Minnow traps

Setting minnow traps baited with chemical lure for attracting predatory fish (top), and emptying trap into plastic bag for identification of fish caught overnight... 

Brook stickleback and fathead minnows occupy the same habitat and are vulnerable to common predators. Individuals that detect alarm cues of co-habiting species may benefit by gaining early warning of danger. A field study by Mathis and Smith (1993) demonstrated that skin extract from fathead minnows is effective at inducing avoidance responses by stickleback. Brook stickleback exploit the alarm system of minnows and thus reduce their own risk of predation (Mathis and Smith, 1993 Wisenden et al., 1994). In a trap experiment by Wisenden et al. (1994), the duration of area avoidance by brook stickleback of areas marked with fathead minnow alarm substance was measured. They found that stickleback continued to avoid locations associated with predation risk after the source of the cue was removed, and only after 2-4 hours did the fish resume use of these risky areas. In a follow-up experiment, Wisenden et al. (1995) determined that fishes naive to the association of an area with alarm cue were the first to migrate into the risky area. Fishes present at the time of cue release did not return for 7 to 8 hours after the cue was removed. Perhaps the chief beneficiaries of chemical alarm cues are only those individuals present at the time of cue release. 

Trap experiments have also been used to determine the chemical composition of Ostariophysan alarm cues. In a study by Brown et al. (2000), traps labeled with fathead minnow extract, hypoxanthine-3-N-oxide or pyridine-N-oxide caught significantly fewer fishes (including dace and minnow) than those labeled with distilled water. These field results validate the outcome of laboratory studies in which significant increases in antipredator behavior in both fathead minnows and finescale dace were observed when they... 

In summary, most published trap experiments have shown that brook stickleback avoid fathead minnow or stickleback skin extract over distilled water (Wisenden et al., 1994 Chivers and Smith, 1994c Wisenden etal., 1995 Mathis and Smith, 1992, 1993). Similarly, fathead minnows avoid stickleback and minnow cues over distilled water (Wisenden et al., 1995 Mathis and Smith, 1992 Brown et al., 2000). While novel and informative, these studies have the drawback of using distilled water as the only control. 

One such study (Chivers et al., 1995) tested the response of two populations of minnows to traps labelled with either darter skin extract (Etheostoma exile) or swordtail skin extract (control). One population of fathead minnows was sympatric with darters, while the other was allopatric. In the darter-sympatric population, significantly fewer and smaller minnows were captured in traps marked with darter skin extract than traps marked with the control. In the darter-allopatric populations there was no difference in the number or size of minnows captured in experimental versus control traps. These results indicate that fathead minnows recognize and avoid areas where darter alarm cues are detected and that this may be a learned response. 

Table 1. Summary of fathead miimow Pimephales promelas) response in trap experiments (SB=stickIeback FHM=fathead minnow SWT=swordtail DW=distilled water).

In an attempt to verify the visual compensation model in the field, a day/night trap experiment was conducted by Kusch et al. (unpublished) on an established community of fathead minnows and brook stickleback. The Kusch et al. study found no interaction between light intensity and treatment. The light level did not affect the avoidance pattern of either species to the various concentrations of fathead minnow alarm cue. 

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