Effects of dietary Scutellaria baicalensis extract on growth performance, immune-related genes expression, and resistance against Vibrio parahaemolyticus in white shrimp (Litopenaeus vannamei)

In this study dietary Scutellaria baicalensis extract (SBE) was used to improve the shrimps' immune response and its resistance to Vibrio parahaemolyticus. SBE obtained by solid-liquid extraction (SLE) has shown stronger antibacterial activity against V. parahaemolyticus compared to extracts obtained through the pressurized liquid extraction (PLE) method. A stronger immune response, such as the production of reactive oxygen species and the induction of expression of immune genes in hemocytes was seen in the SBE (SLE) treated group in vitro. SBE (SLE) had better immune stimulation effects and bactericidal activity than SBE (PLE) and therefore was chosen for in vivo feeding trial. The group fed with 1% SBE showed a better growth performance after 2 weeks of the feeding trial, but the growth-promoting effects did not last until the end of the trial at week four. Higher SBE intake reduced shrimp resistance to V. parahaemolyticus on week two but showed better resistance than the control group on the fourth week. Gene expression assays were used to investigate contradictory responses of the SBE-fed groups to V. parahaemolyticus at different times. Most of the genes examined in the selected tissues were not significantly changed, suggesting that the higher mortality of shrimp fed with high dose of SBE was not due to suppression of immune-related genes at earlier time point. Collectively, the bioactivity of SBE is influenced by the extraction conditions. Higher dietary doses of SBE (1% and 5%) improved the resistance of the white shrimp to V. parahaemolyticus after a longer feeding period (week four), but caution should be taken when applying SBE in the feed since a vulnerable status (week two) was seen during the feeding trial.