Effects of Dietary β‐1,3‐Glucan on Expression of Immune‐related Genes of Litopenaeus vannamei Exposed to Nitrite‐N

The effects of β‐1,3‐glucan on growth and expression of immune‐related genes in muscle were evaluated by a 84‐d feeding trial in white shrimp, Litopenaeus vannamei, fed diets containing 0, 250, 500, and 1000 mg/kg β‐1,3‐glucan, respectively. After the feeding trial, the shrimp were exposed to nitrite‐N (20 mg/L) for 120 h. The transcript abundance of hemocyanin, LPS/b‐glucan binding protein (LGBP), Penaeidin‐3, prophenoloxidase (proPO), Serine proteinase, and superoxide dismutase (SOD) was quantified by real‐time PCR. The results showed that during 84‐d feeding trial, 250 mg/kg β‐1,3‐glucan group showed significantly higher weight gain rate than control. There were no significant differences of survival rate between groups, but survival rate correlated inversely with dietary β‐1,3‐glucan levels ( r 2 = 0.96). Significantly upregulated LGBP were observed in 500 mg/kg β‐1,3‐glucan group compared to control. After 120 h nitrite stress, the expression level of hemocyanin, LGBP, proPO, Serine proteinase, and SOD in shrimp fed with 500 or 1000 mg/kg β‐1,3‐glucan were significantly higher than those in shrimp fed with other diets. Together, in this 84‐d feeding trial, 250 mg/kg β‐1,3‐glucan improved growth, whereas 500 mg/kg β‐1,3‐glucan preferentially improved nitrite resistance, probably through upregulating expression of immune‐related genes.