The effects of acute waterborne exposure to sub-lethal concentrations of molybdenum on the stress response in rainbow trout (Oncorhynchus mykiss)

• Main Author: Ricketts, Chelsea Dawn
• Language: English
• Published: University of British Columbia 2009
• Online Access: http://hdl.handle.net/2429/9311

Molybdenum (Mo) is an essential metal that is increasing in popular demand as a valuable natural resource. Exploration activity in British Columbia, which hosts over 1350 molybdenum-bearing deposits, has exploded and there are over a handful of projects that have potential to begin operations. The metal’s rapidly growing production and use represents a potential for increased release and distribution into the aquatic environment, especially in British Columbia. Although molybdenum is considered relatively non-toxic to fish, toxicity data are severely lacking and nothing is known about the effect of molybdenum on the stress response. To determine if molybdenum acts as a stressor, fingerling and juvenile rainbow trout(Oncorhynchus mykiss) were exposed to waterborne molybdenum (0, 2, 20, or 1000 mg/L) and components of the physiological (plasma cortisol, blood glucose, and hematocrit) and cellular [heat shock protein (HSP) 72, HSP73, HSP90, and metallothionein (MT)] stress responses were measured prior to initiation of exposure and at 8, 24, and 96 h during exposure. An ELISA revealed no alterations in plasma cortisol from any molybdenum treatment. Similarly, no changes in blood glucose, measured using a hand-held meter, or hematocrit that could be attributed to the stressor were found. Western blot analyses were used to measure the accumulation of HSPs in the liver and/or gills of fingerlings and in the liver, gills, heart, and erythrocytes of juveniles and MT in the liver of fingerlings and in the liver and gills of juveniles. HSP72 was not induced nor were there changes in HSP73, HSP90, and MT levels in any of the tissues relative to controls. Both fingerling and juvenile fish responded with similar lack of apparent sensitivity to molybdenum exposure. These experiments demonstrate, for the first time, that exposure to waterborne molybdenum of up to 1000 mg/L did not activate a physiological or cellular stress response in fish. These findings are consistent with previous studies suggesting that fish are resistant to molybdenum. Information from this study suggests that molybdenum water quality guidelines for the protection of aquatic life are highly protective of rainbow trout.