TOXICITY OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN TO EARLY-LIFE STAGE BROOK TROUT (SALVELINUS-FONTINALIS) FOLLOWING PARENTAL DIETARY EXPOSURE

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to the earl y life stages of F-1 generation brook trout (Salvelinus fontinalis) wa s determined, when dosed by maternal transfer. Effects were compared a cross six treatments, including a control. The experimental groups, ba sed on TCDD concentrations in freshly spawned eggs (control, 41, 84, 1 56, 285, and 517 pg TCDD per gram egg [wet weight]), were established by treating 1.5-year-old brook trout with TCDD-dosed food throughout t he period beginning with final gonadal maturation and continuing until just prior to spawning. Measurement endpoints assessed at various tim es throughout the study, included (1) TCDD and lipid concentrations in ovaries, eggs, alevins, and juvenile fish, (2) mortality, (3) fertili ty indices, (4) growth, (5) juvenile sex ratios, (6) pathology, and (7 ) cytochrome P4501A1 mRNA (CYPIA1) levels in embryos. The cumulative l ethality dose response was determined just prior to hatch, at swim-up, and at the end of the study. The concentration in eggs causing 50% mo rtality (LC(egg)50) at swim-up and at the end of the study were 138 an d 127 pg TCDD per gram egg, respectively. No treatment effects were ob served on fertility, growth, or juvenile sex ratios. Pathologies were observed that have been previously reported in TCDD-exposed salmonid e mbryos, including edema in free embryos from all TCDD-exposed treatmen t groups at hatch. At the end of the test, juvenile fish from all trea tments exhibited an increased prevalence of exophthalmia compared to t he controls. The EC(egg)50 for this effect was 117 pg TCDD per gram eg g. Histological analysis of the end-of-test juveniles, in gonad, nerve , vertebrae, neuromasts, liver, kidney, gut, gas bladder, skin, and bl ood vessels, did not indicate any significant pathology below the LC(e gg)50. P4501A1 mRNA levels in whole 91-d postspawn free embryos from t he 84 pg TCDD per gram egg treatment were 2.8 times higher compared wi th control or 41-pg TCDD per gram egg treatments. Results from this st udy were consistent with other published results of TCDD effects on sa lmonids, in which the exposures occurred after fertilization.