BIOCHEMICAL AND HISTOLOGICAL RESPONSES IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) EXPOSED TO 2,3,4,7,8-PENTACHLORODIBENZOFURAN

Rainbow trout were given an intraperitoneal injection of corn oil cont aining 0 or 8.8 nmol (3 mu g) [C-14]2,3,4,7,8-pentachlorodibenzofuran (P5CDF)/kg and were then held on a light cycle that induced spawning 1 0 months later. At 5- to 6-week intervals, blood samples were collecte d to monitor plasma levels of 17 beta-estradiol (E-2), testosterone (T ), thyroxine (T-4), 3.5,3'-triiodo-L-thyronine (T-3), and calcium: pac ked cell volume (PCV); and differential blood cell counts. Fish were s acrificed after spawning to examine tissue P5CDF concentration, liver ethoxyresorufin-O-deethylase (EROD), liver vitamins (retinoids and toc opherol), histology (liver, thyroid), and growth parameters. The P5CDF injections produced tissue 2,3,7,8-tetrachlorodibenzo-p dioxin toxic equivalent concentrations comparable to those reported in salmonids fr om contaminated areas. Highest P5CDF concentrations occurred in gut an d liver, but muscle accounted for the greatest proportion of the dose. Plasma hormone and calcium concentrations followed predicted seasonal patterns in both control and exposed fish. PCV was unchanged by repea ted blood sampling but differential blood cell counts showed adaptive responses to blood removal. The P5CDF exposure caused transient reduct ions in circulating lymphocytes and elevated EROD. Additionally, P5CDF increased liver size and depleted retinoid stores in male fish. Liver histology, somatic growth, and gonadal development were unaltered by P5CDF during the first reproductive cycle after exposure.