Stress Response Associated with Hatchery Conditions in Developing Chum Salmon

To assess the impact of hatchery techniques on the stress response of Chum Salmon, developing fish (eyed-egg to fry stage) were subjected to treatments of formalin, low-medium-high densities and mechanical distress. While in controlled laboratory aquaria, routine hatchery practices were mimicked to replicate algal control (formalin), density differences, and shock and pick or transport (mechanical distress). Formalin, which is routinely used to control algal outbreaks, was administered (1ppt) and compared to control (no formalin) tanks. Mean cortisol levels for the treated eggs immediately increased ~350% (= 323.84±18.16pg/ml versus only = 70.84±5.42pg/ml in the control eggs) and remained elevated for 45 minutes until returning to control treatment levels. Mean cortisol levels differed significantly between the formalin treatment and control at all density levels (high density p=0.038, medium density p=0.028, low density p=0.048). Mortality rates at all densities also varied significantly between formalin treatment and control (high density p=0.010, medium density p=0.029, low density p=0.009).  Shock and pick, as well as transport of salmon fry, was mimicked with mechanical distress and cortisol levels measured to assess stress response. Interestingly, cortisol levels did not increase until mechanical distress continued for 150 minutes whereby cortisol concentrations increased ~1750% above control levels. These results should help identify stress responses during early life stages of chum salmon as well as identify potential sources of anthropogenic stress associated with hatcheries.