Behavioural responses of fathead minnows to carbohydrates found in aquatic environments.

Carbohydrates make up a significant portion of dissolved organic carbon in waterways. Apart from studies demonstrating that chondroitin causes avoidance behaviours in some fish species, no work has been done to determine how fish respond to carbohydrates commonly found in their environment. In this study fathead minnows (Pimephales promelas) were attracted to N-acetyl-d-glucosamine, avoided d-arabinose and had no response to either d-xylose or d-glucose using a behavioural assay. This study provides further evidence that carbohydrates may be important chemosensory cues for fish.

Effects of opioids on reproduction in Japanese medaka, Oryzias latipes.

To study the effects of exposure of fish to opioid drugs, we exposed Japanese medaka (Oryzias latipes) over a full life cycle to codeine spiked into river water at nominal concentrations of 100, 1,000 and 25,000 ng/L and to fentanyl spiked into river water at nominal concentrations of 5, 25 and 1,000 ng/L. The measured concentrations during medaka exposures were consistent with the nominal concentrations. Treatments with codeine at all test concentrations reduced the number of eggs produced by female medaka, as well as the number of mature oocytes observed histologically in the ovaries. Exposures to codeine also resulted in altered concentrations of hormones within the hypothalamic-pituitary-gonadal axis, including reduced levels of 17ß-estradiol in female medaka. Fentanyl did not affect reproduction or the levels of hormones in medaka at the concentrations tested. Monitoring of surface waters in southern Ontario, Canada downstream of wastewater treatment plants showed that the test concentrations of fentanyl and codeine were environmentally relevant. The results of this work contribute to the literature on the impacts of opioids and other drugs of abuse released into surface waters.