Physiological impact of acute molybdenum exposure in juvenile kokanee salmon ( Oncorhynchus nerka)

Abstract

A series of experiments were conducted to determine the physiological impact of acute sublethal molybdenum exposure to juvenile kokanee salmon ( Oncorhynchus nerka Kennerlyi). Molybdenum was found to be relatively non-toxic to kokanee as the 96 h LC 50 was greater than 2000 mg Mo l −1. Exposure to either 25 or 250 mg Mo .l −1 for 7 days was found to stimulate a significant 1.6- to 1.7-fold increase in ventilation which was later characterized to be dose-dependent between 5 and 250 mg Mo l −1. Acute sublethal molybdenum exposure was found to have little or no impact on kokanee oxygen consumption at rest or immediately following a bout of forced activity or on physiological indicators of stress such as plasma lactate, sodium and cortisol. Despite these findings, prior exposure to 25 or 250 mg Mo l −1 resulted in post-exercise loss of equilibrium and exercise-induced delayed mortality that were not observed in controls. Molybdenum accumulation in gill and liver of kokanee was also characterized. The findings of this study suggest that despite the non-toxic nature of molybdenum, acute sublethal exposure to this metal has physiological consequences to those fish exposed even for only a brief period. Further studies are needed to more fully elucidate the metabolism and mode of action of this metal in fish.