PCBs can diminish the influence of temperature on thyroid indices in rainbow trout (Oncorhynchus mykiss)

The influence of PCBs on the thyroid status of rainbow trout was assessed at various temperatures to identify if PCB mixtures, as well OH-PCBs produced via biotransformation of parent PCBs, can illicit thyroid effects in fish. Juvenile rainbow trout (Oncorhynchus mykiss) held at 8, 12 or 16°C were exposed to dietary concentrations of an environmentally relevant mixture of PCBs for 30 days followed by a depuration phase. Two additional treatments at 12°C included higher concentrations of PCBs (congeners 77, 126 and 169) known to induce CYP1A in fish (referred to as CYP1A treatment) and PCBs (congeners 87, 99, 101, 153, 180, 183 and 194) known to induce CYP2B in mammals (referred to as CYP2 treatment), to assess the influence of more biologically relevant PCB congeners on thyroid indices in fish. Growth rate and liver somatic index varied with water temperature (p0.05) and mortality was low in all treatments. Changes in some measures of thyroid status were apparent in PCB-exposed fish held in the 12 and 16°C treatments while other measures showed no change in any treatment. The natural inverse relationship between thyroid epithelial cell height (TECH) and temperature, was diminished after 30 days of exposure to PCBs as the epithelial cell height in PCB-exposed fish was significantly augmented in the 12 and 16°C treatments compared to controls at these temperatures (p