Innate lymphoid cells (ILCs) have been extensively characterized in mammals such as mice and humans, however, the existence and function of ILCs in other vertebrates is poorly understood. We have characterized zebrafish ILC subsets and the conservation of the function of IL-22, an ILC-produced cytokine safeguarding epithelial integrity. We have used single-cell RNA sequencing to generate a comprehensive atlas of zebrafish lymphocytes during tissue homeostasis and following immune challenge. To study the sources and function of zebrafish IL-22, we generated an IL-22 reporter line as well as mutants for IL-22 and its receptor. We have found that this and other cytokines are already highly inducible in intestines even prior to the establishment of immune cells in this organ. We are currently investigating the function and cell sources of this developmentally early intestinal immune responses.