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Abstract

Fish can induce diel vertical migration behavior in different zooplankton species by exuding a chemical cue of an unknown nature. We present a standardized and reliable bioassay for the assessment of the kairomone. Using this tool, we show that the signal is released very quickly into the water and that it can be produced by different fish species of different trophic status. The production of the substance does not depend on the nutritional state of the fish. The active compound is water soluble and non-volatile, even though it has a low molecular weight (< 500 Dalton). It is stable under extreme temperatures and across a broad pH range. The activity is not digested by general peptidases Pronase E and Proteinase K, which suggests that it is not a protein. Under nonsterile conditions at 37-degrees-C it disappears within 24 h, whereas sterile treatment preserved its activity, indicating rapid microbial degradation.