β-Hydroxy-β-methylbutyrate supplementation in a low protein diet: Implications on hemolymph parameters, immunity, endoplasmic reticulum stress and hepatopancreas histology of kuruma shrimp (Penaeus japonicus)

Our previous study revealed that inclusion of β-hydroxy-β-methylbutyrate (HMB) in a low protein diet ameliorated the growth and muscle quality of kuruma shrimp ( Penaeus japonicus ) with a high dietary protein requirement. The impact of low protein diet supplemented with HMB on health status of P. japonicus was then investigated in this study. The diets with 49 % and 44 % crude protein were used as the control diet (HP) and low protein diet (LP) respectively. The 0.025 %, 0.05 %, 0.10 %, 0.20 % and 0.40 % of β-hydroxy-β-methylbutyrate calcium were added to the LP diet to formulate the other five diets respectively. Shrimp (initial body weight: 2.00 ± 0.01 g) were fed with these seven diets for 56 days. Results indicated that compared with the HP group, shrimp fed LP exhibited significantly lower contents of total protein and albumin in hemolymph, and activities of catalase, glutathione peroxidase, acid phosphatase, alkaline phosphatase and lysozyme (LZM) in hepatopancreas, while significantly higher activities of alanine transaminase (ALT) and aspartate transaminase in hemolymph, and malondialdehyde (MDA) content in hepatopancreas. However, proper inclusion of HMB in the LP diet restored the aforesaid parameters except ALT. Dietary HMB supplementation mitigated the declines in transcriptions of genes related to prophenoloxidase system ( propo , ppaf and lgbp ), toll-like receptor pathway ( tlr1 , tlr3 and traf6 ) and antimicrobial peptides ( alf , crustin and pen ) in hepatopancreas of shrimp fed LP. Meanwhile, supplementing 0.20 % HMB alleviated the increment of endoplasmic reticulum stress-related genes ( grp78 and xbp1 ) expression and histopathological damage of hepatopancreas induced by the LP diet. In conclusion, dietary HMB could improve anti-oxidative capacity and immunity of P. japonicus fed a low protein diet. The optimal inclusion level of HMB in the LP diet for P. japonicus was estimated to be 0.24 % and 0.35 % by the quadratic regression analysis with MDA content and LZM activity of hepatopancreas, respectively. • Effects of dietary HMB on health status of kuruma shrimp fed a low protein diet (LP). • The LP group had poorer anti-oxidative capacity and immunity. • The LP group exhibited histopathological damages in hepatopancreas. • Inclusion of HMB in LP diet improved anti-oxidative capacity and immunity of shrimp. • Dietary HMB alleviated the histopathological damages in hepatopancreas.