PROLONGED SWIMMING, RECOVERY AND REPEAT SWIMMING PERFORMANCE OF MATURE SOCKEYE-SALMON ONCORHYNCHUS-NERKA EXPOSED TO MODERATE HYPOXIA AND PENTACHLOROPHENOL

Mature, wild sockeye salmon (Oncorhynchus nerka) demonstrated their re markable stamina and recovery abilities by performing three consecutiv e critical swimming speed tests with only a 45 min interval for recove ry between subsequent tests. Although the repeated swimming challenges were performed without a full recovery, normoxic fish swam just as we ll on the second swim, and the majority of fish swam only marginally m ore poorly on the third swim, In addition, metabolic loading in these fish, as measured by the rate of oxygen consumption, ventilation rate and plasma lactate levels during recovery, did not appear to be cumula tive with successive swims. Fish, however, did not recover as well aft er a similar level of initial swimming performance under moderately hy poxic conditions (water P-O2>100 mmHg; 1 mmHg=0.1333 kPa). Four out of the five fish did not swim again and their high plasma lactate levels indicated a greater anaerobic effort, In another group of fish, metab olic loading (elevated control rates of oxygen consumption) was induce d with an overnight sublethal exposure to pentachlorophenol, but these fish swam as well as normoxic fish on the first swim, and five of the six fish swam for a third time at a marginally lower critical swimmin g speed. In contrast to expectations, pentachlorophenol pretreatment a nd moderate hypoxia were not additive in their effects. Instead, the e ffects resembled those of pentachlorophenol pretreatment alone, The re sults are discussed in terms of what aspects of fatigue might impair t he repeat swimming performance of sockeye salmon.