Influence of dietary exposure to polychlorinated biphenyl 126 and nutritional state on stress response in tilapia (Oreochromis mossambicus) and rainbow trout (Oncorhynchus mykiss)

Abstract

AbstractPolychlorinated biphenyls (PCBs) are highly toxic pollutantss ructurally resemblings eroidhormones, interfering with synthesis and action of gonadal and adrenocortical steroids, and impairing the cortisol‐ and adrenocorticotropic hormone (ACTH)‐mediated stress response in fish. In this study on tilapia and rainbow trout, we analyzed the influence of dietary PCB on the response to a nontoxic stressor (confinement) as well as the influence of starvation following the PCB exposure on this response. Fish, in duplicate tanks, were fed diets containing 25 μg (low) or 2, 500 μg (high) of PCB 126 per kilogram of food per day for five days. After the exposure, fish from one control, low‐PCB, and high‐PCB diet tank were sampled directly or after confinement. Fish in the second group of these tanks were starved for three weeks to allow mobilization of stored PCBs and then sampled directly or after confinement. In fish sampled directly after the PCB exposure, basal hormone and glucose levels were not affected. After confinement, plasma cortisol rose to the same high levels in all groups. Adrenocorticotropic hormone levels in confined fish (both species) increased with increasing PCB load. Only fish fed the high‐PCB diet showed impaired hyperglycemia. After starvation, only basal plasma glucose levels were lower in fish fed the high‐PCB diet. All other parameters were unaffected in resting fish. Confining PCB‐fed and starved fish resulted in elevated plasma hormone levels that were lower than in confined, starved control fish. Plasma glucose levels in starved and unstarved fish were similar. Morphometric analysis of head kidney interrenal cells revealed only subtle, species‐specific changes. We conclude that PCB 126 has disruptive actions on the hormonal regulation of the stress response. Starving PCB‐fed fish did not further impair the hyperglycemic response to confinement but did affect the ACTH‐ and cortisol‐mediated responses to confinement. A poor nutritional status is concluded to enhance the negative effects of PCBs on the stress responsiveness of fish.