Ontogeny and tissue-specific expression of immune-relevant genes in Catla catla (Hamilton)

India is the second largest fish producing country in the world with production of 12.6 million tonnes (mt) in 2017-18, and Indian major carps (IMCs) contribute bulk of this fish production. Catla, Catla catla is the fastest growing species among IMCs. However, the survival rate of catla during larval rearing is normally lower than the other IMCs i.e rohu Labeo rohita, and mrigal Cirrhinus mrigala. Continuous efforts are devoted for the identification of nutritional and environmental requirements of fish larvae in order to reduce hatchery mortalities. However, very little information is available regarding physiology of the immune system, especially during the late larval and juvenile stages. Hence, understanding the ontogenetic development of immune-relevant genes in the larval stages of catla will serve as the markers for the development of immune competence and thereby, will be beneficial in developing effective immune intervention strategies. In the present study, expression profiles of some of the important innate (IL-1β, IL-10, iNOS and C3) and adaptive immune (RAG-1, Ikaros, IgM and IgZ) genes during ontogenetic developmental stages and in different tissues of catla were investigated using quantitative real-time PCR. The results revealed that immune genes IL-1β, C3, IgM and IgZ were detected in the unfertilized eggs indicating their maternal inheritance. Immune genes, IL-1β, IL-10 and iNOS were expressed significantly during initial larval developmental stages whereas C3, RAG-1, Ikaros, IgM and IgZ showed significant expression during advanced stages of larval development in catla i.e. from 23 days post hatch (dph). Study of tissue distribution pattern of the genes indicated that innate immune genes were ubiquitously expressed in different tissues with varying degree of expression, whereas adaptive immune genes were predominantly expressed in lymphoid organs of catla. The information thus generated will improve knowledge on the maturation of the immune system in catla and will aid in deciding the appropriate age for vaccination in this teleost species.