Investigating the Impact of Varied Dietary Protein Levels on ILitopenaeus vannamei/I: An Exploration of the Intestinal Microbiota and Transcriptome Responses

Five feed protein levels (32%, 36%, 40%, 44%, and 48%) were set up using fishmeal as the sole protein source to study the effects of different feed protein levels on the intestinal microbiota and transcriptome responses of L. vannamei. It was found that the optimal feed protein level for shrimp L. vannamei is between 40% and 44%. Excessively high or low feed protein levels reduce antioxidant levels and digestive enzyme activity and promote pathogen colonization. The transcriptional regulation of inappropriate protein levels responds to the body by reducing factors in various metabolic pathways. The weakened genes impede metabolic processes and compromise immunological function, increasing the organism’s vulnerability to diseases. This can impair the immune systems of shrimp and cause stunted growth. This study explored the effects of dietary protein levels on Litopenaeus vannamei with its intestinal microbiota and transcriptome responses. Previous studies on the effects of dietary protein levels on L. vannamei have focused on growth performance, antioxidant indices, and digestive enzyme activity, but few studies have been conducted at the microbiological and molecular levels. In this study, five isolipid experimental diets with protein levels of 32% (P32), 36% (P36), 40% (P40), 44% (P44), and 48% (P48) were used in an L. vannamei (0.63 ± 0.02 g) feeding trial for 56 days. At the end of the feeding trial, the growth performance, immunity, intestinal health, and transcriptional responses of L. vannamei were determined. This study demonstrated that higher protein levels (P44) led to superior weight gain and growth rates for L. vannamei, with lower feed conversion ratios (FCR) observed in the P48 and P44 groups compared to the P32 and P36 groups (p ≤ 0.05). The P44 and P48 groups also showed a notably higher protein efficiency ratio (PER) compared to others (p ≤ 0.05), and there was no significant difference between them. Upon Vibrio parahaemolyticus infection, the P48 group exhibited a significantly lower survival rate (SR) within 48 h, while during 72 h of white spot syndrome virus (WSSV) infection, the P44 group had a notably higher survival rate than the P32 group (p ≤ 0.05). Digestive enzyme activity and antioxidant levels in L. vannamei initially increased and then decreased as protein levels increased, usually peaking in the P40 or P44 groups. Lower dietary protein levels significantly reduced the relative abundance of beneficial bacteria and increased