Sensitivity of northern redbelly dace, Phoxinus eos, to chemical alarm cues

Abstract

The northern redbelly dace, Phoxinus eos (Cope, 1862), is subject to predation by brook trout, Salvelinus fontinalis (Mitchill, 1814), in Canadian Shield lakes, particularly when individuals migrate to the pelagic zone at sunset to feed on zooplankton and fish shoals break up into single individuals. The objectives of the present study were to (i) determine whether northern redbelly dace react to skin extracts from conspecifics and thus potentially use chemical alarms to detect predators in nature, (ii) characterize the fright reaction in northern redbelly dace under different concentrations of alarm substance, and (iii) estimate the active space of the alarm substance in this species. Northern redbelly dace responded to skin extracts of conspecifics with a series of antipredator behaviours. The dace moved closer to the substrate and away from the area where the alarm substance was injected, increased both the cohesion and polarization of their schools, and performed more dashing and freezing behaviours. The observed responses were closely correlated with the concentration of the skin extract solution, suggesting that individuals could use this sensitivity to different concentrations of alarm substance to estimate the risk of predation in nature. The dilution experiment allowed us to estimate that 1 cm2 of northern redbelly dace skin contains enough alarm substance to generate a response of individuals in 110 558 L of water, which corresponds to a cube with sides of approximately 4.8 m. Indirect evidence suggests that the northern redbelly dace could use chemical alarm cues to assess the risk of predation by brook trout in nature.