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 °C) 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, fshβ, and lhβ 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 test is suggested that high temperatures may affect testis development via methylation, potentially impacting offspring production.