Effects of acute cold stress and rewarming on the metabolism of gill tissue of Qingtian paddy field carp（Cyprinus carpio var. qingtianensis）

【Objective】 Qingtian paddy field carp（Cyprinus carpio var. Qingtianensis，PF carp）was frequently exposed to the stress of acute cold stress in ambient temperatures in shallow water environments. The study aimed to investigate the physiological response mechanism of PF carp in acute cold stress and rewarming，which could provide basis for scientific overwintering of PF carp and breeding of low-temperature-tolerant varieties. 【Method】 The metabolic peaks in gill tissue of PF carp were extracted by liquid chromatography-mass spectrometry（LC-MS）non-targeted metabolomics in the 9.0 ℃ cold stress for 6 h（CO group）and subsequent rewarming recovery to 28.0 ℃ for 6 h（RE group）and the 28.0 ℃ control group（Con group）. The pre-processed metabolomics data were matched with the database to identify the metabolites. The reliability of metabolomics data was identified by principal component analysis（PCA）and orthogonal least-squares discriminant analysis（OPLS-DA）. The differential metabolites between groups were screened according to the P value of Student’s test（P<0.05）and the variable weight value of OPLS-DA model（VIP>1）. The KEGG signal pathway enrichment analysis of differential metabolites was performed. The metabolic pathways mostly associated with acute cold stress and rewarming were screened by Fisher test. Cluster heat maps were made for important metabolic pathways to show the differences between groups and the changing trend of metabolite content. 【Result】 The PCA and OPLS-DA analysis showed that samples were aggregated within group，and were separated between groups. There were significant differences in metabolite levels between groups. The OPLS-DA score chart showed that the cumulative Q² values of all groups were above 0.5，and the cumulative R²Y values were close to 1.0. The model had high interpretability and reliability. A total of 1222 metabolites were identified，among which 232，238，300 significantly different metabolites were screened and identified respectively in CO vs Con，RE vs CO and RE vs Con（P<0.05）. Differential metabolism between groups were mainly enriched in metabolic pathways such as arachidonic acid metabolism，glycerophospholipid metabolism，steroid hormone biosynthesis and purine metabolism. Specifically，under acute cold stress，cortisol levels was up-regulated，but arachidonic acid and its metabolites，glycerophospholipid metabolites were down-regulated. After rewarming，the metabolism of arachidonic acid and glycerophospholipid，purine metabolism were down-regulated compared with Con group，while the content of cortisol was down-regulated and the content of taurine was up-regulated. 【Conclusion】 Acute cold stress can lead to immunosuppression，abnormalities in substance transport and signal transmission in PF carp. Cortisol synthesis and metabolism are important mechanisms for resistance to acute cold stress. Gill tissue damage can not be fully recovered in the short term after rewarming. Taurine synthesis may be an important recovery mechanism of PF carp after rewarming.