Abstract
Simple SummarySperm maturation (acquisition of the potential for motility and fertilization by morphologically developed spermatozoa) in sturgeons is atypical of ray-finned fishes: it occurs outside the testes during the transit of testicular spermatozoa through the kidneys into the Wolffian ducts. We recently developed a method in which testicular spermatozoa of sterlet Acipenser ruthenus are matured in vitro when incubated in seminal fluid derived from Wolffian duct sperm. In this study, we explored whether in vitro maturation of testicular spermatozoa depends on the environmental temperature and/or hormonal stimulation of spermiation. We studied spermatozoa motility parameters after in vitro maturation of testicular sperm, concentrations of sex steroid hormones and testis morphology in sterlet males at different stages of male preparation for spawning with and without hormonal induction of spermiation. The obtained data suggest that the ability of testicular spermatozoa to be matured was not related to the environmental temperature, while hormonal stimulation was an absolute requirement for optimal in vitro maturation. The use of in vitro matured testicular spermatozoa might have considerable potential in aquaculture or conservation programs, which can be realized in cases of accidental death of valuable broodstock or failure to obtain Wolffian duct sperm of high quality.Sturgeon sperm maturation occurs outside the testes during the transit of testicular spermatozoa (TS) through the kidneys and the Wolffian ducts. A method of in vitro TS maturation in sterlet Acipenser ruthenus was used to investigate the effects of temperature and hormonal stimulation of spermiation on the ability of TS to complete this process. Spermatozoa motility parameters after in vitro maturation of testicular sperm, concentrations of sex steroid hormones and testis morphology were studied in three groups of sterlet: (1) after overwintering in ponds (OW), (2) adapted to spawning temperature (ST), and (3) adapted to spawning temperature with hormonal induction of spermiation (ST-HI). Blood plasma concentrations of testosterone, 11-ketotestosterone and 17,20β-dihydroxy-pregnenolone increased significantly after hormonal induction of spermiation (group ST-HI). In all groups, TS were not motile. After in vitro sperm maturation, motility was up to 60% only in group ST-HI. The data suggest that the ability of TS to be matured in vitro was not related to the environmental temperature, while hormonal stimulation of spermiation during the spawning season was an absolute requirement for optimal in vitro maturation.
Highlights
Sturgeons (Acipenseridae) is an extant early diverged actinopterygian fish family [1]
Sperm consists of spermatozoa and seminal fluid, while testicular sperm of sturgeons passes through the kidneys and the Wolffian ducts, where it is mixed with urine
We have shown that final spermatozoan maturation in sturgeons can be achieved within in vitro conditions by pre-incubation of testicular sperm in urine or in the seminal fluid of sperm collected from Wolffian ducts which is the site where sperm and urine are mixed naturally [3]
Summary
Sturgeons (Acipenseridae) is an extant early diverged actinopterygian fish family [1]. The morphology of their reproductive system is quite different from that in teleostean species. Sperm consists of spermatozoa and seminal fluid, while testicular sperm of sturgeons passes through the kidneys and the Wolffian ducts, where it is mixed with urine. Sturgeon sperm contains spermatozoa, seminal fluid and urine (for details, see review [2]). This anatomical feature determines a unique sperm maturation process: testicular spermatozoa (TS) acquire the ability for motility activation and fertilization only after mixing with urine [3,4]. We have shown that final spermatozoan maturation in sturgeons can be achieved within in vitro conditions by pre-incubation of testicular sperm in urine or in the seminal fluid of sperm collected from Wolffian ducts which is the site where sperm and urine are mixed naturally [3]
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