : Epicaridea : Bopyridae) parasites of Leucosiidae (Decapoda : Brachyura) from Beibu Gulf

A new genus, Onkokepon n. gen., and two new species, O. articulatus n. sp. and O. beibuensis n. sp., infesting Leucosia longibranchia Shen & Chen and Leucosia unidentata de Haan, respectively, are described from Beibu Gulf in China and Vietnam. Neither of these species of Leucosia has previously been reported as bopyrid hosts. The new genus differs from other ionine bopyrid genera in the presence of a well-developed tubercular frontal lamina, a deeply digitate barbula, rudimentary subcircular pleopodal endopodites, and lacking coxal plates. O. articulatus n. sp. is distinguished from O. beibuensis n. sp. by having articulated maxillipedal palp, blunt posterolateral point of oostegite 1 and setose triangular frontal lamina of the female.