Biochemical and histological responses in rainbow trout (Oncorhynchus mykiss) exposed to 2,3,4,7,8-pentachlorodibenzofuran

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Abstract
Rainbow tout were given an intraperitoneal injection of corn oil containing 0 or 8.8 nmol (3 μg) [14C]2,3,4,7,8-pentachlorodibenzofuran (P5CDF)/kg and were then held on a light cycle that induced spawning 10 months later. At 5- to 6-week intervals, blood samples were collected to monitor plasma levels of 17β-estradiol (E2), testosterone (T), thyroxine (T4), 3,5,3′-triiodo-L-thyronine (T3), and calcium; packed cell volume (PCV); and differential blood cell counts. Fish were sacrificed after spawning to examine tissue P5CDF concentration, liver ethoxyresorufin-O-deethylase (EROD), liver vitamins (retinoids and tocopherol), 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 from contaminated areas. Highest P5CDF concentrations occurred in gut and 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 repeated blood sampling but differential blood cell counts showed adaptive responses to blood removal. The P5CDF exposure caused transient reductions 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.

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