Effect of dietary β-1,3-glucan on the immune response of Litopenaeus vannamei exposed to nitrite-N

β-1,3-Glucan with 1.0 g kg−1 was supplemented to a basal diet [control (C)] with different feeding schedules: permanently β-1,3-glucan diet (BG) and 14 days BG–14 days control diet (C + BG). Growth and immunological responses [respiratory burst (RB), superoxide dismutase (SOD), catalase (CAT), lysozyme and total protein] in haemolymph, hepatopancreas and muscle of Litopenaeus vannamei were recorded after 84-day feeding and exposure to nitrite-N (20 mg L−1) for 120 h. β-1,3-Glucan administration did not affect growth performance. However, as compared with control, elevated CAT and lysozyme activities were seen in haemolymph of both BG groups, while significantly higher activities of SOD, lysozyme and RB in hepatopancreas, and higher activities of CAT and lysozyme in muscle were only seen in C + BG group. After nitrite-N stress, significantly higher haemolymph protein, and hepatopancreas activities of lysozyme and RB were observed in both BG groups, but significantly higher activities of haemolymph SOD was only seen in C + BG group. The mortality in groups BG and C + BG was significantly lower than that in group C, but C + BG group showed a trend of higher nitrite-N resistance compared with BG group. Considering dietary cost and immunostimulatory effects, the feeding schedule with 14 days BG–14 days control diet is more recommended.