Effects of environmental exposure to diazepam on the reproductive behavior of fathead minnow, Pimephales promelas

Abstract

Pharmaceutical drugs are continuously discharged into the aquatic environment primarily through wastewater discharge; therefore, their possible effects on wildlife is a reason of concern. Diazepam is a widely prescribed benzodiazepine drug used to treat insomnia and anxiety disorders, and it has been found in wastewater effluents worldwide. The present study tested the effects of diazepam on fecundity and the reproductive behavior of the fathead minnow, Pimephales promelas, a fish that exhibits male parental care. Sexually mature fathead minnows were housed at a ratio of one male and two females per tank and exposed to nominal (measured) concentrations of 0, 0.1 (0.14 ± 0.06), 1.0 (1.04 ± 0.15), 10 (13.4 ± 1.5) µg L(-1) for 21 days. Fish receiving the low diazepam treatment had significantly larger clutches than fish receiving the highest concentration but neither were different from controls. Diazepam exposure was not associated with a significant change in fertilization rate, hatchability or time to hatch, but a trend toward a higher number of eggs/day was observed in fish exposed to the low diazepam concentration relative to those exposed to the medium concentration. There were no significant differences in any of the behaviors analyzed when responses were averaged over time. The results showed that exposure to diazepam at concentrations as high as 13 µg L(-1) did not significantly impact the reproductive behavior of fathead minnow.

Effects of the anxiolytic benzodiazepine oxazepam on freshwater gastropod reproduction: a prospective study

“…Furthermore, the fecundity of R. balthica does not seem to be disturbed by oxazepam exposure. Similar observations have already been reported for fathead minnows exposed to diazepam (Lorenzi et al, 2014). However, it should be noted that hatching rates in control and the lowest concentration were significantly lower than expected.…”

“…Anxiolytics are known to affect mammalian reproduction (Drobnis and Nangia, 2017;Guerriero and Fox, 1976;McElhatton, 1994), but surprisingly little is known about their toxicity to aquatic organisms. A few studies have shown that diazepam decreases social interactions in zebrafish (Danio rerio) (Giacomini et al, 2016), but no significant impact of this drug on reproductive behavior in fathead minnow (Pimephales promelas), or of oxazepam in Atlantic salmon (Salmo salar) (Hellström et al, 2020;Lorenzi et al, 2014) was reported. In addition, exposure to carbamazepine and diazepam has been shown to increase the total number of offspring in Daphnia magna (Rivetti et al, 2016).…”

Low concentrations of the benzodiazepine drug oxazepam induce anxiolytic effects in wild-caught but not in laboratory zebrafish

“…In zebrafish (Danio rerio) such novel tank diving test results would be considered indicative of an increased anxiety-like state and/or a sedative effect (Cachat et al, 2010), but as the authors point out, fathead minnows may not respond in the same way (Huerta et al, 2016). Reproductive behavior of fathead minnows appears unaffected by a 21-day exposure to diazepam (0.1, 1.04 or 13.4 µg L -1 ) (Lorenzi et al, 2014). Taken together, these studies provide evidence that oxazepam can induce anxiolytic effects in wild fish populations close to WWTP outlets, although species differ in sensitivity.…”

Social status modulates the behavioral and physiological consequences of a chemical pollutant in animal groups

“…For instance, Lorenzi et al. 2016 found that fathead minnow ( Pimephales promelas ) reproduction was increased when fish were exposed to 0.1 µg/L of diazepam and not the higher doses. It is clear that plasma cortisol, one mechanism by which oxazepam may induce its effects.…”