Effects of Astaxanthin on Growth Performance, Gut Structure, and Intestinal Microorganisms of Penaeus vannamei under Microcystin-LR Stress

Microcystin-LR (MC-LR) are biologically active cycloheptapeptide compounds that are released by cyanobacteria during water blooms and are extensively found in aquatic ecosystems. The Penaeus vannamei is a significant species in global aquaculture. However, the high level of eutrophication in aquaculture water frequently leads to outbreaks of cyanobacterial blooms, posing a significant threat to its sustainable cultivation. Astaxanthin (AX) is commonly utilized in aquaculture for its physiological benefits, including promoting growth and enhancing immune function in cultured organisms. This study aimed to examine the protective effect of astaxanthin on P. vannamei exposed to microcystin-induced stress. The experiment consisted of three groups: one group was fed formulated feed containing MC (100 μg/kg), another group was fed formulated feed containing MC (100 μg/kg) + AX (100 mg/kg), and the third group was fed basic feed (control group). After 15 days of feeding, the specific growth rate (SGR) was significantly higher in the MCAX group (2.21% day^-1) compared to the MC group (0.77% day^-1), and there was no significant difference between the MCAX group (2.21% day^-1) and the control group (2.24% day^-1). Similarly, the percent of weight gain (PWG) was also significantly higher in the MCAX group (14.61%) compared to the MC group (13.44%) and the control group (16.64%). Compared to the control group, the epithelial cells in the MC group suffered severe damage and detachment from the basement membrane. However, in the MCAX group, although there was still a gap between the intestinal epithelial cells and the basement membrane, the overall intestinal morphology was slightly less impaired than it was in the MC group. The analysis of the intestinal microbiota revealed a significant disparity in the community composition (chao 1 and ACE) between the MC and MCAX groups. When comparing the various bacterial genera, the MC group exhibited an increase in Vibrio abundance, whereas the MCAX group showed a decrease in both Shewanella and Vibrio abundance. The results indicate that AX has a positive impact on the growth performance and resistance of P. vannamei against MC by regulating the composition of the intestinal microbiota. AX can be utilized to mitigate the detrimental effects of MC in aquaculture practices. This function could be attributed to the role of AX in preserving the structural integrity of the intestinal mucosa and regulating the composition of the intestinal microbiota.