Transcriptome analyses reveal differences in the response to temperature in Florida and Northern largemouth bass (Micropterus spp.) during early life stages.

Temperature is one of the most relevant factors influencing the development of aquatic species, making it a key parameter to consider for aquaculture. Largemouth bass (LMB; Micropterus spp.) are highly relevant for human consumption and sport fishing, representing one of North America's most important freshwater fisheries. Yet, questions remain on how LMB raised in recirculating aquaculture systems (RAS) respond to different temperatures. The main objective of this study was to determine the impact of thermal rearing conditions (21°C, 24°C, and 27°C) on gene expression of Florida and Northern LMB larvae at 8- and 28-days post hatch (DPH). Using de novo transcriptomes as a reference, our results suggest that gene expression differences for Florida LMB were mostly associated with temperature, while differences for Northern LMB were controlled by temperature and developmental stage. In general, both lineages showed activation of molecular pathways associated growth, such as development of muscle, nervous system, and vascular system. There were molecular signatures of stress with warming as well, including immune function, apoptosis, regulation of inflammation, and heat shock proteins. Florida LMB showed large differences between temperatures at both stages, while differences were much larger for Northern LMB at 28 DPH, specifically for individuals reared at 27°C. The results from this study are in line with previous phenotypic studies that indicated faster growth at warmer temperatures and better performance of Northern LMB raised in RAS. Overall, this study exemplifies how controlling developmental temperatures during the critical early life stages can be essential to guarantee the success of commercial hatchery production techniques.