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UBC Theses and Dissertations

The influence of sub-lethal zinc exposure on olfaction of alarm cues and associated alarm behaviours in juvenile coho salmon Smith, Anna E.


Urban streams are under constant assault from pollutants, including highly damaging heavy metals. Zinc is a common and nearly ubiquitous contaminant in urban streams and water bodies with a myriad of sources including mining, agriculture, commercial industry, and stormwater runoff. At high levels, zinc is known to cause physical damage and death to olfactory cells in fish, resulting in a loss of smell. This is highly concerning, as fish use their sense of smell for foraging, communication, migration, mating, and defence. This is particularly true for salmonid species like coho, that lack other methods of predator defence. While most urban streams do not contain high levels of zinc contamination, zinc is often present at lower concentrations. The influence of zinc on olfaction at low levels is not well understood and could have significant impacts on survival. In the present study, juvenile coho were exposed to environmentally relevant levels of zinc (30 - 120 µg/L for 3 hours) and were then challenged with a con-specific chemical alarm cue, which was intended to reflect a nearby predation event. Coho that were not exposed to zinc immediately reduced their activity and demonstrated classic anti-predator behaviours such as sinking, shoaling, and freezing in place. The coho exposed to any of the three levels of zinc failed to react to the alarm cue and showed little to no expected alarm behaviours. This suggests that the current acceptable limit of 33 µg/L of zinc outlined in the BC water quality guidelines is not protective for coho juveniles. The inhibition of successful olfaction and reaction to an alarm cue shows that zinc exposed fish are compromised by low level zinc contamination and fail to respond to their chemosensory environment appropriately. This could have large impacts on predator avoidance and, ultimately, survival through the freshwater phase.

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