Alarm pheromones fright reactions

In minnows, taste is not sufficient for predator recognition. Anosmic fathead minnows, P. pmmelas, did not show the flight reaction to the odor of northern pike, Esox lucius (Chivers and Smith, 1993). Naive European minnows, Phoxinus phoxinus, do not exhibit a fright reaction when first exposed to a predator odor, such as that of pike, E. lucius. They develop a conditioned fright response only after experiencing the predator odor in dangerous circumstances, such as when accompanied by schreckstoff (alarm pheromone) of conspecifics. Responses to the odor of non-piscivorous fishes such as tilapia, Tilapia mariae, can also be conditioned in this fashion but the responses are much weaker (Magurran, 1989). 

The effectiveness of the overt fright reaction as defense has been demonstrated in fathead minnows Pimephales promelas) where the overt responses decrease an individual s vulnerability to predation by pike in laboratory tanks (Mathis Smith 1993b). There is also evidence that the overt responses are often contingent on other variables. For example, both Iowa darters (Etheostoma exile) (Smith 1981), which are not ostariophysans, and fathead minnows, which are, (Brown Smith 1996) show a reduction or absence of overt responses when foraging tradeoffs are increased by 48 hours of food deprivation. Common shiners Luxilus cornutus) vary their responses to alarm pheromones according to whether they detect an aquatic or avian predator in the vicinity (Heczko 1980). 

Both Reed et al. (1972) and Ruddy and Baeder (1973) elicited fright reactions with histamine but histamine is present in all vertebrates while the alarm pheromone is specific to ostariophysans. Histamine "Occurs widely in nature as a result of putrefactive processes" (Stecher et al., p. 533, 1969). So the response reported by Reed et al. (1972) and Ruddy and Baeder (1973) may be an adaptive avoidance response to odours of putrefaction rather than a specific response to conspecific alarm pheromone. Neither group of researchers tested the response of non-ostariophysan fish to histamine. 

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