Context-dependent fright reactions in captive European minnows: The importance of naturalness in laboratory experiments

The responses of ostariophysan fish to alarm substance (Schreckstoff) have been investigated extensively in the laboratory but there have been few tests of its role under natural conditions. Furthermore, existing studies of the efficacy of Schreckstoff as an alarm substance in the wild have typically employed indirect approaches and have failed to document specific behaviour in a quantitative manner. European minnows, Phoxinus phoxinus, were exposed to Schreckstoff in small aquaria. They responded with a suite of behavioural changes that are consistent with the explanation that they perceive danger. Fish from the same population were then exposed to Schreckstoff under conditions that more closely resembled their natural habitat. Under these near-natural conditions they showed a small decrease in feeding rate and a slight increase in group size, both effects being transitory and independent of stimulus concentration. These data reveal that the ostariophysan fright reaction is context-dependent and highlight the importance of quantifying the behaviour of fish exposed to Schreckstoff under fully natural conditions.