Chris N. Glover

Agricultural pesticides can enter freshwater systems through leaching, impacting non-target aquatic biota. Nanopesticides, such as copper nanoparticles (CuNPs), are promoted as cost-effective alternatives due in part to their more targeted delivery; however, their unique and often unpredictable behaviour raises concerns about environmental fate and toxicity. This study aimed to compare acute and chronic toxicity of CuNPs with that of a Cu salt (CuSO4·5H2O), using the model freshwater invertebrate Daphnia magna. Suspensions of CuNPs aggregated over time, complicating toxicity assessment. The observed acute 48-h median lethal concentration (LC50) for Cu was 31.2 μg/L (95% CI 27.6-36.0), while only partial mortality was observed for CuNP exposures. Cu exposures also elicited higher toxicity to D. magna over chronic 21 day exposures. Significant effects of chronic Cu exposure included a reduction in moults and an increase in daphnid metabolic rate, relative to the control. Despite the use of elevated exposure concentrations relative to Cu treatment groups, there were no significant effects of CuNPs on most measured endpoints, with the exception being a stimulation in average neonate production at an intermediate CuNP test concentration. These data indicate that CuNP treatments are less toxic to D. magna compared to Cu treatments, suggesting that the use of CuNPs may be advantageous in reducing non-target toxicity to aquatic biota.

A functioning digestive system requires the integration of many organ systems. In hagfishes, by virtue of their unusual digestive physiology, some of these integrative processes differ from those of other vertebrate groups, while the gut itself can have important roles in the function of other body systems. The digestive physiology of hagfishes is particularly influenced by their ecology and their feeding behaviour as scavengers that routinely feed on dead and decaying matter on the ocean floor. In this Commentary, we investigate the integration between the gut of hagfishes and the nervous, muscular, endocrine, immune, ionoregulatory and excretory, cardiovascular, respiratory and integumentary systems, emphasising the sui generis nature of the hagfishes. We also highlight the important consideration of the hagfish phylogenetic position and whether traits are of a primitive or derived nature, leading to different interpretations of digestive physiology in the context of functional evolution or adaptation to unique feeding lifestyles. We highlight putative areas of future investigation that will enhance not only our understanding of hagfish themselves but also the evolution of the highly integrative process of digestion.

Environmental deoxyribonucleic acid (eDNA) assays represent a non-invasive approach for biomonitoring. To assess Arctic grayling ( Thymallus arcticus, Pallas, 1776) populations in the Little Nahanni watershed of Northwest Territories, Canada, an eDNA assay that has been previously validated for use in fish of the Beringia lineage was used in conjunction with traditional survey methods (i.e., electrofishing). Forty-six 100 m reaches of streams were assessed in August 2015. The assay successfully detected Arctic grayling of the Nahanni lineage, with an eDNA signal recorded at each of the 17 sites in which Arctic grayling were observed by traditional fish surveys, but also at 3 of the 29 sites where Arctic grayling were not observed. The presence of eDNA was related to habitat metrics via Random Forest and correlation analyses. Riffles and water temperature were identified as being predictive of Arctic grayling eDNA abundance; however, no significant relationship between eDNA abundance and biomass proxies (fish abundance and fork length metrics) could be established. The high congruence between traditional approaches and eDNA surveys suggests adoption of the latter method will enhance the temporal and spatial acuity of biomonitoring, thereby improving field assessment of Arctic grayling populations and contributing towards more effective conservation management of this species.

Concentrations of selenium that exceed regulatory guidelines have been associated with coal mining activities and have been linked to detrimental effects on aquatic ecosystems and the organisms therein. Although the major route of selenium uptake in macroinvertebrates is via the diet, the uptake of waterborne selenite (HSeO₃⁻), the prominent form at circumneutral pH, can be an important contributor to selenium body burden and thus selenium toxicity. In the current study, radiolabelled selenite (Se⁷⁵) was used to characterize the mechanism of selenite uptake in the water flea, Daphnia magna. The concentration dependence (1–32 μM) of selenite uptake was determined in 1-hour uptake assays in artificial waters that independently varied in bicarbonate, chloride, sulphate, phosphate and selenate concentrations. At concentrations representative of those found in highly contaminated waters, selenite uptake was phosphate-dependent and inhibited by foscarnet, a phosphate transport inhibitor. At higher concentrations, selenite uptake was dependent on waterborne bicarbonate concentration and inhibited by the bicarbonate transporter inhibitor DIDS (4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid). These findings suggest that concentrations of phosphate in coal mining-affected waters could alter selenite uptake in aquatic organisms and could ultimately affect the toxic impacts of selenium in such waters.