Gouania willdenowi is a teleost fish without immunoglobulin genes.

Immunoglobulin (Ig) genes encode antibodies in jawed vertebrates. They are essential elements of the adaptive immune response. Ig exists in soluble form or as part of the B cell membrane antigen receptor (BCR). Studies of Ig genes in fish genomes reveal the absence of Ig genes in Gouania willdenowi by deletion of the entire Ig locus from the canonical chromosomal region. The genes coding for integral BCR proteins, CD79a and CD79b, are also absent. Genes exist for T α/β lymphocyte receptors but not for the T γ/δ receptors. The results of the genomic analysis are independently corroborated with RNA-Seq transcriptomes from other Gobiesocidae species. From the transcriptome studies, Ig is also absent from these other Gobiesocidae species, Acyrtus sp. and Tomicodon sp. Present evidence suggests that Ig is missing from all species of the Gobiesocidae family.