Dietary selenomethionine exposure in adult zebrafish alters swimming performance, energetics and the physiological stress response

Selenomethionine (Se-Met) is the major form of organoselenium present in food. Early life stages of oviparous vertebrate species, especially fish, are highly susceptible to dietary selenium (Se) exposure; however less is known concerning effects in adults. The present study was designed to investigate behavioral and physiological consequences of dietary Se-Met exposure to adult zebrafish ( Danio rerio). Adult fish were fed either control food (1.3 μg Se/g, dry weight or dw) or food spiked with varying measured concentrations of Se (3.7, 9.6 and 26.6 μg Se/g, dw) in the form of Se-Met for 60 days at 5% body weight/day ration, and an additional 30–40 days with equal ration (2.5%) of control or Se-Met spiked foods and clean chironomids. At the end of the exposure period, critical swimming speed (Ucrit), oxygen consumption (MO 2), cost of transport (COT), tail beat amplitude, tail beat frequency, and whole body cortisol, triglyceride and glycogen levels were determined. Significantly reduced Ucrit was observed in fish fed 3.7, 9.6 and 26.6 μg Se/g when compared to control fish. Although MO 2 of fish fed >3 μg Se/g was consistently greater than control fish, those values were not statistically significant. There was no difference in COT among different treatment groups. Tail beat amplitudes of fish fed >3 μg Se/g were lower than control fish, however tail beat frequencies were not altered. Fish fed 3.7, 9.6 and 26.6 μg Se/g had greater whole body triglycerides and glycogen levels than control fish. Fish fed the highest concentration of Se (26.6 μg Se/g) had elevated levels of whole body cortisol compared to control fish. Our results suggest that environmentally relevant dietary Se-Met exposure can alter both behavioral and physiological responses in adult fish, and such consequences could threaten fitness of adult fish in Se impacted aquatic ecosystems.