Short-term adaptability to non-hyperthermal stress: Antioxidant, immune and gut microbial responses in the red swamp crayfish, Procambarus clarkii

Abstract

Thermal stress is a common experience suffered in rice-crayfish integrated systems (RCIS) by the red swamp crayfish, Procambarus clarkii. Based on our previous studies, the adaptability of this crayfish to non-hyperthermal stress over a specified period was explored within a short term by investigating the antioxidant capacity, immune function, HSP70 expression and intestinal microbial changes. Under the non-hyperthermal stress temperature (30 °C) determined by cumulative survivals, the malondialdehyde (MDA) content, total antioxidant capacity (T-AOC), total super oxide dismutase (T-SOD) and catalase (CAT) activities in hepatopancreas significantly increased to the peak values during at 12 h or 24 h (P < 0.05), respectively, and then gradually recovered to the levels of the controls (24 °C) (P > 0.05); the immune-related enzymatic activities (alkaline phosphatase, AKP; acid phosphatase, ACP; lysozyme, LZM) and gene expressions (TNFAIP, TNF and Toll) rapidly increased and reach the peaks at 12 h and 48 h, respectively, and maintained subsequently the higher levels compared with the controls (P < 0.05) except for TNFAIP. The relative expressions of HSP70 in the hepatopancreas, intestine and gill all increased sharply and reached the peak at 6 h (P < 0.05), then decreased fast and roughly returned to the levels of the controls at 96 h (P > 0.05), while, there was still a relatively high expression during the later stages in the gill. High-throughput sequencing of 16S ribosomal DNA revealed the thermal stress altered the diversity and composition of intestinal microbiota. The increased abundance of Proteobacteria and decreased abundance of Bacteroidetes (mainly Bacteroides) and Firmicutes might be indicative of the elevated microbial instability and the unnecessity for high level of nutrient metabolism in the host. The abundance increase of relevant metabolic pathways (e.g., the biosynthesis and degradation of amino acids and lipids) predicted by MetaCyc might be caused by the abundance increase of Proteobacteria. The decreased abundance of two phyla (Actinobacteria and Fusobacteria) and genus Anaerorhabdus could adversely affect the crayfish's intestinal health status. While, the obvious abundance decrease of putatively opportunistic genera (Shewanella and Acinetobacter), combined with the abundance increase of beneficial phylum Tenericutes and genus Rhodobacter, suggested that there concurrently existed some adaptability to the non-thermal stress, which did not resulted in apparent risks of intestinal disorder. This study provides insights into the underling adaptive mechanisms associated with the anti-oxidation, immunity, intestinal microflora and nutrient metabolism of P. clarkii in response to the short-term non-hyperthermal stress.