Gambon Deza, F.

Immunoglobulin genes are a central component of jawed-vertebrate adaptive immunity. A previous study showed that the blunt-snouted clingfish Gouania willdenowi lacks immunoglobulin genes and T-cell receptor gamma/delta loci while retaining T-cell receptor alpha/beta genes, MHC genes, and RAG1/RAG2. Here, I extend this observation to Gobiesocidae using seven chromosome-level genome assemblies. Manual tblastn and synteny-guided searches found no convincing immunoglobulin heavy- or light-chain loci in G. willdenowi, Gouania pigra, Gobiesox punctulatus, Apletodon dentatus, Lepadogaster candolii, Lepadogaster purpurea, or Diplecogaster bimaculata. These results support root-level loss of canonical immunoglobulin genes in clingfishes. A targeted immune-gene screen further indicates family-wide erosion of B-cell/adaptive core genes, including CD79A, CD79B, CIITA, TNFRSF13B, and TNFSF13B. In contrast, TCR alpha/beta, MHC genes, and RAG1/RAG2 are retained, indicating that Gobiesocidae should not be described as lacking adaptive immunity altogether. A shared Gobiesocidae RAG2 PHD-domain C-to-S replacement provides a possible molecular context for antigen-receptor remodeling. These findings identify Gobiesocidae as a vertebrate family with ancestral loss of canonical antibody genes and associated erosion of the B-cell/humoral immune axis.