Histopathological alterations of juvenile green (Acipenser medirostris) and white sturgeon (Acipenser transmontanus) exposed to graded levels of dietary methylmercury.

Triplicate groups of juvenile green and white sturgeon (average weight of 30 ± 2 g) were exposed to one of four concentrations of dietary methylmercury (MeHg; 0, 25, 50, and 100 mg MeHg/kg diet) for 8 weeks to determine and compare the sensitivity of the two sturgeon species from a histopathological perspective. After 4- and 8-week exposure, histological changes were examined in the kidney, liver, gill, skeletal muscle, and heart muscle of both species using light microscopy. Marked abnormalities were observed in the kidney and liver of both sturgeon species after each exposure period; the abnormalities showed progressive histological alterations in severity with increasing doses and duration of exposure. Renal lesions included tubular epithelium degeneration and necrosis, renal corpuscular disintegration, and interstitial tissue degeneration. The changes observed in the livers of both sturgeon species were glycogen depletion and vacuolar degeneration. In the gill and skeletal and heart muscle of green and white sturgeon fed MeHg-added diets, mild histological changes were observed but did not show pronounced difference between the two species. Although the lowest observed effect concentration in both species was the 25 mg MeHg/kg diet, the histological changes in the kidney and liver were more pronounced at all treatments groups of green sturgeon than those of white sturgeon. The current results on structural changes of kidney and liver (i.e., more severe glycogen depletion and tubular epithelium degeneration in green sturgeon) confirmed our previous results, in that green sturgeon exhibited a higher mortality, lower growth rate, and lower protein, lipid, and energy contents in their whole body than white sturgeon under the same MeHg exposures.