Beneficial effects of Haematococcus pluvialis on growth and hepatopancreas health status in crayfish (Procambarus clarkii) via remodeling the gut microbial metabolic functions

Abstract

Plant proteins fulfill roles in low-fishmeal diets for crustaceans, but their overuse could have negative effects. Haematococcus pluvialis has the potential to be used as a functional additive due to its high astaxanthin. As such, this study aimed to investigate the effects of dietary H. pluvialis supplementation on growth, hepatopancreas health, and gut metabolic functions in crayfish. 720 crayfish with average weight around 9.20 g were randomized into six treatments (HP0, HP0.3, HP0.6, HP0.9, HP1.2, and HP1.5) in three replications each, and fed six different dosages of H. pluvialis over sixty days. Crayfish exposed to H. pluvialis at concentrations of 0.3, 0.6, and 0.9 % showed significant increases in final average weight, weight gain rate, and specific growth rate (P < 0.05) compared to the HP0 group, together with the highest contents of muscle and shell astaxanthin in the HP0.9 group. Furthermore, increasing H. pluvialis supplementation exhibited the potential to repair hepatopancreas, as demonstrated by the decrease in hemolymph malondialdehyde (MDA) content and activities of alanine aminotransferase and aspartate aminotransferase, as well as the increase in the total protein content, superoxide dismutase, and glutathione peroxidase (GSH-Px) activities. Moreover, high H. pluvialis diets improved microbial dysbiosis by increasing specific microbes, the alpha diversity index, and shifting prominent phyla such as Proteobacteria and Firmicutes. Specifically, dietary H. pluvialis inclusion significantly decreased Vibrio (Proteobacteria) compared to the HP0 group (P < 0.05), but Tyzzerella (Firmicutes) showed the opposite regulatory pattern. A further statistical check revealed that 20 differential OTUs were shared by all H. pluvialis groups compared to the HP0 group, with OTU1439 and OTU2941 identified as the main growth-liver health contributors. Accordingly, high H. pluvialis diets contributed to more complex and stable microbial networks, and down-regulated alanine, aspartate, and glutamate metabolism, as well as lipopolysaccharide biosynthesis. Taken above, the optimal dietary H. pluvialis inclusion level was recommended to be 0.78–0.86 % according to the growth and astaxanthin contents. High H. pluvialis feeding reversed gut microbial dysfunction and improved hepatopancreas antioxidant capacity.