Metabolomic-Based Comparison of Daphnia magna and Japanese Medaka Responses After Exposure to Acetaminophen, Diclofenac, and Ibuprofen.

Pharmaceuticals are found in aquatic environments due to their widespread use and environmental persistence. To date, a range of impairments to aquatic organisms has been reported with exposure to pharmaceuticals; however, further comparisons of their impacts across different species on the molecular level are needed. In the present study, the crustacean Daphnia magna and the freshwater fish Japanese medaka, common model organisms in aquatic toxicity, were exposed for 48 h to the common analgesics acetaminophen (ACT), diclofenac (DCF), and ibuprofen (IBU) at sublethal concentrations. A targeted metabolomic-based approach, using liquid chromatography-tandem mass spectrometry to quantify polar metabolites from individual daphnids and fish was used. Multivariate analyses and metabolite changes identified differences in the metabolite profile for D. magna and medaka, with more metabolic perturbations for D. magna. Pathway analyses uncovered disruptions to pathways associated with protein synthesis and amino acid metabolism with D. magna exposure to all three analgesics. In contrast, medaka exposure resulted in disrupted pathways with DCF only and not ACT and IBU. Overall, the observed perturbations in the biochemistry of both organisms were different and consistent with assessments using other endpoints reporting that D. magna is more sensitive to pollutants than medaka in short-term studies. Our findings demonstrate that molecular-level responses to analgesic exposure can reflect observations of other endpoints, such as immobilization and mortality. Thus, environmental metabolomics can be a valuable tool for selecting sentinel species for the biomonitoring of freshwater ecosystems while also uncovering mechanistic information. Environ Toxicol Chem 2024;43:1339-1351. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Exposure to exogenous egg cortisol does not rescue juvenile Chinook salmon body size, condition, or survival from the effects of elevated water temperatures.

Climate change is leading to altered temperature regimes which are impacting aquatic life, particularly for ectothermic fish. The impacts of environmental stress can be translated across generations through maternally derived glucocorticoids, leading to altered offspring phenotypes. Although these maternal stress effects are often considered negative, recent studies suggest this maternal stress signal may prepare offspring for a similarly stressful environment (environmental match). We applied the environmental match hypothesis to examine whether a prenatal stress signal can dampen the effects of elevated water temperatures on body size, condition, and survival during early development in Chinook salmon Oncorhynchus tshawytscha from Lake Ontario, Canada. We exposed fertilized eggs to prenatal exogenous egg cortisol (1,000 ng/ml cortisol or 0 ng/ml control) and then reared these dosed groups at temperatures indicative of current (+0°C) and future (+3°C) temperature conditions. Offspring reared in elevated temperatures were smaller and had a lower survival at the hatchling developmental stage. Overall, we found that our exogenous cortisol dose did not dampen effects of elevated rearing temperatures (environmental match) on body size or early survival. Instead, our eyed stage survival indicates that our prenatal cortisol dose may be detrimental, as cortisol-dosed offspring raised in elevated temperatures had lower survival than cortisol-dosed and control reared in current temperatures. Our results suggest that a maternal stress signal may not be able to ameliorate the effects of thermal stress during early development. However, we highlight the importance of interpreting the fitness impacts of maternal stress within an environmentally relevant context.

Metabolic Costs of Exposure to Wastewater Effluent Lead to Compensatory Adjustments in Respiratory Physiology in Bluegill Sunfish.

Municipal wastewater effluent is a major source of aquatic pollution and has potential to impact cellular energy metabolism. However, it is poorly understood whether wastewater exposure impacts whole-animal metabolism and whether this can be accommodated with adjustments in respiratory physiology. We caged bluegill sunfish (Lepomis macrochirus) for 21 days at two sites downstream (either 50 or 830 m) from a wastewater treatment plant (WWTP). Survival was reduced in fish caged at both downstream sites compared to an uncontaminated reference site. Standard rates of O2 consumption increased in fish at contaminated sites, reflecting a metabolic cost of wastewater exposure. Several physiological adjustments accompanied this metabolic cost, including an expansion of the gill surface area available for gas exchange (reduced interlamellar cell mass), a decreased blood-O2 affinity (which likely facilitates O2 unloading at respiring tissues), increased respiratory capacities for oxidative phosphorylation in isolated liver mitochondria (supported by increased succinate dehydrogenase, but not citrate synthase, activity), and decreased mitochondrial emission of reactive oxygen species (ROS). We conclude that exposure to wastewater effluent invokes a metabolic cost that leads to compensatory respiratory improvements in O2 uptake, delivery, and utilization.

An evaluation of behavioural endpoints: The pharmaceutical pollutant fluoxetine decreases aggression across multiple contexts in round goby (Neogobius melanostomus).

Fluoxetine (Prozac™) is designed to alter human behaviour; however, because many physiological pathways are conserved across vertebrates, this drug may affect the behaviour of fish living in fluoxetine-polluted environments. Although a number of studies have used behaviour to document the sub-lethal effects of fluoxetine, the repeatability of these effects across experiments, across behavioural contexts, and over different exposure durations are rarely considered. Here, we conducted two experiments and assessed how fluoxetine exposure affected a range of fitness-related behaviours in wild round goby (Neogobius melanostomus). We found that fluoxetine impacts round goby behaviour at high (40 µg/l) doses, but not at environmentally relevant low doses (1 µg/l). In both experiments, an acute 3-day exposure to fluoxetine reduced round goby aggression in multiple behavioural contexts, but had no detectable effect on overall activity or social affiliative behaviour. While a chronic 28-day exposure to fluoxetine exposure still reduced aggression, this reduction was only detectable in one behavioural context. Our findings demonstrate the importance of repeated behavioural testing (both between and within experiments) and contribute to a growing body of literature evaluating the effects of fluoxetine and other pharmaceuticals on animal behaviour.

In situ exposure to wastewater effluent reduces survival but has little effect on the behaviour or physiology of an invasive Great Lakes fish.

Treated effluents from wastewater treatment plants (WWTP) are a significant source of anthropogenic contaminants, such as pharmaceuticals, in the aquatic environment. Although our understanding of how wastewater effluent impacts fish reproduction is growing, we know very little about how effluent affects non-reproductive physiology and behaviours associated with fitness (such as aggression and activity). To better understand how fish cope with chronic exposure to wastewater effluent in the wild, we caged round goby (Neogobius melanostomus) for three weeks at different distances from a wastewater outflow. We evaluated the effects of this exposure on fish survival, behaviour, metabolism, and respiratory traits. Fish caged inside the WWTP and close to the outfall experienced higher mortality than fish from the reference site. Interestingly, those fish that survived the exposure performed similarly to fish caged at the reference site in tests of aggressive behaviour, startle-responses, and dispersal. Moreover, the fish near WWTP outflow displayed similar resting metabolism (O2 consumption rates), hypoxia tolerance, haemoglobin concentration, haematocrit, and blood-oxygen binding affinities as the fish from the more distant reference site. We discuss our findings in relation to exposure site water quality, concentrations of pharmaceutical and personal care product pollutants, and our test species tolerance.