How a fish's personality determines the way it is caught


If you fish, then the next one you land with a rod and line may be a coward, according to research published in a recent issue of the Canadian Journal of Fisheries and Aquatic Sciences.

Alexander Wilson and colleagues made this discovery while testing the behaviour of Bluegill sunfish (Lepomis macrochirus) caught by using a seine and those caught by using a lure.

The authors caught 230 juvenile sunfish using both beach seines and lures from Lake Opinicon in Ontario. The fish were then placed in holding tanks before the first set of experiments were conducted.

In the first set of experiments, the sunfish were placed in a refuge portion of the experimental aquarium, which was separated from the rest of the aquarium (designated as the arena) by an opaque sliding door.  The door was then opened after a period of acclimation and the fish allowed to exit and explore the arena.

Each fish was observed for 20 minutes, during which behavioural measures associated with risk-taking (time taken to exit the refuge, use of the water column and total time spent active in the arena) were recorded.  

The fish that were caught using angling were then euthanised and their parasite load (i.e. the number of ectoparasites on each fish) measured.

The seined fish were then conducted to another series of experiments, in which eight groups of 15 fish each were placed in a large outdoor fibreglass pool and attempts were made to capture the fish using a standardised angling technique in which a baited hook was dangled in front of refuges placed in the tank (in which the fish were mostly congregating) for 20 minutes. This attempt was carried out three times a day, and equipment (hook and bait choice) was identical to that used in the initial capture of the fishes from the field.

The authors also measured the plasma cortisol (a common stress hormone in fishes) levels of fish caught by angling and by seine to ascertain whether the two methods of capture are associated with different levels of stress.

The authors found from their experiments that fish caught by seines were bolder (taking less time to emerge from refuge) and had more ectoparasites than those caught via angling. But there was no significant difference in water-column use and general activity between the two groups of fishes caught by different methods.

However, this relationship between boldness and angling did not carry over to their experiments in the outdoor pool (here the bolder individuals swimming more often in the open water were caught more often). There was also no significant difference in the plasma cortisol levels in the two groups of fishes, indicating that both angling and seining were equally stressful to the sunfish.

Although the findings were opposite to what the researchers had predicted (that bolder fish would be more often be caught from the lake by angling), the relationship they found appears to make ecological sense. Despite spending equal durations angling in open water and in areas with dense cover, the authors caught more fish in the areas with refuge, which is a habitat more appealing to timid fish. On the other hand, seining in open waters is more likely to target bolder, risk-taking fish.

The latter hypothesis is supported by the results of the outdoor pool experiment, where the bolder fishes more often encountered in open water were caught.

For more information, see the paper: Wilson, ADM, TR Binder, KP McGrath, SJ Cooke, J-GJ Godin and C Kraft (2011) Capture technique and fish personality: angling targets timid bluegill sunfish, Lepomis macrochirus. Canadian Journal of Fisheries and Aquatic Sciences 68, pp. 749–757.

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