Suppression of white feces syndrome in Pacific white shrimp, Litopenaeus vannamei, using hen egg white lysozyme

Abstract

White feces syndrome (WFS) is one of the major constrains for shrimp cultivation. Although the pathogen causing WFS remains largely unknown, WFS has been associated with an increase in vibrio abundances in shrimp haemolymph and intestine. We demonstrated that hen egg white lysozyme (HEWL) inhibited in vitro growth of Vibrio spp. including V. alginolyticus, V. harveyi, and V. parahaemolyticus. To alleviate shrimp losses from WFS, HEWL was supplemented into feed at 0.005, 0.025, 0.125, and 0.625 g/kg diet. Supplementation at 0.125 (HEWL0.125) and 0.625 (HEWL0.625) g/kg diet retained the antimicrobial activity under the cultivation water. Both of the supplemental levels also showed a significant antimicrobial activity and reduction in vibrio richness in shrimp gastrointestinal tract. We further analyzed the effect of HEWL supplementation on the expression of immune and antioxidant related genes in hepatopancreas. HEWL0.125 substantially upregulated the expression of prophenoloxidase, serine proteinase, superoxide dismutase, thioredoxin, and ferritin. Growth performance analysis of weight gain, average daily gain (ADG), feed conversion ratio, and survival rate was also determined, but there were no differences in those parameters. When shrimp were challenged with a pathogenic strain of V. harveyi, we observed the greater survival rate in HEWL0.125 than that of the control group (66.67% vs. 16.67%). Importantly, the effect of HEWL0.125 on WFS was evaluated in a shrimp farm. The incidence of WFS was disappeared without recurrence in shrimp fed HEWL0.125. As a result, the survival and ADG were improved significantly. In conclusion, dietary supplementation of HEWL0.125 could inhibit vibrio growth and stimulate immune- and antioxidant-related gene expression leading to resistance against WFS in shrimp.