The Effect of Food Deprivation on the Cortisol Response to Crowding in Juvenile Steelhead

Abstract

Routine salmonid hatchery procedures include food deprivation, handling, and crowding of fish before sorting, transporting, or stocking. Although several studies have examined the effects of food deprivation or husbandry stressors on salmonid physiology, few have examined the effects of food deprivation and standard hatchery procedures, such as handling and crowding. The objective of this study was to determine whether food deprivation of juvenile steelhead (anadromous rainbow trout Oncorhynchus mykiss) affects the cortisol response to stress from low-water crowding. Plasma cortisol levels of fish held in circular fiberglass tanks at 8°C under normal daily feeding conditions were compared with levels in fish subjected to 3 d of food deprivation; both groups were held at 3.8 kg/m³ (control density). Additionally, these groups were compared with fed and food-deprived fish held at a density of 12.8 kg/m³ for 3 h (low-water crowding stressor). There was a significant increase in plasma cortisol levels of fish subjected to low-water crowding (129.9 ng/mL) relative to fish held at the control density (14.7 ng/mL), regardless of previous feeding treatment. However, for fish at a given density (control or crowded), there was no difference in cortisol levels between fed and food-deprived groups. We conclude that depriving juvenile steelhead of food does not significantly alter their cortisol response to low-water crowding. Consequently, the standard hatchery practice of withholding food before performing stressful husbandry procedures does not appear to cause additional stress or exacerbate physiological responses typically observed in steelhead after they are subjected to physical stressors.