Response of rice flower carp (Cyprinus carpio var.) to high-temperature stress: Mechanisms and limits of tolerance

Climate change presents a considerable challenge to the sustainable development of aquaculture. Research on the impact of high-temperature stress on rice flower carp (Cyprinus carpio var.) is still limited. In this study, rice flower carp (Cyprinus carpio var.) were exposed to four temperature treatments for 14 days: CK (control, 26 °C), TL (low temperature, 28 °C), TM (medium temperature, 30 °C), and TH (high temperature, 32 °C). The findings revealed that high temperatures significantly influenced the diversity of gut microbiota. Moreover, high-temperature stress disrupted the structural integrity of intestinal and liver tissues, causing notable damage. It also impaired the antioxidant system, leading to the accumulation of malondialdehyde (MDA) and inducing oxidative stress. At the transcriptional level, differentially expressed genes (DEGs) associated with the protein processing pathway (e.g., HSP40, HSP70, Bip) and the PPAR (peroxisome proliferator-activated receptor) signaling pathway (e.g., PPARδ, CPT1) were significantly upregulated during temperature acclimation. However, further temperature increases inhibited their expression, highlighting their crucial roles in the high-temperature acclimation of rice flower carp. In conclusion, rice flower carp displayed a degree of tolerance to temperatures up to 30 °C. Beyond this threshold, their health and physiological functions were adversely affected. Our study provides a valuable reference for understanding the impact of high-temperature stress on aquatic animals.