Morphologic lesions and acute toxicity in rainbow trout(Salmo Gairdneri)treated with 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin

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Abstract
To determine effects of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) on growth, mortality, and morphologic lesions in rainbow trout, juvenile Shasta or Wytheville strain fish, obtained from 4 hatcheries, were administered graded single doses of TCDD, 0.1–125 μg/kg, ip. TCDD doses of 25 and 125 μg/kg caused 85% lethality 2–4 wk after treatment. At these high doses, death occurred before body weight loss could be detected. A lower dose of 5 μg/kg caused decreased growth and cumulative mortality of 20% after 11 wk. Stress associated with netting and weighing the fish at weekly intervals significantly shortened the delay period prior to TCDD‐induced lethality. Gross and microscopic lesions were evident in rainbow trout treated with 10 μg TCDD/kg, but not in fish treated with 1 or 0.1 μg/kg. Morphologic lesions occurred consistently in epithelial and lymphomyeloid tissues of TCDD‐treated fish. Lymphomyeloid lesions included thymic involution, splenic lymphoid depletion, and hypocellularity of hematopoietic tissues in the head kidney and trunk kidney. In association with decreased hematopoiesis, peripheral leukopenia and thrombocytopenia occurred in Shasta strain yearling trout treated with 1 μg/kg or more TCDD. Regarding epithelial lesions, all 4 hatchery strains treated with 10 μg/kg or more TCDD showed multifocal necrosis of gastric cardiac glandular mucosa, 3 of 4 hatchery strains showed vacuolar inclusions in exocrine pancreatic cells, and 2 of 4 hatchery strains showed fin necrosis. The severity and character of lesions in the liver and gastric mucosa varied mark‐

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