Do potential predators induce an avoidance response in Daphnia carinata?

Abstract

Chemicals exuded by predators (kairomones) are known to induce the daytime descent of several species of Northern Hemisphere Daphnia. The vertical migration of New Zealand's native Dapknia carinata King has not been studied, however, and its response to kairomones is not known. We compared the behavioural responses of D. carinata to water from around two predatory fish, common bully (Gobiomorphus cotidianus) and inanga (Galaxias maculatus), an aquatic insect (Anisops wakefieldi), and several concentrations of trimethylamine (TMA), a fish‐mediated chemical. The responses of Daphnia were assessed in nine trials by comparing their vertical distribution in cylinders of water before and after exposure to water that had contained each predator, or TMA. D. carinata did not alter their vertical distribution in response to water from around Anisops. However, they descended when exposed to water from around inanga in 83% of trials and common bully in 67% of trials. They also descended in response to TMA in the range, 112.5–500 μM. Analysis of these “fish waters” failed to detect TMA at ≥ 20 μM, so that we cannot conclude that the behavioural cue from these fish is TMA.