Abstract

Background: Flavobacterium oreochromis has been associated with elevated mortality rates during the early stages of tambaqui (Colossoma macropomum) aquaculture. This study investigated genetic responses to bacterial infection in juvenile fish by comparing gene expression profiles between symptomatic (IS) and asymptomatic (IA) individuals. Methods and results: Skin samples from both IA and IS individuals were collected for transcriptome sequencing. Approximately 21 million reads per library were aligned to the tambaqui genome. Differential expression analysis revealed 2,176 upregulated and 1,219 downregulated genes in IS individuals, whereas 1,358 genes were upregulated and 488 downregulated in IA individuals. Notably, genes upregulated in both groups were associated with autophagy (e.g., atg4b and ulk2) and oxidative stress responses (e.g., klf9 and txnip). In contrast, genes related to tissue integrity, such as unc45b and akap6, were consistently downregulated during infection. These results suggest a dual host response to F. oreochromis infection, characterized by activation of cellular stress pathways and the suppression of genes involved in maintaining structural integrity. The upregulation of autophagy-related (atg4b, ulk2) and oxidative stress-regulating (klf9 and txnip) genes likely reflects an attempt by the host to counteract bacterial invasion through enhanced intracellular degradation and redox homeostasis. Conversely, the downregulation of unc45b and akap6 may indicate a compromise in structural defense mechanisms. Conclusion: These findings offer valuable insights into the immunogenetics of tambaqui and have direct implications for enhancing disease resistance in aquaculture. Moreover, they contribute to a better understanding of the complex interplay between molecular pathways involved in F. oreochromis infection. © The Author(s), under exclusive licence to Springer Nature B.V. 2025.