Effects Of Selenium Yeast And Tea Polyphenols On Growth Performance, Antioxidant Activity And Stress Resistance Of Wuchang Bream

Selenium yeast(SY) and tea polyphenols(TP) belong to high-quality natural antioxidants. As an organic selenium source, SY has the effect of both antioxidant and immune-enhancer. Tea polyphenols(TP) is a term for polyphenols in tea, which is helpful to free radicals scavenging, anti-bacterial and anti-inflammatory actions, immunomodulatory effects and so on. In the present study, a two-factorial and three-level experiment was designed to evaluate the effects of dietary SY and TP on growth performance, nutritional composition of muscle, the activities of antioxidant enzymes as well as the transcriptional levels of antioxidant enzyme genes and growth-related genes in the liver and brain of Wuchang bream, Megalobrama amblycephal. Totally nine semi-purified diets were formulated to provide graded levels of Se(0, 0.25, 0.50 mg/Kg) and TP(0, 50, 100 mg/Kg). After 8 weeks of feeding trial, the possible molecular mechanisms of SY and TP on growth and antioxidant performance were analysed and he optimum addition of SY and TP were chosen preliminarily. An acute nitrite stress experiment was futher conducted to evaluate the effects of SY and TP on serum stress hormones, the activity and gene expression of antioxidant enzymes and liver histology under nitrite acute stress. The results showed as follows,1. Dietary SY significantly enhanced selenium contents in the muscle and liver(P<0.01), whereas there was no significant effect of dietary TP on selenium deposition(P>0.05), and the interplay of dietary SY and TP on selenium deposition was significant in liver(P<0.05). Both dietary SY and TP significantly enhanced the activities of glutathione peroxidase(GPX), superoxide dismutase(SOD), catalase(CAT) by upregulating the expression of these antioxidant enzyme gene. The difference is that SY upregulated m RNA expression of Ma GPx1 and Ma Cu/Zn-SOD significantly(P<0.05), whereas TP raised Ma CAT.(3) The combination of SY and TP has synergistic antioxidant effects by upregulating Ma GPx1 gene expression significantly and promoting the transcription of Ma Cu/Zn-SOD and Ma CAT. As a result, fish fed the combination diets with SY and TP had higher hepatic total antioxidant capacity(T-AOC) and lower content of Malondialdehyde(MDA) than fish in the other dietary groups(P<0.05). In conclusion, a basal diet supplemented with 0.50 mg/kg SY and 50 mg/kg TP could improve the hepatic antioxidant enzymes activities and reduce MDA to help keep better antioxidant status in juvenile Wuchang bream.2. Dietary SY and TP significantly enhanced the growth performance by upregulating the m RNA expression of growth related genes in the hypothalamus-pituitary-growth axis. The difference is that SY mainly upregulated the m RNA expression of Ma GH and Ma IGF-â… significantly(P<0.05), whereas TP enhanced the transcription of Ma GHR2 and decreased the m RNA level of Ma IGF-â… significantly(P<0.05). Consequently, dietary SY significantly enhanced the contents of GH and IGF-â… in the serum, whereas TP decreased serum IGF-â… levels significantly(P<0.05). No significant interaction effect of dietary SY and TP on serum GH and IGF-â… was observed in juvenile Wuchang bream(P>0.05). Both dietary SY and TP significantly enhanced the crude protein content in the muscle(P<0.05). And there was no significant interaction effects of dietary SY and TP on the content of the crude protein in the muscle(P>0.05). Both dietary SY and TP could improve the ability to resist Aeromonas hydrophila(P<0.05). And there was an interaction effect of SY and TP on the ability to resist Aeromonas hydrophila. In brief, the basal diet supplemented with 0.50 mg/kg of SY and 50 mg/kg of TP could help keep better growth performance and disease resistance in juvenile Wuchang bream.3. Under nitrite stress, the basal diet supplemented with 0.50 mg/kg of SY and 50 mg/kg of TP and its combination induced a increase in both the antioxidant enzyme activities and gene expression levels to some extent, which could alleviate oxidative damage caused by nitrite stress. Morever, SY mainly improved the activity and gene transtrion of GPX and TP increased SOD, their combination significantly upregulated GPX(P<0.05). In light of the above, it was concluded that a basal diet supplemented with 0.50 mg/kg of SY or the combination of 0.50 mg/kg of SY and 50 mg/kg of TP could enhance growth performance while alleviate nitrite stress by improving antioxidant capacity in Wuchang bream.