Effect Of Poly-Beta-Hydroxybutyrate On Growth, Enzyme Activity And Intestinal Microbial Community Of Chinese Mitten Crab, Eriocheir Sinensis (Milne-Edwards) Juveniles

Poly-beta-hydroxybutyrate (PHB) is microbial carbon and energy storage polymer, which can be degraded into water-soluble beta-hydroxybutyric acid in the gastrointestinal tract of aquatic animals. A 60-day culture experiment was performed using Chinese mitten crab, Eriocheir sinensis (Milne-Edwards) juveniles with an average initial body weight of 0.74 +/- 0.06 g which were fed a diet supplemented with 0%, 0.5%, 1%, 3% or 5% PHB. A PHB dietary supplementation of 1% and 3% significantly improved the body weight gain, moulting frequency and concomitantly reduced 2nd-3rd moulting intervals of the crabs (P < 0.05). The dietary PHB level positively related to hepatopan-creatic pepsin, trypsin and lipase activity (P < 0.05). Increasing the dietary PHB also improved total superoxide dismutase activity, but reduced alkaline phosphatase and acid phosphatase activity in the serum of hemolymph (P < 0.05). A 16S rRNA gene analysis by denaturing gradient gel electrophoresis indicated that PHB supplementation led to a significantly higher range-weighted richness, diversity and evenness of the gut bacterial community when dosed at 3% in the feed. The beneficial effects of PHB are discussed in terms of immune defense, metabolism and gut microbiota of the crabs.