دانلود رایگان مقاله پاسخ رفتاری ماهی آزاد اقیانوس آرام به نشانه اختلال شیمیایی

Abstract

Many fish that are exposed to a threat release disturbance cues, which are chemicals that alert conspecifics to the presence of the threat. The release of disturbance cues has been well demonstrated in various species of laboratory-reared fish. Migratory fish species often exhibit increased cortisol levels and are exposed to numerous stressors during their migrations, which could trigger the release of disturbance cues. We tested the responses of wild migrating sockeye salmon (Oncorhynchus nerka) and pink salmon (O. gorbuscha) to the odours of disturbed and undisturbed conspecifics to determine whether these fish release disturbance cues following exposure to a simulated stressor. Furthermore, we tested the responses of sockeye salmon to water-borne cortisol, following evidence from past studies that this chemical is excreted through the gills of stressed fish, and speculation that endogenous correlates of stress might function as disturbance cues. We found that sockeye salmon avoid the odour of disturbed conspecifics, whereas pink salmon do not. Avoidance occurred in both female and male sockeye salmon, and was associated with an increase in plasma cortisol levels in females, but not in males. We also found no behavioural response to water-borne cortisol, which suggests this chemical does not act as an exogenous disturbance cue in sockeye salmon. Avoidance of disturbed conspecifics could limit exposure to risks during the sockeye salmon spawning migration, but could also delay the rate of migration and thereby accrue reproductive costs.

4. Discussion

The responses of sockeye salmon to the odour of the handled conspecifics suggest disturbance cues were released following the handling event. Sockeye salmon in the Y-maze avoided the odour of disturbed conspecifics, spending less total time and a lower proportion of time in that arm, and entering it less frequently. When lethally percussed sockeye salmon were used as a source odour (as controls to the disturbed fish), test subjects did not display avoidance or attraction behaviours, further confirming that the handled fish did indeed emit disturbance cues. Our finding suggests that disturbance cues can be released by migrating adult sockeye salmon Similar responses to the odour of handled conspecifics have been found in other species of fish that were not undergoing migrations.