Comparative studies on goby (Teleostei) parasite communities from the North and Baltic Sea

Immigrant reproductive dysfunction facilitates ecological speciation

The distributions of species are not only determined by where they can survive - they must also be able to reproduce. Although immigrant inviability is a well-established concept, the fact that immigrants also need to be able to effectively reproduce in foreign environments has not been fully appreciated in the study of adaptive divergence and speciation. Fertilization and reproduction are sensitive life-history stages that could be detrimentally affected for immigrants in non-native habitats. We propose that "immigrant reproductive dysfunction" is a hitherto overlooked aspect of reproductive isolation caused by natural selection on immigrants. This idea is supported by results from experiments on an externally fertilizing fish (sand goby, Pomatoschistus minutus). Growth and condition of adults were not affected by non-native salinity whereas males spawning as immigrants had lower sperm motility and hatching success than residents. We interpret these results as evidence for local adaptation or acclimation of sperm, and possibly also components of paternal care. The resulting loss in fitness, which we call "immigrant reproductive dysfunction," has the potential to reduce gene flow between populations with locally adapted reproduction, and it may play a role in species distributions and speciation.

A revision of the genus Aphalloides (Digenea: Cryptogonimidae), parasites of European brackish water fishes

Trematodes of the genus Aphalloides Dollfus, Chabaud & Golvan, 1957 reach maturity in their second intermediate host, small fishes of the family Gobionellidae, genera Pomatoschistus and Knipowitschia. Two morphologically similar species have been described from European waters: Aphalloides coelomicola Dollfus et al., 1957 in the Mediterranean Sea (including the brackish Black Sea region) and Aphalloides timmi Reimer, 1970 in the Baltic Sea. There was no difference in morphology and morphometry for specimens corresponding to A. coelomicola and A. timmi and examination of the 28S rDNA sequence confirmed the similarity. Based on these results, these two species are synonymized and A. coelomicola redescribed.

Methodological issues affecting the study of fish parasites. II. Sampling method affects ectoparasite studies

In this study, we assessed the impact of sampling method on the results of fish ectoparasite studies. Common roach Rutilus rutilus were sampled from the same gravel pit in the River Dyje flood plain (Czech Republic) using 3 different sampling methods, i.e. electrofishing, beach seining and gill-netting, and were examined for ectoparasites. Not only did fish caught by electrofishing have more of the most abundant parasites (Trichodina spp., Gyrodactylus spp.) than those caught by beach seining or gill-netting, they also had relatively rich parasite infracommunities, resulting in a significantly different assemblage composition, presumably as parasites were lost through handling and 'manipulation' in the net. Based on this, we recommend electrofishing as the most suitable method to sample fish for parasite community studies, as data from fish caught with gill-nets and beach seines will provide a biased picture of the ectoparasite community, underestimating ectoparasite abundance and infracommunity species richness.

Diet composition and feeding ecology of the naked goby Gobiosoma bosc (Gobiidae) from four western Atlantic estuaries

The feeding ecology of the small-bodied benthic naked goby Gobiosoma bosc, a western Atlantic species that occurs in estuaries and other inshore habitats from Connecticut to Texas U.S.A., was investigated in a total of four estuaries spanning South Carolina, North Carolina, Maryland and New Jersey. Gut content analysis of 391 individuals revealed that G. bosc is a benthic microcarnivore that feeds primarily on polychaetes, gammarid amphipods and harpacticoid copepods. Diet composition varied with body size, tidal creek within an estuary and geographic region. Analyses of gut fullness suggest that G. bosc is a daytime visual predator and that nest and egg guarding during the reproductive season reduce foraging activity in mature males. Additionally, G. bosc infected with adult digenean parasites of the gut foraged more intensely than uninfected individuals, a relationship that was strongest for reproductively mature males. Regionally, significant variation in dietary breadth was documented and may reflect a foraging response to a decrease in prey diversity moving from estuaries of higher salinity and lower latitude to estuaries of lower salinity and higher latitude. These results contribute to an understanding of the life history of G. bosc and the role played by this common species in estuarine food webs.