Interspecific and Spatial Comparisons of Perfluorinated Compounds in Bighead and Silver Carp in the Illinois River, Illinois, USA.

We examined perfluoroalkyl compounds (PFC) in bighead (BHCP; Hypophthalmichthys nobilis) and silver (SVCP; H. molitrix) carp from the Illinois River, Illinois, USA. Summed PFC concentrations in whole fish did not differ by species or river reach. Perfluorooctanesulfonate (PFOS) concentrations were much greater in whole fish (16.4 ng/g) than in fillets (3.4 ng/g). PFOS concentrations represented 35%-51% of total measured PFC concentrations in whole fish, and in fillets were weakly associated with carcass mass (R2=0.17, p=0.01) and % carcass lipid (R2=0.16, p=0.01). No such relationship was observed in whole fish. The relationship between concentrations of individual PFC congeners in whole fish and carcass mass or % lipid content varied by species. Our study demonstrated that filter-feeders such as BHCP and SVCP can accumulate measureable concentrations of PFC and these results are important for understanding the fate of these compounds in large river systems.

Post-mating reproductive barriers in two unidirectionally hybridizing sunfish (Centrarchidae: Lepomis).

The evolutionary sequence of events in the evolution of reproductive barriers between species is at the core of speciation biology. Where premating barriers fail, post-mating barriers, such as conspecific sperm precedence (CSP), gamete incompatibility (GI) and hybrid inviability (HI) may evolve to prevent the production of (often) costly hybrid offspring with reduced fitness. We tested the role of post-mating mechanisms for the reproductive isolation between two sunfish species [bluegill (BG) Lepomis macrochirus and pumpkinseed (PS) Lepomis gibbosus] and their first-generation hybrids. Performing in vitro sperm competition experiments, we observed asymmetric CSP as main post-mating isolation mechanism when BG and PS sperm were competing for PS eggs, whereas when sperm from both species were competing for BG eggs it was HI. Furthermore, hybrid sperm--although fertile in the absence of competition--were outcompeted by sperm of either parental species. This result may at least partly explain previous observations that natural hybridization in the study system is unidirectional.

Nest-site fidelity in parental male bluegill Lepomis macrochirus: spatial patterns and the influence of prior mating success.

A 4 year mark-recapture study examined the pattern of nesting site fidelity of parental-type male bluegill Lepomis macrochirus. The study results indicated that iteroparous male L. macrochirus choose new nest sites near their own previously used sites. The scale of site fidelity varied, but generally males choose to renest within shoreline areas rather than specific or exact nest locations (94% within-year, 86% among-years). Iteroparous males also displayed no preference to nest in proximity to neighbouring males from previous colonies to suggest social fidelity. Contrary to expectation, manipulating males' reproductive success had no significant effect on the pattern or scale of male reproductive site fidelity.

Contaminant concentrations in Asian carps, invasive species in the Mississippi and Illinois Rivers.

Populations of invasive fishes quickly reach extremely high biomass. Before control methods can be applied, however, an understanding of the contaminant loads of these invaders carry is needed. We investigated differences in concentrations of selected elements in two invasive carp species as a function of sampling site, fish species, length and trophic differences using stable isotopes (delta (15)N, delta (13)C). Fish were collected from three different sites, the Illinois River near Havana, Illinois, and two sites in the Mississippi River, upstream and downstream of the Illinois River confluence. Five bighead carp (Hypophthalmichthys nobilis) and five silver carp (Hypophthalmichthys molitrix) from each site were collected for muscle tissue analyses. Freshwater mussels (Amblema plicata) previously collected in the same areas were used as an isotopic baseline to standardize fish results among sites. Total fish length, trophic position, and corrected (13)C, were significantly related to concentrations of metals in muscle. Fish length explained the most variation in metal concentrations, with most of that variation related to mercury levels. This result was not unexpected because larger fish are older, giving them a higher probability of exposure and accumulation of contaminants. There was a significant difference in stable isotope profiles between the two species. Bighead carp occupied a higher trophic position and had higher levels of corrected (13)C than silver carp. Additionally bighead carp had significantly lower concentrations of arsenic and selenium than silver carp. Stable isotope ratios of nitrogen in Asian carp were at levels that are more commonly associated with higher-level predators, or from organisms in areas containing high loads of wastewater effluent.