CONCURRENCE OF P450-1A1 INDUCTION AND TOXIC EFFECTS AFTER ADMINISTRATION OF A LOW-DOSE OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) IN THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Juvenile rainbow trout received a single intraperitoneal injection of 0.006, 0.03, 0.06, 0.30, 0.60 or 3.06 mug 2,3,7,8-tetrachlorodibenzo-P-dioxin (TCDD)/kg body weight and were killed after three, six or twelve weeks. In the twelfth week after treatment of the highest dose, a 20% mortality was observed in the remaining fish of this dose group. Growth inhibition was noted six weeks after the highest dose. The relative liver weight did not show pronounced changes. However, histopathological evaluation revealed inflammation, single cell necrosis and sinusoidal dilatation. Three and six weeks after treatment the relative spleen weight showed an increasing trend, which might be attributed to congestion of erythrocytes. In addition lymphocyte depletion and congestion were observed from dose levels of 0.30 mug/kg. A dose related EROD (7-ethoxyresorufin O-deethylation) activity was observed after three weeks, statistically significant from the controls at dose levels of 0.30 mug/kg or higher. The ED50 for EROD activity was established at 0.79 +/- 0.49 mug TCDD/kg. The total cytochrome P450 content parallels more or less the EROD activity. Thus a concomitant occurrence of toxicological effects and P450 1A1 induction were found at dose levels of 0.30 mug/kg or higher, which classifies the rainbow trout among the more sensitive species for these type of compounds.