Zebrafish Tumor Necrosis Factor Receptor Superfamily Member 13B (TNFRSF13B), also known as Transmembrane Activator and CAML Interactor (TACI), is an immune receptor that plays an important role in regulating B cell development, survival, and antibody responses in zebrafish (Danio rerio). TNFRSF13B is a member of the tumor necrosis factor receptor (TNFR) superfamily and is expressed primarily on B lymphocytes and other immune cells. Zebrafish TNFRSF13B binds the ligands BAFF (B cell activating factor) and APRIL (A Proliferation-Inducing Ligand), triggering intracellular signaling pathways such as NF-κB and MAPK that regulate B cell activation, proliferation, differentiation, and immunoglobulin production. Through these mechanisms, TNFRSF13B contributes to the maintenance of humoral immunity and immune homeostasis in zebrafish. In cell culture, recombinant zebrafish TNFRSF13B or ligand-binding assays are used to study receptor–ligand interactions and signaling pathways involved in B cell activation and immune regulation. Zebrafish TNFRSF13B is also studied in zebrafish immune models to better understand the evolution and function of adaptive immunity and B cell signaling pathways in vertebrates.