Study on the potential impact of sustained high temperatures during non-breeding season on largemouth bass
With the growing scale of largemouth bass breeding, the demand for seedlings is increasing. As global temperatures rise, it is crucial to study the effects of high temperature their regulatory mechanisms in largemouth bass. In this study, we simulated a high water temperature (28 ?) in the non-breeding season in aquaculture ponds for 28 days to examine the growth, reproduction, metabolism, apoptosis, and methylation markers in largemouth bass; transcriptome analysis was also performed. The results showed no significant difference in body weight between male and female largemouth bass. However, the high-temperature exposed females had reduced growth hormone (GH) and estradiol (E2) levels and elevated cortisol levels. They also showed upregulated expression of AR, cyp19a, igf, fshß, and lhß in ovarian tissue. Transcriptomic comparisons between temperature treatments revealed 963 differentially expressed genes in females and 700 in males. Both the ECM receptor interaction and PPAR signaling pathways were significantly enriched. High-temperature enhanced the lipid metabolism process through the PPAR signaling pathway. High temperatures increased oxidative stress in females, which corresponded with increases in SOD, CAT, and GSH-Px, likely to counteract the excess reactive oxygen species. Moreover, endoplasmic reticulum stress was activated, indicated by increases in IRE1 and ATF6, leading to the upregulation of apoptosis-related genes and ovarian cell apoptosis. At high temperature, 5-MC%, demethylase, and methyltransferase were not different in females, while 5-MC% and methyltransferase were higher and demethylase was lower in males. In summary, sustained high temperature affected ovarian development by altering the expression of hormone and gonad related genes and inducing endoplasmic reticulum stress leading to ovarian cell apoptosis. However, low demethylase activity and high genome-wide methylation in the testis suggested that high temperatures may affect testis development via methylation, potentially impacting offspring production. Overall design: A total of 216 fish were randomly divided into the 12 tanks, with 18 fish per tank, separate males and females. This experiment sets up 2 groups (three tanks/group), the temperature in the control group is maintained at 20°C, while in the high-temperature group, the temperature is increased to 28°C within 2 hours. Samples are taken at the beginning of the experiment as the IC group. After 28 days, the control group sample is taken as NC group, and the high-temperature group sample is taken as HT group