author(s)
Ngairangbam Sushila, Basant Kumar Das, K Pani Prasad, Gireesh-Babu P, Paramita B Sawant and Gayatri Tripathi

abstract
The early larval stages of fish are susceptible to microbial infections until the maturation of lymphoid organs. Fishes are capable of responding the pathogens specifically by activating the adaptive immune system. During the maturation of lymphoid organs, phenomenon of V(D)J recombination is mediated by recombination activating genes (RAGs), which act as the marker of physiological maturity of the adaptive immune system. In the present study, the RAG-1 nucleotide sequence was partially cloned (272bp) in order to assess its pattern of mRNA expression in different tissues and during the larval developmental stages of Pterophyllum scalare. The RAG-1 mRNA expression was detected in early larvae right from the first day after hatching. Later, an up-regulation in the expression was observed upto 30 dph followed by a declined trend till the end of experiment. Moreover, the tissue distribution of RAG-1 revealed a significantly high expression level in kidney than other tissues which demonstrate it to be a major lymphoid organ. Hence, the current study concludes that the complete maturation and development of lymphoid organs based on the mRNA expression of RAG-1 occurs at 27 to 30 DPH in P. scalare.