Effects of an Experimental Cortisol Challenge on the Behaviour of Wild Radio-Tagged Creek Chub in Late Fall

Little is known about how wild fish respond to experimental stressors, such as the use of cortisol implants, despite the fact that these approaches have the potential to yield information on the ecology of stress in natural systems.  In this study, the consequences of stress on the spatial ecology of wild creek chub (Semotilus atromaculatus) were studied by using a single intra-peritoneal injection of cortisol, suspended in coconut oil, to experimentally raise plasma cortisol levels within fish.  Radio-telemetry was used to study the movements and habitat use of 11 cortisol-treated and 12 control fish (total size range of 140- 206 mm) in a low gradient suburban tributary of the Rideau River in Ottawa, Canada.  Over a 28 day period in the late fall, individual creek chub were positioned every second day, via manual tracking, to assess large-scale movements.  On two occasions a subset of the tagged creek chub were positioned 4 times throughout the day to assess fine-scale movements.  This study represents one of the first efforts to use experimental cortisol implants outside of a laboratory environment and yields insight into how wild animals respond to additional challenges.