Prey fish, predator odors

Prey fish may mask their own odors. Some marine fish avoid predation by covering their body odors. Some parrot fish (Scaridae) sleep in a mucus cocoon. It is believed that this covers up its scent and protects it from predation. Table 12.1 summarizes some chemical predator-prey relationships in marine fish. 

Fish avoid more vigorously the odor of predators that have fed on members of their species than that of those on different diets. For example, young Arctic chart avoid water from brown trout fed on Arctic chart and are less wary of that from pellet-fed trout (Hirvonen et ah, 2000). Prey fish also reduce their predator inspection behavior vis-a-vis predators that have eaten members of their own species. For instance, finescale dace, Phoxinus neogaeus, dash toward predators such as yellow perch, Percaflavescens, and withdraw. Dace inspect perch models less often if the model is accompanied by water from perch that had eaten dace than if accompanied hy water from perch on a swordtail, Xiphophorus hdleri, diet. Dace produce alarm pheromone, while swordtails do not. The Central American swordtails do not cooccur with finescale dace (Brown etal, 2001). 

Other fish species do not respond to predator odors. The threadfin shad, Doro-soma petenense, is strongly attracted to odors of its prey such as brine shrimp [Artemia) or Daphnia spp. but does not respond to those of its predator, the large-mouth bass, M. salmonides, or conspecifics. Both shad and bass swim faster than chemicals travel in water, which may explain this behavior difference (McMahon and Tash, 1979). 

The responses of the amphipod Gammarus minus to the odor of injured con-specifics resulted in an increase in the time until first attack by a fish predator (Wisenden et al. 1999). This delay should enhance the chances of prey to escape. The induction of a morphological change, spine development, in Daphnia by detection of predator odor results in increased chance of escape once attacked (Havel and Dodson 1984). The brachyuran crab //. rotundifrons responds to cues indicating increased predation risk by assuming an immobile, appendage-extended posture (Fig. 18.1). This posture mechanically inhibits predation by fish (Hazlett and McLay 2000) and exposure to the odor of crushed conspecifics increases the duration of this defensive posture. 

Predatory fish may also be affected by alarm pheromones (Section 7.2) of the prey, both directly and indirectly. The alarm odor may act as defense compoimd that inhibits predator attack or reduces capture rate by inducing predator avoidance in school members of the prey species. 

Several fish and crustacean species use chemical alarm cues to avoid predators. The odors are either released by damaged conspecifics or in the feces by the predator preying on the fish or crustacean species (e.g. Ferrari et al. 2007 Hazlett, Chap. 18). Detection of predators is under strong selection as it is important for prey to be able to detect, avoid the predator and assess the risk of being in a certain environment. 

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