Seasonality of reproduction in male spotted murrel Channa punctatus: correlation of environmental variables and plasma sex steroids with histological changes in testis.

The present study was undertaken to develop a comprehensive understanding of how environmental cues and sex steroids relate with cyclic changes in spermatogenesis in freshwater spotted snakehead Channa punctatus that is nutritious and economically important. The seasonal histological changes in testis and annual profile of gonadosomatic index (GSI) of C. punctatus delineated the testicular cycle into four phases: regressed (December-March), preparatory (April-June), spawning (July and August) and postspawning (September-November). Among environmental variables, correlation and regression analyses exhibited an important relationship between photoperiod and testicular weight while role of rainfall was seen confined to spawning. The seasonal profile of plasma sex steroids when correlated with cyclic changes in spermatogenesis in spotted snakehead, testosterone (T) seems to be involved in controlling the major events of spermatogenesis from renewal of stem cells to spawning of spermatozoa. Another important androgen prevalent in teleosts, 11-ketotestosterone (11-KT), was high during preparatory phase, suggesting that 11-KT in addition to T plays an important role in progression of spermatogenesis and spermiation in C. punctatus. However, 11-KT was not seen to be associated with milt production and release of spermatozoa during spawning. Plasma profile of estradiol-17β (E2) during different reproductive phases revealed the involvement of E2 in repopulation of stem cells during postspawning phase and in maintaining quiescence of testis during regressed phase.