Pikeperch (Sander lucioperca) spermatozoa motility and volume regulation under different osmotic and ionic conditions.

Pikeperch (Sander lucioperca) is a highly profitable commercial species whose economic value has greatly increased in the last decade. As in other species, the quality of spermatozoa in this species is a principal feature inherent in fertilization success and efficient natural and artificial reproduction. The capacity of fish spermatozoa to be activated and tolerate environmental changes (in osmolality, ion composition, external pH, temperature, etc.) during the motility period contributes to fertilization success. In this study, we investigated the effects of environmental osmolality and ion composition on spermatozoa motility. To determine if the activation mechanism is affected by sperm quality parameters, we measured semen characteristics such as semen volume, spermatozoa concentration, seminal fluid osmolality and ion composition, and spermatozoa lipid composition. An additional parameter of sperm quality reflecting spermatozoa osmoresistance, the swelling rate, was measured by the nephelometry method. We detected that sperm samples with the highest content of palmitic (C16:0) and palmitoleic (C16:1) acids showed the lowest motility activation under the studied conditions, suggesting that these fatty acids are possible markers for the determination of spermatozoa quality in fish. Our results show that pikeperch spermatozoa can be activated under different osmotic conditions and that cell swelling always accompanies motility. However, spermatozoa sustain their volume under hypotonic conditions when motility is not initiated, suggesting that pikeperch spermatozoa activation is mainly controlled by ion composition rather than the osmolarity of the surrounding medium.

Spawning Performance and Sex Steroid Levels in Female Pikeperch Sander lucioperca Treated with Poly(lactic-co-glycolic acid) Microparticles.

Pikeperch Sander lucioperca is a piscivorous species considered a promising candidate for the diversification of intensive aquaculture. This study aimed to determine the effect of a sustained-release delivery system incorporating mammalian gonadotropin-releasing hormone agonist (mGnRHa) into poly(lactic-co-glycolic acid) (PLGA) microparticles on the sex steroid levels and aspects of artificial reproduction of pikeperch. Fish were divided into four groups and injected with 20 µg mGnRHa/kg, 5-day release microparticles encapsulated with 5 µg GnRHa/kg BW (PLGA 5), 20 µg GnRHa/kg (PLGA 20), or 1 mL/kg 0.9% NaCl (control). Cumulative percentage ovulation was 100% in the PLGA 5 group, significantly higher than in other tested groups. No differences among groups were observed in latency or fecundity. The level of 11-ketotestosterone (11-KT) peaked at 40 h post-injection, and was sustained during ovulation, in all treated groups. The 17ß-estradiol (E2) concentration increased in the mGnRHa-only group immediately after hormone injection, while both PLGA groups showed a reduction in E2 after injection, continuing to decrease until ovulation. A low dose of mGnRHa in PLGA microparticles significantly improves induction of ovulation and results in acceptable reproductive performance, which may positively affect pikeperch production under controlled conditions.

Induction of Spermiation in Sterlet Acipenser ruthenus by PLGA Microparticle Delivery with Sustained Alarelin Release.

Carp pituitary treatment versus poly (lactiac-co-glycolic acid) microparticles with slow release of Alarelin at 35 µg kg-1 or 200 µg kg-1 body weight to induce spermiation was compared in sterlet Acipenser ruthenus. All hormone treatments initially increased testosterone and 11-ketotestosterone, with a subsequent decline in testosterone but consistent high levels of 11-ketotestosterone at 48 and 72 h post-treatment. Spermiation did not differ between hormone-treated groups, and was not detected in controls receiving saline solution. Administration of the carp pituitary led to maximum sperm production 24 h post-treatment, followed by a decrease at 48 h post-treatment, with no sperm obtained at 72 h. The effect of Alarelin at 35 µg kg-1 bw and carp pituitary did not differ at 24 and 48 h post-treatment, whereas 200 µg kg-1 bw Alarelin was associated with significantly lower spermatozoon concentration 24 h post-treatment compared to carp pituitary, with no difference in milt volume. Higher relative sperm production was observed 48 h after injection of Alarelin at 200 µg kg-1 bw compared to carp pituitary. Spermatozoon motility was significantly higher in fish receiving Alarelin at 35 µg kg-1 bw than 200 µg kg-1 bw. The treatment with optimal effect on inducing spermiation was poly (lactic-co-glycolic acid) microparticles with slow release of Alarelin at 35 µg kg-1 bw.