Predator detection and learning capability in an endemic lake sucker

Background/Question/Methods The June Sucker (Chasmistes liorus) is a lake sucker, endemic to Utah Lake, Utah. In 1986 the June Sucker was federally listed as endangered with critical habitat. As part of the 1999 recovery plan, a large-scale restocking program has been instituted. The contribution of hatchery raised fish to the adult population is low. One possible explanation for this is a high level of predation by nonnative species. June Sucker are stocked into the lake at a length which leaves them vulnerable to predation by many of the introduced predators in Utah Lake, including Largemouth Bass (Micropterus salmoides). One characteristic of the super-order Ostariophysi, which contains June Sucker, is the ability to produce a chemical alarm cue which is released when the skin is ruptured during a predation event. Many studies have shown the ability of predator-naive fish to recognize predator odors as a threat after one exposure in conjunction with conspecific alarm cues. Survival may be improved if hatchery raised June Sucker can be trained to recognize predator odors prior to stocking. Increased survival may result in elevated numbers of adult fish in the spawning run, resulting in higher levels of recruitment. We measured the behavioral response of hatchery raised June Sucker exposed to four different stimuli. These stimuli are: 1) Largemouth Bass odor collected from fish fed exclusively June Sucker; 2) Largemouth Bass odor collected from fish fed exclusively Swordtail (a fish not known to produce an alarm cue); 3) alarm cue collected directly from June Sucker; and 4) a control of distilled water. Trials were recorded and consisted of a 5 minute pre-exposure period and a 5 minute post-exposure period. Time spent dashing, time spent motionless, and number of fish moving were recorded. To test learning ability, fish were exposed to stimulus two after initial exposure to stimulus one. If June Sucker exhibited a fright response in reaction to stimulus two, we assumed June Sucker has learned to associate Largemouth Bass odor with predation threat.

Results/Conclusions

June Sucker displayed a fright response to stimuli one and three, but showed no innate fear of stimulus two. A fright response was elicited from exposure to stimulus two after previous exposure to stimulus one. These results suggest that June Sucker produce and detect a chemical alarm cue, can recognize this alarm cue in the diet of a predator, and can learn to recognize predator odors as dangerous.