Interferons (IFNs) represent a pivotal family of cytokines that were first identified decades ago, serving as key mediators of the immune response in eukaryotic organisms. Synthesized and secreted by both immune cells (such as macrophages, lymphocytes) and non-immune cells (including fibroblasts and epithelial cells) upon stimulation by pathogens, environmental stressors, or cellular abnormalities, IFNs are naturally occurring glycoproteins characterized by diverse biological activities. Beyond their well-documented broad-spectrum antiviral and antiproliferative properties, IFNs exert profound immunomodulatory effects, orchestrating cellular differentiation, growth, and metabolism through intricate signaling cascades. These pathways are tightly regulated to mount effective responses against tumorigenesis, viral infections, bacterial invasions, and other inductive factors, making IFNs central to the crosstalk between innate and adaptive immunity in vertebrates. As core components of humoral immunity, B cells play an irreplaceable role in the immune system by initiating and regulating humoral immune responses. In mammals, B cells primarily function in antibody production, antigen presentation, and the formation of immune memory. However, bony fish B cells exhibit unique functional plasticity that distinguishes them from their mammalian counterparts-they possess potent phagocytic capabilities comparable to macrophages, enabling them to directly participate in pathogen clearance and immune regulation through multiple mechanisms. Recent advances in fish immunology have demonstrated that type I IFNs in teleosts can modulate the activation and differentiation of B lymphocytes, thereby enhance systemic antibody levels and strengthen adaptive immune defenses. In contrast, research on type II IFN (IFNγ) in bony fish has been predominantly focused on its role in regulating macrophage antigen presentation and pro-inflammatory responses, while its functional interactions with B cells remain poorly understood. This critical research gap hinders a comprehensive understanding of the IFN-mediated immune network in bony fish and necessitates further in-depth investigation. Nile tilapia (Oreochromis niloticus) belongs to the genus Oreochromis, family Cichlidae, within the order Percomorpha. It is one of the key aquaculture species recommended by the Food and Agriculture Organization of the United Nations (FAO) and ranks as the world's second most commercially farmed fish species. China leads the world in Nile tilapia production. Affected by factors such as rearing environments and farming practices, tilapia frequently suffer from diseases, a problem that is becoming increasingly severe. Edwardsiella piscicida (E. piscicida) is one of the primary pathogens causing these diseases, resulting in significant annual economic losses for the aquaculture industry. Despite extensive research on IFNs in mammals, the regulatory mechanisms of IFNs-particularly their interactions with B cell function-remain incompletely elucidated in bony fish. As the key taxon in vertebrate immune evolution, bony fish bridge the evolutionary gap between invertebrates and higher vertebrates, possessing an immune system that combines primitive innate immune traits with early adaptive immune characteristics. Thus, deciphering the regulatory networks between the IFN system and B cells in bony fish is crucial for advancing our understanding of vertebrate immune evolution. Furthermore, existing studies on fish IFNs have been disproportionately focused on cold-water species such as rainbow trout (Oncorhynchus mykiss) and flounder (Paralichthys olivaceus), while research on tropical aquaculture species like Nile tilapia remains largely unexplored. Given the unique ecological and physiological traits of tropical fish, findings from cold-water species cannot be directly extrapolated, highlighting the necessity of targeted research on Nile tilapia. The present study aimed to investigate the immunoregulatory effects of type I interferon IFNc and type II interferon IFNγ on IgM+ B cells in Nile tilapia (Oreochromis niloticus). Recombinant IFNc (rOnIFNc) and IFNγ (rOnIFNγ) proteins were successfully expressed and purified using an Escherichia coli prokaryotic expression system. The optimal working concentrations of these proteins were determined via gradient concentration screening. Flow cytometry and quantitative real-time PCR (qRT-PCR) were employed to assess the effects of both proteins on the survival, phagocytic activity, antigen-presenting capacity, and transcription levels of immune-related factors in IgM+ B cells from peripheral blood and spleen. The results showed that the optimal concentrations for regulating Nile tilapia IgM+ B cells were 100 ng/mL for both rOnIFNc and rOnIFNγ. Neither rOnIFNc nor rOnIFNγ significantly affected the survival or antigen presentation capacity of IgM+ B cell. Notably, rOnIFNc specifically enhanced the phagocytic activity of IgM? B cells against Edwardsiella piscicida, the causative agent of tilapia edwardsiellosis, while showing no significant effect on their phagocytosis of fluorescent microspheres. This discovery not only expands our understanding of the multifunctional role of interferon in Nile tilapia but also offers new insights into the cross-regulation between humoral immunity and innate immunity in bony fish. Existing research lacks sufficient understanding of the interaction mechanisms between the Nile tilapia interferon system and pathogenic bacteria, hindering the development of highly effective immune control technologies. This study confirms that Nile tilapia type I interferon-IFNc enhances immune responses by regulating the phagocytic function of IgM+ B cells against pathogenic bacteria. This suggests interferon may enhance B cells recognition and clearance of specific pathogens by modulating specific receptors or signaling pathways, providing direct theoretical support and potential targets for developing targeted immune enhancers or adjuvants. Furthermore, this study reveals the potential role of IFNc in enhancing B-cells antibacterial immunity, providing theoretical support for developing interferon-based immune control strategies. It holds practical significance for advancing the healthy aquaculture of Nile tilapia. In summary, this study not only deepens our understanding of the immunological mechanisms by which teleost interferons regulate B cells, but also lays a solid foundation for innovative fish disease prevention and control technologies.