Embryonic temperature influences transcriptomic and methylation profiles in the liver of juvenile largemouth bass

Understanding the impacts of environmental conditions at early life stages on phenotypes and physiological responses to thermal variability at later stages is crucial for elucidating adaptive strategies in fish species. This study investigated the lasting effects of embryonic temperature on the growth performance, transcriptomic profiles, and CpG methylation status of juvenile largemouth bass (Micropterus salmoides) under normal and heat stress (HS) conditions. Embryos were incubated at three temperatures (22 °C, 25 °C, and 28 °C), reared at a constant 25 °C for three months, and subjected to acute HS at 37 °C. Liver samples were collected before and after HS for mRNA sequencing and reduced representation bisulfite sequencing. Significant differences in body size, body weight, condition factor, and hepatosomatic index were observed among groups. Fish hatched at 28 °C displayed a significantly higher standard length and body weight and lower hepatosomatic index than those hatched at lower temperatures. PCA analysis and Venn diagrams based on transcriptomes revealed transcriptomic response to HS differed at 28 °C while 22 and 25 °C were similar. Heat shock protein genes followed a similar trend. Epigenetic analyses revealed distinct CpG methylation patterns across incubation groups, while DNA methylation barely contributes to transcriptional differences. Under HS, different incubation groups exhibit various DNA methylation alterations. The "Neuroactive ligand-receptor interaction" pathway appeared to play an important role in the response to HS, suggesting a potential involvement of epigenetic regulation. Additionally, the atrnl1 gene may be involved in a DNA methylation-mediated regulatory mechanism in response to HS.