The effects of different dietary levels of organic and mineral selenium on intestinal morphology and histopathological changes of liver tissue in rainbow trout (Oncorhynchus mykiss) fry

The aim of this study was to evaluate the effect of different levels of organic and mineral sources of selenium on the intestinal morphology and also histologically changes in liver tissues of juvenile rainbow trout for 60 days. For this purpose, 1080 healthy fry fish (50±2.8 g average body weight) were randomly divided into 3 groups, including organic selenium (0.15, 0.30, 0.45, 0.60 mg. kg-1), mineral selenium (0.15, 0.30, 0.45, 0.60 mg. kg-1) and a control group with triplicates. At the end of trial, 3 fish were caught in each treatment. After anesthesia, the fish were autopsied. The liver and intestine of fishes were removed and histologically studied by standard tissue procedures. Finally, prepared tissues were evaluated by optical microscopy. The microscopic and morphometric results indicated a significant improvement in the morphological changes of the intestinal tissue including the auxesis of absorption area, length and diameter of villi and abate of depth of villi crypt in treatment containing 0.45 mg. kg-1 organic selenium of diet compared with other treatments and control group (p<0.05). Also, the least histopathological changes of liver tissue in the treatment containing 0.45 mg. kg-1 organic selenium in diet and the most extensive lesions wereobserved in both the control group and higher levels of dietary mineral selenium. It seems that, the treatment containing 0.45 mg. kg-1 organic selenium in diet were identified as the best supplement for improving of the intestinal tract and decrease in possible histopathological side effects in rainbow trout.