PHYSIOLOGICAL-RESPONSES TO CHALLENGE TESTS IN 6 STOCKS OF COHO SALMON (ONCORHYNCHUS-KISUTCH)

Coho salmon (Oncorhy, chus kisutch) from six hatcheries were reared in a common facility and then subjected to six different challenge tests. Results indicated that there are differences in the response to stressful challenges among stocks of coho salmon. The challenge tests were exposure to salt water (30 parts per thousand), high pH (9.4 and 10.0), low pH (3.55, 3.65, 3.75, and 4.1), thermal increase (1-degrees-C.h-1), disease (bacterial kidney disease), and handling (30-s netting and emersion). The measured responses were changes in plasma sodium and chloride ion concentrations for the saline and pH challenges, critical thermal maximum in the thermal tolerance test, mortalities in the disease challenge, and plasma glucose alterations in the handling challenge. The Chehalis River stock was most successful in tolerating salt water but showed the largest plasma ion decrease in acidic waters. The stock from Eagle River had the lowest plasma glucose increase during handling challenges. In the disease challenge the Tenderfoot Creek and Eagle River stocks had high mortalities but the Capilano River stock had the lowest mortality. No stock differences were found during thermal tolerance and high pH challenges. An assessment of overall stock performance across challenges showed that each stock had a unique response profile.