Hydrobiology, Volume 4, Issue 1 (March 2025) – 7 articles

Muskellunge (Esox masquinongy) are a recreationally and ecologically important apex predator found throughout North America. In West Virginia, the genetic structuring and diversity of native muskellunge is poorly understood. The supplementary stocking of non-native muskellunge has further complicated the issue, as the introgression of non-native alleles and prevalence of non-native muskellunge post stocking remains unclear as well. Using ddRAD sequencing, several datasets were generated to investigate the population structure and genomic diversity of muskellunge in West Virginia. Populations stocked with New York-strain muskellunge exhibited significant introgression, with genetic composition diverging from unstocked native West Virginia populations. However, one population showed greater genetic similarity to native and unstocked populations despite New York-strain prevalence, suggesting resilience against genetic alteration. Fixed SNPs between the New York and West Virginia strains were identified that can be used for broodstock screening and the enhancement of native populations. A genetically distinct population was identified in the Little Kanawha River system, with this population having the highest levels of genomic diversity among native populations as well as a high number of private alleles. However, elevated inbreeding coefficients highlight potential conservation concerns for this unique population. This study establishes a genomic baseline for muskellunge in West Virginia and underscores the importance of preserving native genomic diversity while balancing the demands of recreational fishing programs. Full article

Systemic habitat destruction over the last 100 years combined with major anthropogenic stressors such as aquatic contaminants, exotic species, and economic endeavors is driving the decline in freshwater unionid species diversity. Global temperatures continue to increase, with January 2024 being the warmest on record according to the latest report by the World Meteorological Organization. Freshwater mussels play a crucial role in aquatic ecosystems, contributing significantly to benthic processes in rivers and streams, yet they remain highly sensitive to environmental changes. This study specifically investigates the thermal tolerance of the Texas pigtoe (Fusconaia askewi) under elevated temperature conditions and explores the implications for developing effective conservation strategies in freshwater ecosystems. Eighty-four individual adult Texas pigtoe mussels were collected from the upper Sabine River near Hawkins, Texas, and taken to the University of Texas at Tyler to evaluate the effects of elevated temperature, a likely factor impacting mussels in East Texas. In the thermal tolerance study presented here, 100% survival occurred at both the control (20 °C) and the 25 °C test points. The 30 °C treatment group had an overall mortality of 14% and the 35 °C treatment group showed a mortality rate of 43% by the end of the trial, suggesting the typical summer temperatures in Texas streams will result in the loss of a portion of an otherwise healthy population. Full article

Bisphenol A, BPA, is a small molecule frequently used in large-scale plastic production. The chemical has garnered a reputation for its association with harmful human health effects, and numerous animal studies have contributed to its classification as an endocrine disruptor. Prior research has investigated the impact of the chemical on echinoderms, including seven species of sea urchin. Our project investigated the toxic effects of this chemical on two uninvestigated species: Lytechinus variegatus and Arbacia punctulata. We exposed embryos to a range of environmentally relevant BPA concentrations (1 µg/L, 10 µg/L, 100 µg/L, and 1000 µg/L) for 48 h, until the pluteus stage. Larvae were classified according to the type of abnormality they exhibited, using a light microscope, and the EC50 was determined through probit analysis and dose–response curves. We also examined isolated plutei skeletons under a scanning electron microscope to assess changes to the skeletal structure under increasing concentrations of BPA. Our results suggest BPA induces embryotoxicity and soft tissue abnormalities more severely in L. variegatus, whereas A. punctulata exhibits more resistance to these effects. The EC50 values, over 1000 µg/L for A. punctulata and approximately 260 µg/L for L. variegatus, support this. These relative values also agree with our hypothesis that sea urchin embryos in a single genus have a similar level of BPA embryotoxicity. Interestingly, under SEM examination, the A. punctulata skeletal microstructure appears to be altered as a result of BPA exposure. While the EC50s are below what has been documented in many, but not all, marine environments, longer and consistent exposure may have a more deleterious impact. These findings suggest BPA’s effects on echinoderms should be further explored with multiple forms of analysis and over the long term. Full article

The present study aimed to describe the reproductive cycle of the black-footed limpet (Patella depressa Pennant, 1777) from an intertidal rocky shore on the Algarve coast (southern Portugal). Samples were collected monthly between January 2017 and December 2018, with the species’ gametogenic cycle being described based on gonad histology and the mean gonadal index. The presence of both transitional and mosaic hermaphrodites indicates that some individuals are able to change sex (sequential hermaphroditism). Despite the occurrence of hermaphroditism, sex proportions were approximately equal, suggesting the absence of protandric sex change in this species. The population exhibited an extensive occurrence of ripe and spawning gonads throughout almost the whole study period, probably related to consecutive processes of gonadal re-ripening and partial spawning events. The reproductive dynamics of P. depressa displayed clear inter-annual differences, with a short resting period recorded in 2017 (June–August) and the absence of resting gonads in 2018. The continued monitoring of this population and collection of environmental data are required to further improve knowledge of the reproductive dynamics of this species. Such information is crucial for proposing additional management measures for the sustainable harvesting of limpets in southern Portugal. Full article

Biologists commonly use standard sampling protocols to ensure that data are comparable spatiotemporally. Data also need to be precise to allow for statistically meaningful comparisons. However, the effort needed to precisely sample desert fishes is unclear. We used a resampling approach to evaluate the effort requirements needed to precisely sample fishes among six wadeable rivers in the Gila River basin, New Mexico. We evaluated the number of samples that are necessary to obtain relative density estimates that had 25% relative standard error 80% of the time. We also estimated the effort needed to precisely characterize species richness. Our results indicate that precisely sampling fish in the Gila River basin is difficult. Sonora Sucker Catostomus insignis, Desert Sucker C. clarkii, Longfin Dace Agosia chrysogaster, and Speckled Dace Rhinicthyes osculus were generally the only species that could be precisely sampled. Characterizing the native species assemblage in the Gila River basin required between two and seven reaches, whereas the entire species assemblage could only be characterized in 50% of the study systems. The challenge of precisely sampling fish in the Gila River basin suggests that alternative sampling methods may be required to characterize changes in density or species distribution in desert Southwest systems. Full article

Tannins are plant secondary compounds that leach into soil and water. Tannin concentrations can be higher in lentic freshwater than in other aquatic ecosystems, which can result in toxicity to freshwater organisms. While the amount of plant material and the plant tissue concentrations affect aqueous tannin concentrations, little is known about which environmental conditions alter the removal and breakdown of tannins in freshwater, altering the exposure of freshwater organisms. We investigated the effects of soil, light, and temperature on aqueous tannin concentrations. Tannins degraded faster in the presence of and/or sorbed to wetland soils, silt, and clay but not sand. It is unclear whether finer soil particles or the chemical makeup of soils facilitated sorption and/or degradation. Contrary to previous work, we found no effect of ambient light over a 14-day period or sunlight over a 7-day period on tannin degradation, but tannins degraded faster in warmer water. Warmer freshwater ecosystems with greater silt or clay sediments are likely to have lower aqueous tannin concentrations with lower toxicity to aquatic organisms. This research used tannic acid, which contains gallotannins. Further research is needed to determine if similar patterns are found with other tannin types and the complex mixtures of different tannins found in most plants. Full article

An important top-down predator, the northern pike (Esox lucius), faces harsh environmental conditions in the northern boreal ecoregion. They are often managed for recreational fishing and, more recently, to create environmental offsets; strategies aimed at balancing ecological impacts by enhancing or restoring habitats. Our study examines northern pike populations in two remote boreal lakes in northern Alberta: Steepbank and Wappau. The lakes differ in size, vegetation cover, and trophic status, providing a natural experiment for investigating northern pike growth, condition, diet, and population density. Over three years (2018–2020), northern pike were sampled using gill nets. Population metrics, including growth, condition, and stomach contents, were compared between the lakes. Steepbank, a smaller, oligotrophic lake with low vegetation cover, showed lower prey fish densities compared to the larger, eutrophic Wappau, but it did not differ in northern pike catch per unit effort. Growth rates and body condition varied significantly between the lakes, with the northern pike in Wappau exhibiting faster growth and a better condition in the older age groups, while the younger northern pike in Steepbank had higher relative weights. A diet analysis revealed significant differences in prey consumption: Steepbank northern pike displayed higher rates of conspecific predation and invertebrate consumption, particularly in the younger age classes. These findings highlight how lake characteristics and prey availability shape northern pike population dynamics, offering valuable insights for lake management approaches in northern Alberta. Full article