CYP1A induction and blue sac disease in early developmental stages of rainbow trout (Oncorhynchus mykiss) exposed to retene

Early life stages of rainbow trout were exposed to different regimes of water-borne retene (7-isopropyl-1-methylphenanthrene) to determine if there is an ontogenic stage particularly sensitive to retene toxicity, and if cytochrome P-4501A (CYP1A) induction is a forerunner to blue sac disease (BSD), the syndrome of toxicity. CYP1A protein concentrations, measured by immunohistochemistry, were first detected during organogenesis, when organ and enzyme systems are first being developed, and steadily increased until swim-up. The prevalence of signs of BSD rose 1 wk following a marked increase in CYP1A activity after hatch, suggesting that CYP1A induction is related to BSD. The larva/stage was the most sensitive to retene toxicity, based on CYP1A induction and a high prevalence of BSD. The most common signs of BSD were hemorrhaging, yolk-sac edema, and mortality, but hemorrhaging was the first and most frequently observed response. Tissue concentrations of retene were elevated just after fertilization, but decreased steadily as fish developed to the swim-up stage, most likely due to the establishment of more efficient metabolic and excretory systems in later stages of development.