Ionic composition and osmolality of paddlefish (Polyodon spathula, Acipenseriformes) seminal fluid

Changes in ionic composition as Na⁺,K⁺, Ca²⁺ and Mg²⁺, osmolality inseminal fluid, percentage of motile spermatozoaand velocity were investigated in response toCPP and different dosage of LHRHa. The lowestvelocity of sperm was observed after use CPPtreatment. The velocity of spermatozoa,significant main effect of the treatment(P < 0.0001) and the time of sperm collection(P < 0.0104) were evaluated. The osmolality ofseminal fluid was different betweenexperimental groups of LHRHa (48.0–62.7mOsmol.kg^–1) and CPP (33.0–46.3mOsmol.kg^–1) treatments. The osmolalitywas significantly higher on the first day andone-half, then declined on day three, rangingfrom 33.0 to 62.7 mOsmol.kg^–1. Analysisof variance showed significant main effects ofthe treatment (P < 0.0001) and the time ofsperm collection (P < 0.0002) on the osmolalityof seminal fluid. The level of Na⁺ andK⁺ ion was different between experimentalgroups of LHRHa and CPP treatment. The highestconcentration of 11.11 mmol.l^–1 wasobserved at Na⁺ ion. Then theconcentrations declined on the level 1.56, 0.52and 0.36 mmol.l^–1 for K⁺, Ca²⁺and Mg²⁺ ions, respectively. There werehighly positive correlations between osmolalityof seminal fluid and dosage of LHRHa treatment(r = 0.84), velocity of spermatozoa andosmolality of seminal fluid (r = 0.57) andosmolality of seminal fluid and Na⁺concentration at seminal fluid (r = 0.70).Injection with LHRHa increased quality of spermas velocity of sperm, level of Na⁺,K⁺ and osmolality at seminal fluidcompared to CPP treatments.     

The effect of K+, Ca2+, and Mg2+ on sperm motility in the perch,Perca fluviatilis

This study investigated the effect of 0.25–5 mM K⁺, Ca²⁺, and Mg²⁺ on sperm motility in the perch, Perca fluviatilis. In 75 mM NaCl, the used motility-activating solution, motility rate, and swimming velocity decreased within the first 4 min after activation, and the rate of locally motile sperm increased. Thereafter, the motility parameters remained constant for periods >20 min. Based on the decrease in sperm motility, two types of semen samples could be distinguished. Semen samples of type I retained a high motility rate of >65 % after 20 min, and the rate of locally motile sperm was <20 %. In semen samples of type II, the motility rate decreased to values <30 % after 20 min, and the rate of locally motile sperm exceeded >50 %. Ca²⁺ and Mg²⁺ concentrations of 0.25–0.5 mM had no effect on the sperm motility parameters 10 s after activation, while 0.25 mM K⁺ increased the swimming velocity. K⁺, Ca²⁺, and Mg²⁺ concentrations ≥1.5 mM had suppressive effects on the sperm motility 10 s after activation. No differences were found between the two semen types. Twenty minutes after activation, type I semen was not affected by the tested cations. On the contrary, 0.25–2.5 mM K⁺, 0.25 mM Mg²⁺, and 0.25–2.5 mM Ca²⁺ significantly increased the sperm motility rate and/or sperm velocity of type II semen. Therefore, supplementation of saline solution with cations might stabilize the motility of perch sperm, which can be a benefit for experimental purposes and for specific handling procedures in aquaculture.     

Changes in Sperm Production,Sperm Motility,and Composition of Seminal Fluid in Caspian Brown Trout,Salmo trutta caspius,Over the Course of a Spawning Season

This study was carried out to evaluate milt quality in male Caspian brown trout (Salmo trutta caspius) over the course of the winter spawning season. Milt samples were collected biweekly during December and January. Chemical composition of seminal fluid, sperm production (milt volume, sperm density, spermatocrit,) and sperm motility characteristics (percentage and duration of motility) were measured. Milt volume, sperm density, osmolality, seminal minerals (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^?), and total protein gradually decreased over the spawning season. Glucose and triglyceride content of milt did not show significant changes over the spawning season. Milt pH and the percentage and duration of motility were comparatively stable, declining only at the end of the season. Significant positive correlations were found between sperm density and seminal minerals, total protein and spermatocrit; percentage of motile spermatozoa and seminal minerals, total protein; and duration of motility and K⁺, Cl^?, total protein, and pH. Results show that season has a significant influence on milt quality in male Caspian brown trout, with the best milt being available at the beginning of spawning season.     

Sperm motility and fertilizing ability in the Persian sturgeon Acipenser persicus

The motility and fertilizing ability of the Persian sturgeon, Acipenser persicus, spermatozoa were investigated. Optimum ionic content (Na⁺, K⁺, Ca²⁺ and Mg²⁺) and pH of activation solution as well as the optimum dilution rate were determined. The results show optimum motility characteristics of spermatozoa in buffered solutions containing 25, 0.2, 3 and 10 mM L^?1 Na⁺, K⁺, Ca²⁺ and Mg²⁺, respectively, at dilution rate 1:50 and pH 8.0. To test the fertilizing ability of sperm, two buffered saline solutions were used as activation solution of sperm motility. The present study indicated (1) spermatozoa motility is one of key factors that influence on fertilizing ability of sperm, (2) a high fertilizing ability of sperm is obtained after dilution in saline solutions rather than in freshwater and (3) a maximum fertilization rate occurs in buffered saline solution containing 0.2 mM L^?1 K⁺. There is also a good correlation between biochemical characteristics of seminal plasma and fertilizing ability of sperm.     

Effect of different methods for the induction of spermiation on semen quality in European eel

Five hormonal treatments with human chorionic gonadotropin (hCG) were tested for the induction of maturation and spermiation in male farmed eels. The main aim was to optimize previously used hormonal treatments to achieve shorter induction treatments, longer spermiation periods and/or higher sperm quality. Fish treated for just 3 weeks (treatment E) or until the onset of spermiation (treatment C) showed the worst results, while the treatment consisting of weekly administration of 1.5 IU hCG g^?1 fish (treatment A) induced the highest percentage of spermiating males, the highest number of sperm samples and sperm volumes and densities similar to the rest of the treatments (B: half hormone dosage, or D: biweekly administration). Evaluation of the sperm quality was performed by computer‐assisted sperm analysis (CASA), considering the percentage of total motile spermatozoa, the percentage of fast and medium‐velocity spermatozoa, as well as different motility parameters. Sperm samples from A‐D groups showed between 44% and 54% motile spermatozoa, and between 10% and 15% fast spermatozoa, while samples from E‐treated males showed 0% motile cells. No significant differences were found in the spermatozoa straight line velocity (VSL), curvilinear velocity (VCL) or the angular velocity (VAP), neither spermatozoa beating cross frequency (BCF) between A–D groups.     

Sperm motility and seminal plasma characteristics in Barbus sharpeyi (Günther, 1874)

Spermatozoa concentration, ionic composition, osmolality, glucose and total protein contents of seminal plasma and sperm motility were determined in Barbus sharpeyi (Cyprinidae, Teleosotei). Spermatozoa concentration ranged from 9.77 to 20.20 × 10⁹ spermatozoa mL^?1. Osmolality (mOsmol kg^?1) and ionic contents (mM L^?1) of the seminal plasma were 274.5±9.0, 70.0±3.4 Na⁺, 28.8±0.9 K⁺, 101.7±3.1 Cl^?, 0.9±0.1 Mg²⁺ and 2.1±0.1 Ca²⁺ respectively. Total protein and glucose were 5.3±0.2 g L^?1 and 76.7±4.3 mM L^?1 respectively. Sperm motility was initiated in a hypo‐osmotic condition, composed of either an ionic (KCl or NaCl) or a non‐ionic (sucrose) activation medium. Duration of sperm motility was very short: <2 min after activation in distilled water. Percentage of motile spermatozoa was significantly higher in an activation medium containing NaCl compared with that of distilled water. An activating medium containing NaCl or KCl higher than 150 mM or sucrose higher than 275 mM totally inhibited the activation of sperm motility. Immediately after sperm activation, wave(s) propagated along the flagellum, but waves were restricted to the proximal part of the flagellum (close to the head) at 1 min post activation. Studied characteristics in the present study were compared with those of other cyprinids for understanding inter‐species differences.     

Motility of spermatozoa ofAlburnus alburnus (Cyprinidae) and its relationship to seminal plasma composition and sperm metabolism

The composition of seminal plasma and metabolism of sperm of the cyprinid fishAlburnus alburnus were investigated. Statistically significant correlations were found between motility parameters and seminal fluid osmolality, pH, Na⁺, K⁺ and protein levels (negative correlations: % immotile spermatozoa-Na⁺, K⁺; positive correlations: % motile spermatozoa-osmolality, pH, Na⁺, K⁺, protein; % linear motile spermatozoa-pH protein; swimming velocity of spermatozoa-pH, Na⁺, protein). Spermatozoan motility and ATP metabolism and glycolysis were correlated as indicated by measurement of ATPase, pyruvate kinase, adenylate kinase and lactate dehydrogenase activity. The physiological meanings of these correlations and their possible significance for quality control of semen are discussed.Abbreviations used ACP acid phosphatase - ADP adenosine diphosphate - AK adenylate kinase - ALP alkaline phosphatase - ASPAT aspartate aminotransferase - ATP adenosine triphosphate - ATPase magnesium dependent adenosine triphosphatase - CRPO creatine phosphate - -GLU \-D-glucuronidase - ICDH isocitrate dehydrogenase - LDH lactate dehydrogenase - PK pyruvate kinase     

Studies on sperm of diploid and triploid tench, Tinca tinca (L.)

The tench Tinca tinca is an interesting fish from the viewpoint of polyploidy and related atypical reproduction aspects. Triploid tench were produced artificially. Studies of spermiation as well as of sperm motility and structure were performed on several triploid and diploid males simultaneously with individual experimental crosses with diploid females to define their reproductive capacities. The testes of triploids visually looked less developed in the most of cases with lower sperm production (0.05 cm³ sperm per male), GSI and weight of testes compared to diploids (0.58 cm³ sperm per male). Analysis of variance showed significant influence of ploidy level on the percentage of motile spermatozoa. Triploidy did not change percentage of live spermatozoa and velocity of spermatozoa at the first time of sperm movement. The study of sperm structure by scanning electron microscopy revealed that most sperm cells were of normal structure with some anomalies. Sperm heads of triploid and diploid males were mostly round-shaped, 1.86±0.2 and 1.6±0.18 μm in diameter. The midpiece of triploid spermatozoa was slightly narrower than that of diploid ones with typical cylindrical shape. Flow cytometry revealed sperm cells of triploids to be largely aneuploid (1.47 n) with high mosaic DNA, oscillating from haploid DNA content (1.0 n) to diploid DNA content (1.9 n). Experimental crosses between triploid males and diploid females revealed that these males were capable to stimulate effective development with relatively high level of fertilization and hatching rates from 0 to 70%. In conclusion, triploidization does not seem to guarantee sterility of tench.     

Sperm of feral carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis>: optimization of activation solution

The spermatozoa of oviparous fish, such as feral carp (Cyprinus carpio), are immotile in the presence of semen plasma or isotonic solutions, and to obtain good motility, they must be diluted with suitable medium. The objective of this study was to identify the best activating solution for feral carp sperm. Sperm motilities were compared in the new activating solution (a): (50 mM NaCl, 30 mM KCl, 30 mM Tris, pH = 8.5) and activating solution (b): (50 mM NaCl, 40 mM KCl, 30 mM Tris, pH = 8.5) based on effect of pH with everyone of Na⁺ and K⁺ ions versus four other activating solutions Billard’s saline solution, Poupard’s saline solution, distilled water and hatchery water that is routinely used for extending carp semen. Our results showed that maximum total motility period and percentage of motile sperm were seen in selected saline solution (a). The present study describes an activating solution that prolongs feral carp sperm motility.     

Semen biology and stimulation of milt production in the European smelt (Osmerus eperlanus L.)

Basic characteristics of the European smelt (Osmerus eperlanus) sperm are reported here for the first time. Smelt spermatozoa had a bullet-shaped head (1.42 μm length), a short midpiece and a long flagellum (27.72 μm). Two mitochondria were located along the flagella. The volume of smelt sperm was small (30-60 μl) and the duration of sperm motility was short (22 s in distilled water and 41 s in 20 mM sodium bicarbonate solution). Sodium chloride at concentrations ranging from 0-120 mM did not influence the percentage of motile spermatozoa but caused a steady increase in the duration of sperm movement. Potassium ions clearly reduced the percentage of motile sperm at a concentration of 10 mM. Spermatozoa were motile through a broad range of pH with an optimum from 7.5 to 8.5. Testicular spermatozoa had a different motility pattern compared to stripped spermatozoa (the latter exhibiting a reduction of motile spermatozoa by 30%, lower ALH and VCL and higher LIN and VSL). These results indicate that maturation of smelt spermatozoa occurring in sperm ducts is related not only to an increase of the percentage of motile spermatozoa but also to changes in the sperm motility pattern. Maintaining males with females resulted in stimulation of milt production. Our results indicate that European smelt sperm characteristics are similar to those of ayu (Osmeridae).     

Spermatozoon ultrastructure and sperm cryopreservation of the Brazilian dry season spawner fish pirapitinga,Brycon nattereri

The aims of this study were to describe the fresh spermatozoon ultrastructure using scanning and transmission electron microscopy and to improve the sperm cryopreservation methodology for the freshwater fish pirapitinga Brycon nattereri. Extenders (BTS^? and NaCl), straw volumes (0.5 and 4.0 mL), thawing temperatures (30 and 60 °C) and activating agents (0.29% NaCl and 1% NaHCO₃) were tested. Methylglycol was used as a cryoprotectant agent and sperm was frozen in nitrogen vapour (dry‐shipper). Post‐thawed sperm motility rate, motility quality (score 0=no movement; 5=rapidly swimming spermatozoa), duration of motility and spermatozoon morphology were evaluated. Fresh spermatozoon was 35.06 μm long, the head was ovoid (2.00 × 1.22 μm) with no acrosome, the midpiece was 2.15 μm long and the flagellum was 30.90 μm long with the typical 9+2 axoneme arrangement. Post‐thawed sperm motility rate (70–79% motile sperm), motility quality (score 3.1–3.7) and morphology (9.3–11.6% abnormal spermatozoa) were not affected by any of the parameters tested. The duration of sperm motility was longer when triggered in 1% NaHCO₃ (392–1031 s) compared with 0.29% NaCl (144–338 s). Brycon nattereri sperm cryopreserved under the conditions described above yields over 70% motility and should last long enough to fertilize oocytes, even after 2 years of freezing.     

Quantity, motility and fertility of tench Tinca tinca (L.) sperm in relation to LHRH analogue and carp pituitary treatments

The spermiation of tench males was stimulated with Supergestran containing mammalian LHRHa lecireline at the following doses: 5, 10, 20 and 40 g kg⁻¹ b.w.; then with carp pituitary suspension (CPS) at a dose of 2 mg kg⁻¹ b.w. and with a control of saline physiological solution. The following days, meaning 24, 48 and 72 h after injection, sperm was collected to evaluate volume and the number of sperm per male per kg body weight (B.W.) The percentage of motile sperm and velocity of spermatozoa were measured 48 h after hormonal injection, and 72 h after hormonal injection the sperm was evaluated for fertilization and hatching ability. All 42 males in experimental groups were diploid. Live weight did not differ significantly among experimental groups. The strongest stimulation of spermiation was achieved with LHRHa in dosage of 20 and 40 g kg⁻¹ b.w. and CPS compared to males of the control group and lower dosage of LHRHa. Analysis of variance showed no significant influence of the treatment on the velocity and percentage of motile spermatozoa. The effect of different treatment on the fertilization capacity (the number of spermatozoa per egg was equilibrated) was significant. Significantly the highest quality of sperm collected 72 h after injection expressed by percentage of fertilization and hatching (62–65% fertilization and 61–64% hatching rates, respectively) was found for LHRHa in dosage of 20 and 40 g kg⁻¹ b.w. Significantly the lowest parameters of fertilization and hatching were found for the control group, on the 12% level.     

Cryopreservation of Sperm of Farmed European Eel Anguilla anguilla

Sexual maturation and sperm release were induced in farmed European eels Anguilla anguilla kept exclusively in fresh water by using two dosages of human chorion gonadotropin (100 International Unit (IU)-Group one and 250 IU/individual per week-Group two). Sperm release took over 13 wk in both groups. The quality of sperm was investigated on the eighth, ninth, and tenth wk. The average cell densities were 0.94 ± 0.4 × 1010 (Group one) and 0.93 to. ± 0.6 × 10¹⁰ (Group two) spermatozoa/mL. The estimated motility of eel sperm was 33, 55, and 49% on the eighth, ninth, and tenth wk of treatment, respectively. The estimated average motility of samples selected for cryopreservation was 73 ± 10%, while the post-thaw motility of cryopreserved samples was 36 ± 11%. The extender originally developed for common carp sperm crypreservation together with methanol as cryoprotectant was found suitable for the cryopreservation of European eel sperm.     

Retention of sperm motility in turbot, Scophthalmus maximus L.: the effects of time from activation, thermal shock and adenosine triphosphate levels

Abstract Four parameters were examined in order to define sperm quality in turbot Scophthalmus maximus L., sperm: (1) sperm motility, measured by direct counts of the number of active spermatozoa, expressed as % of total spermatozoa; (2) retention of motility after activation, measured by direct counts, 0–60min after activation, expressed as a % of the initial level of activity; (3) resistance to thermal stress, measured as change in retention of motility, and (4) adenosine phosphate (ATP) concentration, determined for samples of non-activated sperm. The proportion of motile spermatozoa at activation ranged from 34·8% to 97·6% (mean 76·3%) for the individual males tested. Turbot sperm retained on average 52% (range 27–90%) of its initial activity one hour after activation. Sperm samples which were stressed by cooling to –27°C retained only 8·6% (range 0–25%) of initial activity, compared to control samples which retained 49% (range 38–63%) of initial activity. The retention of motility after activation was not significantly related to the initial motility or the levels of ATP. Concentrations of ATP in turbot sperm (mean 0·46mg ATP/10⁶ spermatozoa, equivalent to 9·2nmol ATP/10⁸ spermatozoa) were comparable to those measured in mammals.     

Sperm quality of Brazilian flounder Paralichthys orbignyanus throughout the reproductive season

The aim of this study was to evaluate the sperm quality of Brazilian flounder Paralichthys orbignyanus throughout its reproductive season. Sperm was collected at the beginning, middle and end of the breeding period. Spermatozoa density was maximum at the beginning (12.7 ± 0.92 × 10⁹ cells mL^?1) and at the end (11.8 ± 0.39 × 10⁹ cells mL^?1) of the breeding season (P<0.05). Sperm production and the percentage of spermatozoa moving fast forward increased significantly towards the end of the breeding season (P<0.05). The mean duration of progressive motility of spermatozoa was around 10 min. No difference was observed during the reproductive season in the percentage of motile cells, pH, osmolality and K⁺, Cl^? and Mg²⁺ concentrations in seminal plasma. The concentration of Na⁺ increased throughout the breeding season, reaching 174.62 ± 12.68 mmol L^?1 at the end (P<0.05). There was a decline in the concentration of Ca²⁺ (12.31 ± 3.08 mmol L^?1) in the middle of the breeding season, which coincided with the shortest motility duration of spermatozoa. The information reported in this study should help to improve management and optimize the development of protocols for short‐term storage and cryopreservation of Brazilian flounder semen.     

Semen biology of vendace (<Emphasis Type="Italic">Coregonus albula</Emphasis> L.)

The objective of this study was to describe the morphometry and motility parameters of vendace (Coregonus albula) spermatozoa. Morphometric parameters of vendace sperm head and tail were of values similar to rainbow trout. The effects of pH, sodium, potassium and calcium ion concentrations on computer-assisted sperm analysis (CASA) sperm motility characteristics were tested. Vendace sperm was motile in a wide pH range of 6.0–10.5 with the optimum pH established at 9.0. Increases in potassium and calcium ions caused decreases in the percentage of motile sperm. The CASA parameters and erratic sperm movement pattern of vendace spermatozoa were similar to whitefish (C. lavaretus) sperm motility, suggesting that there is a coregonid-specific sperm motility pattern.     

Pre-spawning water temperature affects sperm respiration and reactivation parameters in male carps

Concentration, ability to motility, motility during the second activation (reactivation), and endogenous respiration were studied in sperm from two experimental groups of carp males. Group 1 was maintained for 7 days at 15°C (cold water (CW) group), whereas the second group was subjected to a temperature of 20°C (warm water (WW) group) before sperm sampling. Reactivation were achieved after incubation of firstly activated sperm in media with osmotic pressure adjusted up to 300 mOsm*kg⁻¹ by increasing K⁺ concentration. Statistically significant reduction of spermatozoa concentration in CW samples versus WW (from 46.0 ± 12.5 (15°C) to 59.3 ± 7 10⁹ (20°C) spermatozoa /ml) have been observed. The sperm of the CW group required a significantly longer incubation time (37 min) under isotonic conditions to achieve a maximum percentage of potent motility at repeated activation than the WW group (23 min). After activation of sperm motility, an increase of respiration rate up to maximum level has been found, this level remained the same under condition of recovering the potential to repeated activation. During the sperm movement respiration rate, in CW group (6.1 nmolO₂/min/10⁹spermatozoa) and WW (3.9 nmolO₂/min/10⁹spermatozoa), was significant higher compared to nonactivated sperm (2.4 nmolO₂/min/10⁹spermatozoa for CW and 1.1 nmolO₂ /min/10⁹spermatozoa for WW). And keeping males for 7 days at 15°C increase the respiration rate of sperm.     

Sperm quality in male <Emphasis Type="Italic">Barbus barbus</Emphasis> L. fed different diets during the spawning season

Sperm quality of Barbus barbus L. was compared among the three following dietary regimes: Group A, fed 100% commercial diet (Karpico™ containing 33% crude protein and 6% fat), Group B, fed 78% commercial diet and 22% frozen chironomid (Chironomus plumosus) larvae, and Group C, fed 56% commercial diet and 44% frozen chironomid larvae. Concentrations of polyunsaturated fatty acids (PUFAs) in Group A, B, and C were 39.1, 42.0, and 44.6, respectively, as a percentage of total fatty acids. Sperm morphology, volume, concentration and motility, total number of spermatozoa, and osmolality of the seminal plasma were compared during the spawning season. Dietary regime did not influence sperm volume, concentration, or total number of spermatozoa, osmolality of seminal plasma, or the percentage of motile sperm, but significantly affected sperm morphology (except for anterior and posterior parts of the midpiece) and sperm velocity (P < 0.05). Groups B and C showed similar sperm characteristics during the spawning season compared to Group A. Almost all parameters changed either among or within groups during the spawning season, suggesting differences in terms of the optimal time for sperm collection. The best time for sperm collection was March for Group A, but April for Groups B and C, when the osmolality of the seminal plasma measured 289 mOsmol kg⁻¹ and sperm motility was maximal. Spermatogenesis, hydration, and cell decomposition were confirmed as the three major parameters controlling sperm characteristics during the spawning season. The possible correlation between sperm morphology and motility requires further study.     

Changes of sperm morphology,volume, density,and motility parameters in northern pike during the spawning period

Sexually mature males (BW?=?1600?±?150 g and TL?=?235?±?30 mm) of northern pike (Esox lucius L.) were randomly selected from a pond to record changes in their sperm quality parameters (spermatozoa morphology, sperm volume, density, and motility parameters) during the spawning season. The morphological and motility parameters changed significantly during the reproductive season with following trends. Only, head width was not changed during the spawning season. The longest spermatozoa and its flagellar length were found at the middle of spawning period (TL?=?38.24?±?0.37 μm and 35.14?±?0.26 μm) and shortest at the beginning of spawning period (TL?=?34.81?±?0.29 μm and 32.53?±?0.18 μm). Other morphological characters were always the lowest at the beginning of spawning period. Sperm volume was changed from 0.33?±?0.3 ml in February, 0.43?±?0.2 ml in March to 0.24?±?0.1 ml in April, and density from 16.2?±?0.2?×?109 spermatozoa ml^?1 in February, 19.4?±?0.2?×?109 spermatozoa ml^?1 in March to 4.8?±?0.2?×?109 spermatozoa ml^?1 in April. Same sperm velocity was observed in all spawning terms at 10 and 20 s after activation. Higher velocity was found at 30 and 40 s after activation in sperm collected at the middle and the end of spawning period. Significantly, higher percentage of motile sperm was observed at 20, 30, and 40 s after activation in sperm sampled at the end of spawning period. This study supports the hypothesis that longer spermatozoa swim faster.     

Induced spermiation in 3-year-old sterlet, Acipenser ruthenus L.

Spermiation in 3‐year‐old sterlet, Acipenser ruthenus (L.), males maintained under warm water conditions was induced by intramuscular injection of either (i) (D‐Ala⁶)‐GnRH‐ProNHEt (Kobarelin); (ii) mammalian GnRH analogue+metoclopramide (Ovopel); or (iii) human chorionic gonadotropin (Biogonadyl). The volume of milt, sperm concentration and motility were measured. A higher percentage of spermiating males was obtained after Kobarelin or Ovopel treatment (81.8% and 77.7% respectively) in comparison with fish treated with Biogonadyl (40.0%). However, only stimulation with Ovopel guaranteed motile spermatozoa in all spermiating males. Moreover, treatment with Ovopel resulted in the highest average milt volume, sperm concentration and motility. The average total number of motile spermatozoa (milt volume×sperm concentration×sperm motility) per individual was 0.99×10⁹, 5.31×10⁹ and 0.02×10⁹ after stimulation with Kobarelin, Ovopel or Biogonadyl respectively. Our data indicate that Ovopel is a good stimulator of spermation in sturgeons. Moreover, the time of sexual maturation could be significantly reduced in sturgeons maintained in cages under warm water conditions.