Turbidity and predation risk: behavioural responses of a freshwater minnow

Abstract

High water turbidity, through its multifold influences on aquatic fauna, is considered a major cause of ecological concern. Here we examined the effects of elevated turbidity on the behaviour of a small cyprinid fish, the Stymphalia minnow, Pelasgus stymphalicus, using a combination of the well-established emergence, open field and predator response tests. Subjects from the two treatments differed in the way they emerged from an artificial refuge, with the turbidity-exposed fish being more hesitant. Moreover, these fish were also less active, had a lower propensity to explore and spent less time in the open centre of the test arena, compared to subjects tested in clear water. However, there was no effect of turbidity on the time fish spent immobile. Fish in both treatments responded strongly to a simulated predator attack from above. Turbidity decreased the time fish spent in the centre, the predator simulation decreased time spent immobile and both factors contributed to a decrease in activity, but without significant interaction effects. We discuss how turbidity may increase the perceived predation risk of these prey fish in our test conditions even in the absence of predator cues, as well as the implications of our findings for ecosystem management policy and conservation efforts targeting threatened freshwater fish species.