David P. Coulter

Intersex in fishes and amphibians: population implications, prevalence, mechanisms and molecular biomarkers.

Intersex is defined as the abnormal presence of both testicular and ovarian cells in gonads of gonochoristic animals. Its occurrence is widespread and reports on its presence in the gonads of vertebrates continues to increase. In this review, we use standardized terminology to summarize the current knowledge of intersex in gonochoristic fishes and amphibians. We describe the different indices that have been used to assess the severity of intersex and synthesize reports discussing the prevalence of intersex in relation to different types of pollutants. In addition, we evaluate the geographic distribution and chronology of the reported cases of intersex in fishes and amphibians, their pathological descriptions and severity and discuss species sensitivities. We also summarize molecular biomarkers that have been tested for early detection of intersex in wild populations and highlight additional biomarkers that target molecular pathways involved in gonadal development that require further investigation for use in the diagnosis of intersex. Finally, we discuss the needs for future research in this field. Copyright

Effects of dreissenid mussels, chironomids, fishes, and zooplankton on growth of round goby in experimental aquaria

There is a widely accepted paradigm supported by early field and laboratory observations that the adult round goby (Neogobius melanostomus) is highly adapted to, and primarily survives on, dreissenid mussels. However, more recent stable isotope and diet analyses indicate that the round goby may not rely on dreissenid prey to the extent that was previously believed. We conducted a feeding experiment where round gobies were provided with an excess of one of four naturally occurring diets for 25 days – dreissenid mussels, juvenile fish, chironomids, or zooplankton. Round gobies fed dreissenids had significantly lower growth (−0.04 g day−1) than individuals fed fish and chironomids (0.13 g day−1) and displayed the same weight loss as round gobies fed only zooplankton. Although dreissenids are often consumed by round gobies, this likely happens only when more profitable prey such as fish and non-dreissenid invertebrates are lacking or difficult to capture. Additionally, field observations of round goby diets that have supported the paradigm may overestimate the importance of dreissenid prey due to the longer retention time of shells in round goby guts compared to other soft-bodied prey. Our results provide direct evidence supporting recent findings that dreissenid mussels may not be as essential to round goby survival as previously considered.

Fluctuating water temperatures affect development, physiological responses and cause sex reversal in fathead minnows.

Natural and human activities can result in both high temporal and spatial variability in water temperature. Rapid temperature changes have the potential to dramatically affect physiological processes in aquatic organisms and, due to their limited mobility, fish early life stages are particularly vulnerable to ambient temperature fluctuations. In this study, we examined how the magnitude and frequency of temperature fluctuations affect survival, growth, development, expression of thermoresponsive genes, and gonadal differentiation in fathead minnows, Pimephales promelas. We exposed individuals (0 to 4 days post fertilization) of known genotypic sex to fluctuations of Δ4 °C over 12-h, Δ8 °C over 12- and 24-h, and three stable temperatures (21, 25, and 29 °C) for up to 45 d. Expression of hsp70 in fish exposed to the highest-magnitude, highest-frequency fluctuating treatment cycled in concert with temperature and was upregulated initially during exposure, and may have contributed to temperature fluctuations having little effect on time to and size at hatching (whole-organism responses). This treatment also caused fish to undergo nondirectional sex reversal. These results indicate that hsp70 may be involved in mediating thermal stress from subdaily temperature fluctuations and that sex determination in fathead minnows can be influenced by cycling temperatures.

Does overwinter temperature affect maternal body composition and egg traits in yellow perch Perca flavescens

Female yellow perch Perca flavescens exposed to three overwinter temperature regimes (4, 8 and 13° C) for 150 days spawned in markedly different proportions upon spring warming (37% of females in 4° C v. 64 and 91% in 8 and 13° C treatments, respectively), but exhibited no differences in fecundity, egg size or egg lipid content. Females held at 4° C also exhibited less within-clutch egg size variation than females held at 13° C. Moreover, eggs differed among temperature treatments in the overall proportions of 18 fatty acids, with the colder treatments resulting in potentially higher quality eggs containing more of the unsaturated fatty acids C16:1, C22:6-n3 and C18:2 cis. Female somatic condition also varied with temperature. Maternal somatic growth and protein content increased while lipid content decreased in 13° C compared to the colder treatments. There were, however, no differences among treatments in the fatty acid composition of maternal muscle. These results suggest that the temperatures experienced during winter may be less influential to P. flavescens egg size or number, which may exhibit relatively little plasticity in this species, but can alter both the number of females that spawn and the overall composition of eggs and maternal somatic tissues, which may have implications for future reproductive success.

Environmental influences on fish assemblage variation among ecologically similar glacial lakes

The composition and structure of fish communities are affected by a variety of factors, both within the aquatic ecosystem and from the surrounding watershed. Many studies have examined what structures fish assemblages over broad spatial and environmental gradients. However, the influence of local environmental attributes on the observed variation in fish assemblages is less understood across finer spatial scales, where broad-scale climatic and anthropogenic factors are relatively similar. We used multiple linear regression to examine the relationships between environmental variables and various aspects of fish assemblages (including trophic function, community indices, and species composition) in 90 glacial lakes from northern Indiana, USA, from 1990 to 2010. Trophic structure and species composition were primarily related to water quality, whereas trophic level increased and omnivores declined as Secchi depth increased and phosphorus concentrations decreased. Species richness and diversity, in contrast, were positively linked to lake size and depth. We also found unique relationships among fish assemblages and environmental variables between samples collected using gill nets and night electrofishing, which may result from these gears sampling different assemblage components – therefore, relationships that were apparent in both sampling techniques (e.g., Secchi depth effects on trophic structure) may be the most robust and useful for improving aquatic ecosystem management on local scales.