The present study demonstrates seasonal variation in the cellular expression of neuropeptide Y (NPY), a known orexigenic neuropeptide, in the testis of the catfish, Clarias batrachus and its relation with testicular steroids. In vitro effects of NPY on androgen production and activities of steroidogenic enzymes were also analyzed to reaffirm the relation between NPY and steroids. NPY-immunoprecipitation was observed in Sertoli cells, interstitial cells and germ cells in recrudescing testis. Intensity of NPY-immunoreaction in the interstitial cells increased steadily with initiation of spermatogenesis and reached maximal in fully grown testes, and then decreased suddenly in the spermiating/spent testis. NPY was also expressed considerably in Sertoli cells in recrudescing testis, but disappeared in the fully grown testis. A moderate NPY-immunoreactivity was also seen in spermatogonial cells in recrudescing testis, but intense NPY-immunoprecipitation was detected in advanced germ cells (spermatids/spermatozoa) in fully mature testis. NPY-immunoreation intensity in interstitial cells showed positive correlation with increasing levels of testicular testosterone and 11-ketotestosterone, and with activities of 3β-HSD & 17β-HSD coinciding with advancing testicular activities. NPY treatment of testicular fragments in vitro stimulated the activities of 3β-HSD & 17β-HSD and increased testosterone & 11-ketotestosterone levels. This study for the first time demonstrates the existence of NPY peptide at cellular levels in fish testis, which stimulates androgen production by acting directly at testicular level.