Effect of Temperature on Microbial Diversity and Predictive Function in the Intestine of Olive Flounder (Paralichthys olivaceus)

While the impact of the environment on the fish microbiome remains under discussion, studies on the intestinal bacterial diversity of olive flounder are still limited. This study investigated the effects of three temperature conditions, 15 °C (Group L), 20 °C (Group M), and 25 °C (Group H), on the structure and diversity of the bacterial community in the gut of olive flounder. During the 35-day experiment, changes were observed in the composition and diversity of the gut microbiota, with alpha diversity estimates gradually decreasing as the temperature increased. At the species level, there were significant differences in the relative abundance of Sphingomonas echinoides and Photobacterium damselae between Groups L and H. According to LEfSe and correlation analyses, the relative abundances of Gammaproteobacteria, Alphaproteobacteria, Sphingomonas, and Photobacterium varied significantly depending on temperature levels. Through functional prediction, the predicted functional pathways based on bacterial abundances showed that those involved in aromatic compound degradation and amino acid metabolism were abundant in Group L, whereas pathogenic factors were abundant in Group H, suggesting a potential impact on host digestive and immune functions. These results suggest that temperature can significantly affect both the diversity and potential functional profiles of the intestinal microbiota in olive flounder.