| Selenium(Se)is an essential trace element to maintain the normal growth of animals.At present,there have been extensive studies on the optimal level of Se in aquatic animal feed.However,the physiological regulation mechanism of Se on aquatic products is still unclear.To explore the effects of dietary Se levels,Se sources and the underlying mechanism of anti-stress regulation on the growth and health of Litopenaeus vannamei,biochemistry,physiology,RNA-seq and gut microbiota were used.The main content of the paper is as follows:1 The effect of different feed selenium levels on the growth,physiological and biochemical and molecular responses of L.vannameiSodium selenite was added to basal diet formulations at 0,0.2,0.4,and 0.8 mg/kg,with final Se concentrations of 0.13,0.20,0.45,and 0.81 mg/kg,respectively.Shrimp were fed the experimental diets for 8 weeks.Shrimp fed the 0.45 and 0.81 mg/kg Se diets(P<0.05)showed the highest weight gain,shrimp fed the 0.13 mg/kg Se diet had the highest hepatosomatic index(P<0.05),and the endoplasmic reticulum stress related genes were down-regulated(P<0.05)in shrimp fed the 0.45 mg/kg Se diet.Antioxidant enzyme activity(SOD,CAT,and GPx)was enhanced with the increase in the Se level.The transcriptome results showed that glycine,serine,and threonine metabolism,the pentose phosphate pathway,and ascorbate and aldarate metabolism were enriched in shrimp fed the 0.45 mg/kg Se diet,while focal adhesions,gap junctions,tight junctions,and adhesion junctions were found in shrimp fed the 0.13 and 0.81 mg/kg Se diets.Co-expression analysis showed that genes PINK1 and Innexin(among others),were involved in the influence of Se levels on shrimp.Our results suggested that Se supplementation improved the growth and antioxidant capacity of L.vannamei by promoting the biosynthesis of glutathione and enhancing the activity of antioxidant enzymes.However,high levels of dietary Se can cause endoplasmic reticulum stress and hepatopancreas tissue damage.2 The effects of different selenium sources in feed on the growth,antioxidation,gut microbiota and molecular response of L.vannameiJuvenile shrimp(1.60±0.14 g)were fed with sodium selenite,L-selenomethionine,selenium yeast and Se nanoparticle at 0.40 mg/kg Se supplementation.After 8-week trial,the L-selenomethionine and selenium yeast significantly increased weight gain(P<0.05),while sodium selenite significantly decreased hepatosomatic index compared with other groups(P<0.05).The L-selenomethionine significantly increased SOD and GPx activity compared with sodium selenite(P<0.05),while it decreased CAT activity and MDA content compared with other groups(P<0.05).In the gut microbiota analysis,Lselenomethionine,selenium yeast and Se nanoparticle affected the abundances of Rubrobacter and Rubritalea,Winogradskyella and Motilimonas,Photobacterium in gut microbiota,respectively.L-selenomethionine kept the composition of the gut microbiota in a more stable state.RNA-seq analysis was used to identified differential expression compared with sodium selenite group."Arachidonic acid metabolism" was both enriched in SeMet and Se yeast groups.A number of amino acid and lipid metabolism-related genes associated with Vibrio,Motilimonas,Photobacterium etc.Overall,these results reveal that organic Se promoted the growth and antioxidant capacity of L.vannamei.and maintained the normal composition and function of the gut microbiota and increased the utilization of nutrients.3.Effects of selenomethionine on growth,antioxidation,hepatopancreas health and resistance to nitrite stress in Litopenaeus vannamei under low salinity stressL-selenomethionine was added to the basic feed to the selenium content to be 0.4,0.8 and 1.6 mg/kg,respectively.Four experimental groups:the selenium level in normal seawater was 0.4 mg/kg feed(seawater control);the selenium level in low-salt environment(3 psu)was 0.4(low salinity control),0.8 mg/kg and 1.6 The feed of mg/kg was mixed to culture L.vannamei for 8 weeks.After the end,it was placed under nitrite(110 mg/kg)stress for 24h.The results showed that the weight gain rate of prawns fed with a selenium level of 0.8 mg/kg under low salinity was significantly higher than that of other low-salt groups(P<0.05),and the ash content was significantly lower than that of the seawater control group(P<0.05).The antioxidant enzyme activity of prawns fed with selenium levels of 0.8 and 1.6 mg/kg under low salinity increased(P<0.05).Transcriptome results showed that compared with the seawater control,the low salinity control was significantly enriched in different expressed genes in metabolic pathways such as glutathione metabolism,fructose and mannose metabolism,retinol metabolism,and oxidative phosphorylation;compared with the selenium level 0.8 mg/kg group low salinity control different expressed genes were significantly enriched in retinol metabolism,steroid hormone biosynthesis,multiple carbohydrate metabolism related pathways(pentose,glucuronic acid conversion,other O-glycan biosynthesis,mucin-type O-glycan The biosynthesis of selenium,etc.);selenium level 1.6 mg/kg group of differential genes compared with low salinity control were significantly enriched in fructose and mannose metabolism,oxidative phosphorylation,glutathione metabolism,steroid hormone biosynthesis,carbohydrate metabolism(biosynthesis of other O-glycans,biosynthesis of mucin-type O-glycans,etc.)and other pathways.Through the above research,it is found that selenium promotes the synthesis of GSH by enhancing the activity of GPx,regulating the PI3K-Akt signaling pathway and the metabolism of glycine and serine,thereby enhancing the antioxidant capacity.Organic selenium(selenomethionine and Se yeast)can better promote the growth and antioxidant capacity of L.vannamei,reduce the relative abundance of potential pathogens,and promote the metabolism of fat and amino acids in the shrimp.It is the most optimal selenium source for L.vannamei.Selenium responds to the negative effects of low salinity stress by regulating the carbohydrate metabolism,antioxidant system and hormone synthesis of L.vannamei. |
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