Immunomodulatory effects of seagrass Halophila ovalis polysaccharide mixed feed in adult black tiger shrimp Penaeus monodon and its protective efficacy against white spot syndrome virus infection

As white spot syndrome virus (WSSV) can be highly pathogenic in penaeid shrimp, various feed supplements have been tested to help to protect farmed shrimp against WSSV disease. Here a polysaccharide extract from Halophila ovalis (HO) seagrass was added to feeds at concentrations of 0.25, 0.5, and 1.0 g[a1] /kg to assess its ability to protect Black Tiger shrimp (Penaeus monodon) against WSSV challenge. Following feeding on these diets for 25 days, P. monodon were challenged by muscle injection and monitored for 21 days. On Day 0 and on Days 7 and 21 post-injection (pi), total haemocyte counts (THC), total protein concentrations, prophenoloxidase activity and respiratory burst activity were compared using haemolymph collected from 10 shrimp. All shrimp fed the basal diet died by Day 7 pi but survival times were extended among shrimp fed diets containing HO polysaccharide (HOP), and significantly at concentrations of 0.5 or 1 gkg-1. Concomitantly with improved survival, all haemolymph immune parameters examined were enhanced significantly (p<0.05) among shrimp fed diets containing higher amounts of HOP. WSSV infection loads determined by real-time PCR were also lowered. The data suggest that if shrimp growth performance is not affected, inclusion of 0.5-1 gkg-1 HOP in commercial feeds might increase resilience of pond stocks of P. monodon against WSSV disease and when disease occurs, provide farmers with a longer management window to minimize economic losses.  [a1]Change to gkg-1