Effects of photoperiod on spermatogenesis inGambusia affinis holbrooki(Teleostei: Poecilidae) during the period of testicular quiescence

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.

Seasonal reproduction of male Gambusia holbrooki (eastern mosquitofish) from two Florida lakes

Sixteen monthly collections of adult male Gambusia holbrooki (eastern mosquitofish) were obtained from two lakes in central Florida, USA. Lake Woodruff and Lake Apopka are 36 miles apart, but differ in several environmental parameters. Compared with Lake Woodruff, Lake Apopka is warmer, more shallow in sampling areas (particularly during drought conditions; approximately 15-90 cm in Lake Apopka versus 60-120 cm in Lake Woodruff), more turbid, and more heavily contaminated with nutrients and industrial and agricultural chemicals. Here, we present detailed information on seasonal reproduction patterns in mosquitofish in their native range and compare patterns between fish from the two lakes. Male mosquitofish were reproductively active from spring through fall. Spermatogenesis, which is regulated in part by 11-ketotestosterone, ceased in October, and fish stored spermatozoa through the winter for immediate fertilization of offspring in the spring. Compared with Lake Woodruff, fish from Lake Apopka tended to be larger and have longer gonopodia and greater gonado- and hepato-somatic indices (GSI and HSI). High GSI in Apopka fish correlated with greater spermatid production, but fewer mature spermatozoa and either the same or lower sperm counts and sperm viability. Taken together, these observations suggest that differentiation of spermatids to spermatozoa is disrupted in Apopka fish, leading to reductions in fertility in some months. Delivery of sperm to females could also be affected in Apopka fish, which exhibit lower prevalence of efferent duct tissue in the testes during the summer.