Susceptibility of rainbow trout (Salmo gairdneri) to enteric redmouth disease following exposure to technical PCBs and waste transformer oil containing PCBs
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Rainbow trout fry Salmo gairdneri were exposed to estimated concentrations of 0, 0.38, 0.75, 1.5, 3.0, and 6.0 pg/liter total PCBs for 90 days, and then held in fresh water for another 60 days. Two sources of PCBs were used: (1) waste transformer oil containing various hydrocarbons plus a 1:2 ratio of the PCBs Aroclors 1254 and 1260, and (2) pure technical PCBs of the same Aroclor ratio as in the transformer oil. Survival of fish in transformer oil was much less than that of fish in technical PCBs at 90 days. Growth was severely reduced within 30 days in the transformer oil, whereas technical PCBs, at the highest concentration, did not affect growth until 90 days. Vertebral integrity was not affected by exposure to technical PCBs. However, vertebral collagen, calcium, and phosphorus increased in fish exposed to transformer oil. Abnormal swimming behavior of fish exposed to transformer oil was attributed to reduced percent volume of the swimbladder and increased sinking factor and density, which consequently caused fish to remain on the bottom of aquaria. Exposure to transformer oil decreased hematocrit and increased serum cortisol to twice that of controls and of fish exposed to technical PCBs. However, exposure to both technical PCBs and transformer oil increased disease resistance of fish as measured by flush disease challenges (bacteria poured into aquaria water) to Yersinia ruckeri on days 45, 60, and 90 of contaminant exposure. When the disease organism was injected intraperitoneally, fish exposed to transformer oil died earlier than control fish or fish exposed to technical PCBs. Since neither of the PCB mixtures was bacteriostatic or bactericidal to Y. ruckeri, contaminant-induced mucification of the gills may have prevented infection in the flush disease challenges. Although exposure concentrations were essentially identical for both PCB sources, fish exposed to transformer oil had considerably lower PCB residues than fish exposed to technical PCBs, an anomaly attributed to the effects of hydrocarbons in the transformer oil on solubility and bioconcentration of PCBs. Petroleum hydrocarbons additionally caused severe fin erosion in trout exposed to transformer oil. Fins of fish exposed to technical PCBs were not eroded.
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