Diel vertical migration (DVM) is a widespread predator‐avoidance behavior in Daphnia and can be induced by kairomones released by fish. It has recently been shown in laboratory experiments that DVM in Daphnia hyalina can be induced by micromolar concentrations of trimethylamine (TMA). The authors concluded, after spectrophotometrical determination of the amine content in fish incubation water, that TMA is an active component of the kairomone. Using a selective solid phase microextraction (SPME)/GCMS method, we show that the TMA content in fish incubation water was overestimated by several orders of magnitude. The amounts of TMA released by any of the three cyprinids Leuciscus idus, Leucaspius delineatus, and Carassius carassius have no relevance for DVM induction and TMA concentrations detected in fish incubation water did not induce DVM. Further, we show that efficient removal of existing TMA traces from fish incubation water did not decrease the kairomone activity. This excludes TMA as part of a kairomone cocktail. Hence TMA must not be called a kairomone in the fish‐Daphnia context.