Comparison of two techniques for the morphometry study on gilthead seabream (Sparus aurata) spermatozoa and evaluation of changes induced by cryopreservation

The development of powerful software has made possible spermatozoa morphology studies. However, some problems have emerged in relation to protocol standardization to compare results from different laboratories. This study was carried out to compare two techniques commonly used (staining vs phase contrast technique) for the morphometry study of gilthead sea bream spermatozoa using an integrated sperm analysis system (ISAS). Spermatozoa morphometry values were significantly affected by the technique used, and phase contrast technique was found to be the more accurate method, showing lower coefficients of variation on spermatozoa morphometry parameters measurements. Moreover, it has been shown that cryopreservation process produces damage in gilthead sea bream spermatozoa, causing negative effects in sperm parameters as spermatozoa morphometry (a decrease in cell volume), motility (from 95 to 68% motile cells) and viability (from 95 to 87% of live cells), being the addition of freezing medium containing cryoprotectant (DMSO) an important factor that caused the morphometry changes.     

Sperm cryopreservation of green swordtail Xiphophorus helleri, a fish with internal fertilization

Sperm cryopreservation for fishes with internal fertilization is essentially unexplored although many species of these fishes are valuable biomedical research models. To explore methods for sperm cryopreservation within the live-bearing genus Xiphophorus, this study used X. helleri to evaluate the effects of cryoprotectant, osmotic pressure, cooling rate, equilibration time, and sperm-to-extender ratio. Sperm motility and survival duration after thawing showed significant differences among different cryoprotectants with the highest motility at 10 min after thawing obtained with 14% glycerol. With subsequent use of 14% glycerol as the cryoprotectant, the highest motility after thawing was observed with Hanks' balanced salt solution (HBSS) at 300 mOsmol/kg. Samples cooled from 5 to -80 degrees C at 20 degrees C/min yielded the highest post-thaw motility although no significant difference was found in the first 4h after thawing for cooling rates across the range of 20-35 degrees C/min. Evaluation of equilibration time revealed no significant difference between 20 min and 2h, but the highest motility at 10 min after thawing was found with a 20-min equilibration. Dilution ratios of sperm-to-extender at 1:20, 1:60, and 1:120 showed no significant differences in motility and survival duration after thawing, but the dilution of sperm solutions with HBSS (320 mOsmol/kg) immediately after thawing reduced the decline of sperm motility, and significantly prolonged the survival duration. Based on these findings, the highest average sperm motility (77%) at 10 min after thawing was obtained when sperm were suspended in HBSS at 300 mOsmol/kg with 14% glycerol as cryoprotectant, diluted at a ratio of sperm to HBSS-glycerol of 1:20, equilibrated for 10 min, cooled at 20 degrees C/min from 5 to -80 degrees C before being plunged in liquid nitrogen, and thawed in a 40 degrees C water bath for 7s. If diluted immediately after thawing, sperm frozen by the protocol above retained continuous motility after thawing for more than 8 days when stored at 4 degrees C.     

Effect of lactoferrin on ram sperm motility after cryopreservation

ObjectiveThe objective of this study was to analyse the differentially abundant proteins caused by freeze–thawing of ram sperm and explore candidate proteins of interest for their ability to improve ram sperm cryopreservation outcomes in vitro.MethodsSperm were from three mature Dorper. Fresh and frozen sperm proteins were extracted, and the differentially abundant proteins were analysed by mass spectrometry. Among these proteins, lactoferrin (LTF) was selected to be added before cryopreservation. Next, sperm samples were diluted in Tris extender, with the addition of 0, 10, 100, 500, and 1,000 μg/mL of LTF. After thawing, sperm quality was evaluated by motility, plasma membrane integrity, mitochondrial activity and reactive oxygen species (ROS).ResultsCryopreservation significantly altered the abundance of 40 proteins; the abundance of 16 proteins was increased, while that of 24 proteins was decreased. Next, LTF was added to Tris extender applied to ram sperm. The results showed that sperm motility and plasma membrane integrity were significantly improved (p<0.05) by supplementation with 10 μg/mL LTF compared to those in the control group. There was no significant difference in mitochondrial activity between the 0 μg/mL group and other groups (p>0.05). Supplementation of the cryoprotective extender with 10 μg/mL LTF led to decreased ROS levels compared with those in the control and other groups (p<0.05).ConclusionThe LTF is an important protein during cryopreservation, and the addition of 10 μg/mL LTF to a cryoprotective extender can significantly improve the function of frozen ram sperm.     

A sperm cryopreservation protocol for the loach Misgurnus anguillicaudatus and its applicability for other related species

The aim of the present study was to establish a protocol of sperm cryopreservation in Misgurnus anguillicaudatus and verify the applicability of the obtained protocol in other loach species. We evaluated the following parameters: inseminating dose, thawing temperatures (20, 25 and 30 °C for 10 s), extenders (loach or cyprinid extenders), internal cryoprotectants (dimethyl sulfoxide (DMSO), dimethylacetamide (DMA), glycerol (Gly), ethylene glycol (EG), and methanol (MeOH) at 0, 5, 10 and 15%), external cryoprotectants (bovine serum albumin 1 and 2%; sucrose 0.5 and 1%; glucose 0.5 and 1%; glycine 0.5 and 1%), activating solutions (distilled water, dechlorinated tap water, 25 mM NaCl and 50 mM NaCl), and hatchability of the eggs when fertilized with fresh or cryopreserved sperm. After the evaluation of these parameters, we optimized the cryopreservation using the following procedure: thawing temperature at 25 °C for 10 s; loach or cyprinid extenders; methanol at 10 or 15% as internal cryoprotectants; glycine 0.5% or bovine serum albumin 1% as external cryoprotectants and 50 mM NaCl for sperm activation. Using this procedure, the fertilizability of the post-thawed sperm was 47% in comparison to the fresh sperm, at the minimum inseminating dose (687.65 spermatozoa egg⁻¹ mL⁻¹). Based on this protocol, sperm from other loach species Lefua nikkonis, Misgurnus mizolepis and Barbatula toni were cryopreserved successfully.     

Commercial-scale sperm cryopreservation of diploid and tetraploid Pacific oysters, Crassostrea gigas

Cryopreservation of sperm from tetraploid organisms (the possession of four chromosome sets) is essentially unexplored. This is the first cryopreservation study to address sperm from tetraploid Pacific oysters, Crassostrea gigas, and addresses the commercial production of triploid oysters (three chromosome sets). Initial motility, refrigerated storage of undiluted sperm, osmolality of extender solutions, sperm concentrations, equilibration time, and cryoprotectants of propylene glycol and dimethyl sulfoxide were evaluated with sperm from diploid and tetraploid oysters. Unlike most teleost fishes, in which the duration of active motility is typically brief, the motility of sperm from oysters lasts for hours. The present study showed that responses to treatment effects by sperm from tetraploids were different from diploids. The majority of tetraploid experiments resulted in less than 10% motility after thawing and less than 5% fertilization. The highest fertilization obtained for thawed sperm was 96% for sperm from diploid oysters and 28% for sperm from tetraploid oysters. Differential responses to treatments by sperm from tetraploid and diploid oysters may be due to differences in gonadal development. However, the use of cryopreserved sperm from tetraploid Pacific oysters produced 100% triploid offspring by fertilization of eggs from diploid females as determined by flow cytometry of larvae. This study demonstrates that sperm from tetraploid oysters can be collected, frozen, and stored for production of triploid offspring.     

Effect of cryopreservation protocol on postthaw characteristics of stallion sperm

Three ejaculates from each of eight stallions were subjected to cryopreservation in a milk/egg yolk-based freezing extender or an egg yolk-based freezing extender. Semen was exposed to a fast prefreeze cooling rate (FAST; semen immediately subjected to cryopreservation) or a slow prefreeze cooling rate (SLOW; semen pre-cooled at a controlled rate for 80 min prior to cryopreservation). Postthaw semen was diluted in initial freezing medium (FM) or INRA 96 (IMV Technologies, L'Aigle, France) prior to analysis of 10 experimental end points: total motility (MOT; %), progressive motility (PMOT; %), curvilinear velocity (VCL; μm/s), linearity (LIN; %), intact acrosomal and plasma membranes (AIMI; %), intact acrosomal membranes (AI; %), intact plasma membranes (MI; %), and DNA quality. Eight of 10 experimental endpoints (MOT, PMOT, average-path velocity [VAP], mean straight-line velocity [VSL], LIN AIMI, AI, and MI) were affected by extender type, with egg yolk-based extender yielding higher values than milk/egg yolk-based extender (P < 0.05). Exposure of extended semen to a slow prefreeze cooling period resulted in increased values for six of eight endpoints (MOT, PMOT, VCL, AIMI, AI, and MI), as compared with a fast prefreeze cooling period (P < 0.05). As a postthaw diluent, INRA 96 yielded higher mean values than FM for MOT, PMOT, VCL, average-path velocity, and mean straight-line velocity (P < 0.05). Treatment group FM yielded slightly higher values than INRA 96 for LIN and MI (P < 0.05). In conclusion, a slow prefreeze cooling rate was superior to a fast prefreeze cooling rate, regardless of freezing extender used, and INRA 96 served as a satisfactory postthaw diluent prior to semen analysis.     

Effect of melatonin supplementation to a cytoprotective medium on post-thawed Brycon orbignyanus sperm quality preserved during different freezing times

The aim of the present study is to verify the viability of frozen B. orbignyanus sperm cells after freezing with dilution media containing different concentrations of the melatonin and after different freezing times. Semen from 15 males was collected and pooled as five pools from three random animals. Oocytes (100) from three females were separately used for fertilization. There were three treatments: (C) Control Medium: 90% of extender Beltsville thawing solution (5% concentration) + 10% methylglycol (MG); (M1) Control Medium + 1 mM melatonin; and (M2) Control Medium + 2 mM melatonin. Sperm samples were diluted in media at a final proportion of 1:4 [125 μl sperm (25% V/V) + 337.5 μl BTS (65% V/V) + 37.5 μl MG (10% V/V)]. Melatonin was added at final solution. Three Dry shipper freezing times were used: T1 (15 min), T2 (12 h) and T3 (24 h). The samples were transferred, stored in a cryobank and thawed in a water bath at 60 °C for 5 s and evaluated concerning viability, morphology and fertilization rate. B. orbignyanus semen frozen in M2 presented the highest fertilization rate (8.40 ± 2.54%). The highest vitality (85.2 ± 2.8%), motility (64.63 ± 8.3%), motility duration (84.22 ± 11.4 s) and progressive motility (17.01 ± 1.2%) rates were maintained for M2. The highest number of altered cells was observed in C (57.4 ± 5.9%). Melatonin at 2 mmol L⁻¹ associated with the cryoprotectant methylglycol in cryopreservation could be used to improve a cryobank for endangered Brycon orbignyanus populations.     

An evaluation of soybean lecithin as an alternative to avian egg yolk in the cryopreservation of fish sperm

Plant-derived lecithin has been used as a more sanitary alternative to avian egg yolk in livestock sperm cryopreservation protocols but its efficacy for cryopreserving fish sperm has not previously been tested comparatively. Here various concentrations of soybean lecithin were evaluated for the cryopreservation of carp (Cyprinus carpio) sperm. Sexually mature fish were induced to spermiation and ovulation with ovopel. The extenders were prepared by using 300 mM glucose, 10% DMSO, supplemented with different ratios of lecithin (5%, 10%, 15%, and 20%) and 10% egg yolk (control I). Negative control was made without egg yolk and soybean lecithin (control II). The pooled semen was diluted separately at ratio of 1:3 (v/v) by using egg yolk and soybean-based extenders. Diluted semen placed into 0.25 ml straws were equilibrated at 4 °C for 15 min and frozen in liquid nitrogen vapor. Fertilization was conducted using a ratio of 1 × 10⁵ spermatozoa/egg. Supplementation of 10% lecithin to extender showed the best cryoprotective effect for sperm motility and duration of motility against freezing damage compared to 15%, 20% and control II groups (p < 0.05). Cryopreserved sperm with extender containing 10% lecithin provided a greater result in terms of fertilization success when compared to extenders containing 20% lecithin or control II (p < 0.05).     

Cryopreservation of red snapper (Lutjanus argentimaculatus) sperm: Effect of cryoprotectants and cooling rates on sperm motility, sperm viability, and fertilization capacity

Sperm cryopreservation of red snapper (Lutjanus argentimaculatus) is essentially unexplored, although many species of the Lutjanidae family are considered to be high-value commercial species. The objective of this study was to develop a species-specific cryopreservation protocol for red snapper (L. argentimaculatus) sperm by optimizing cryoprotectants and cooling rates in the cryopreservation procedure. Ten cryoprotectants at four concentrations and two freezing protocols were examined in two separate experiments. In the first experiment, toxicity studies of dimethyl sulfoxide (DMSO), glycerol, propylene glycol (PG), ethylene glycol (EG), formamide, methanol, ethanol, sucrose, trehalose, and dimethylacetamide (DMA) on sperm motility were performed. Semen diluted 1:1 in Ringer solution were exposed to cryoprotectants at four final concentrations of 5%, 10%, 15%, or 20% for periods of 10, 20, 30, 40, 50, 60, 90, and 120 min at room temperature (25 °C). The cryoprotectants and concentrations that showed the least toxic effect on sperm motility were selected for cryopreservation trials. In the second experiment, selected cryoprotectants were then assessed for freezing capacity of sperm as follows: DMSO 5% and 10%, PG 5% and 10%, EG 5% and 10%, ethanol 5%, and methanol 5%. Semen was diluted 1:1 in Ringer solution and equilibrated with selected cryoprotectants for 10 min at room temperature. Sperm were frozen in a controlled-rate programmable freezer at four cooling rates of 3, 5, 10, and 12 °C/min from an initial temperature of 25 °C to final temperatures of −40 or −80 °C before plunging into liquid nitrogen. Sperm equilibrated in 10% DMSO and cooled at a rate of 10 °C/min to a final temperature of −80 °C had the highest motility (91.1 ± 2.2%) and viability (92.7 ± 2.3%) after thawing. The fertilization rate of frozen-thawed sperm (72.4 ± 2.4%) was not different (P > 0.05) from that of fresh sperm (75.5 ± 2.4%). This study apparently represents the first reported attempt for cryopreservation of L. argentimaculatus sperm.     

Control of sperm concentration is necessary for standardization of sperm cryopreservation in aquatic species: evidence from sperm agglutination in oysters

A lack of standardization in sperm cryopreservation of aquatic organisms is one of the main reasons for inconsistency observed among various studies. In particular, there have been few attempts to standardize sperm concentration during procedural optimization. This study was intended to call attention to sperm concentration standardization through research of sperm agglutination in Pacific oysters Crassostrea gigas. Sperm agglutination after thawing is a relatively frequent phenomenon observed for various aquatic species, especially when sub-optimal cryopreservation protocols are used; however, no systematic attempts have been made to explain this phenomenon. The present study evaluated various factors affecting sperm agglutination of thawed samples from diploid and tetraploid Pacific oysters, and is the first detailed report addressing the sperm agglutination phenomenon of thawed samples from any aquatic organism. Agglutination of oyster sperm was classified into six levels with a scale ranging from 0 (homogenous suspension) to 5 (well-developed "noodles"). It was found that agglutination in thawed samples was mainly due to the lack of sufficient cryoprotectant for a specific sperm concentration. Interestingly, high levels of agglutination did not necessarily lead to low fertilization. On the contrary, some sperm cells appeared to gain protection from the formation of peripheral agglutination within 0.5-ml French straws. The exact mechanism of sperm agglutination remains unclear. However, morphological examination of cross sections of the noodles (agglutination level 5) indicated at least two forms of agglutination (formed with and without cryoprotectant) which could be used as a tool to understand the cryopreservation process within the micro-environment of the straw. Furthermore, the fact that the level of sperm agglutination was directly determined by sperm concentration, in addition to the type of cryoprotectant, cryoprotectant concentration, and cooling and thawing methods emphasized the importance of procedural standardization and systematic optimization and integration of protocols involving multiple factors.     

Recovery and cryopreservation of epididymal sperm from agouti (Dasiprocta aguti) using powdered coconut water (ACP-109c) and Tris extenders

The objective was to compare the use of powdered coconut water (ACP-109c; ACP Biotecnologia, Fortaleza, CE, Brazil) and Tris extenders for recovery and cryopreservation of epididymal sperm from agouti. The caudae epididymus and proximal ductus deferens from 10 sexually mature agoutis were subjected to retrograde washing using ACP-109c (ACP Biotecnologia) or Tris. Epididymal sperm were evaluated for motility, vigor, sperm viability, membrane integrity, and morphology. Samples were centrifuged, and extended in the same diluents plus egg yolk (20%) and glycerol (6%), frozen in liquid nitrogen, and subsequently thawed at 37°C for 1 min, followed by re-evaluation of sperm characteristics. The two extenders were similarly efficient for epididymal recovery, with regard to the number and quality of sperm recovered. However, for both extenders, sperm quality decreased (P < 0.05) after centrifugation and dilution. After sperm cryopreservation and thawing, there were (mean ± SEM) 26.5 ± 2.6% motile sperm with 2.6 ± 0.2 vigor in the ACP-109c (ACP Biotecnologia) group, which was significantly better than 9.7 ± 2.6% motile sperm with 1.2 ± 0.3 vigor in Tris. In conclusion, agouti epididymal sperm were successfully recovered using either ACP-109c (ACP Biotecnologia) or Tris extenders; however, ACP-109c (ACP Biotecnologia) was a significantly better extender for processing and cryopreserving these sperm.     

Novel methylation at GpC dinucleotide in the fish Sparus aurata genome

To date, vertebrate DNA has been found methylated at the 5 position of cytosine exclusively in dinucleotide CpG or CpNpG stretches. On the the other hand, we determined that cytosine was methylated unusually in dinucleotide GpC at 5-GGCC-3 sequences in the teleost Sparus aurata EcoRI satellite DNA family. This finding is the first example of methylated GpC sequences in the eukaryotic genomes. At this regard, we have examined the relative methylation levels at this site of the highly repetitive EcoRI satellite DNA family from Sparus aurata different tissues. The EcoRI repeat was remarkably more methylated in male germ cells but hypomethylated in female germ cells at the Hae III restriction site ( GpC). The novel modification and the differential methylation pattern suggest that EcoRI satellite could have a structural and/or functional role at the centromeres of Sparus aurata.     

Evaluation of cryoprotectant and cooling rate for sperm cryopreservation in the euryhaline fish medaka Oryzias latipes

Medaka Oryzias latipes is a well-recognized biomedical fish model because of advantageous features such as small body size, transparency of embryos, and established techniques for gene knockout and modification. The goal of this study was to evaluate two critical factors, cryoprotectant and cooling rate, for sperm cryopreservation in 0.25-ml French straws. The objectives were to: (1) evaluate the acute toxicity of methanol, 2-methoxyethanol (ME), dimethyl sulfoxide (Me₂SO), N,N-dimethylacetamide (DMA), N,N-dimethyl formamide (DMF), and glycerol with concentrations of 5%, 10%, and 15% for 60 min of incubation at 4 °C; (2) evaluate cooling rates from 5 to 25 °C/min for freezing and their interaction with cryoprotectants, and (3) test fertility of thawed sperm cryopreserved with selected cryoprotectants and associated cooling rates. Evaluation of cryoprotectant toxicity showed that methanol and ME (5% and 10%) did not change the sperm motility after 30 min; Me₂SO, DMA, and DMF (10% and 15%) and glycerol (5%, 10% and 15%) significantly decreased the motility of sperm within 1 min after mixing. Based on these results, methanol and ME were selected as cryoprotectants (10%) to evaluate with different cooling rates (from 5 to 25 °C/min) and were compared to Me₂SO and DMF (10%) (based on their use as cryoprotectants in previous publications). Post-thaw motility was affected by cryoprotectant, cooling rate, and their interaction (P ? 0.000). The highest post-thaw motility (50 ± 10%) was observed at a cooling rate of 10 °C/min with methanol as cryoprotectant. Comparable post-thaw motility (37 ± 12%) was obtained at a cooling rate of 15 °C/min with ME as cryoprotectant. With DMF, post-thaw motility at all cooling rates was ?10% which was significantly lower than that of methanol and ME. With Me₂SO, post-thaw motilities were less than 1% at all cooling rates, and significantly lower compared to the other three cryoprotectants (P ? 0.000). When sperm from individual males were cryopreserved with 10% methanol at a cooling rate of 10 °C/min and 10% ME with a rate of 15 °C/min, no difference was found in post-thaw motility. Fertility testing of thawed sperm cryopreserved with 10% methanol at a rate of 10 °C/min showed average hatching of 70 ± 30% which was comparable to that of fresh sperm (86 ± 15%). Overall, this study established a baseline for high-throughput sperm cryopreservation of medaka provides an outline for protocol standardization and use of automated processing equipment in the future.     

Effect of cryopreservation on phosphorylation state of proteins involved in sperm motility initiation in sea bream

We have previously demonstrated that in sea bream Sparus aurata motility initiation determined changes in the phosphorylation state of some proteins. This paper describes an investigation of the effect of a freezing-thawing procedure on the protein phosphorylation/dephosphorylation pattern. Proteins extracted from fresh and cryopreserved spermatozoa (before and after motility activation) were separated on SDS-PAGE, blotted on nitrocellulose membrane and treated with anti-phosphotyrosine, anti-phosphothreonine, or anti-phosphoserine antibodies. The results obtained demonstrate that the cryopreservation protocol has a strong effect on the phosphorylation state of proteins. In general, compared to fresh sperm, phosphorylated proteins are most numerous in both activated and non-activated cryopreserved sperm, and in particular we observed a dramatic increase in threonine phosphorylation. However, frozen-thawed sperm showed a minor number of proteins that changed their phosphorylation state after motility activation. Among these, we identified the acetyl-coenzyme A synthetase that plays a role in sperm motility initiation in both fresh and cryopreserved sperm.     

Sperm cryopreservation affects postthaw motility, but not embryogenesis or larval growth in the Brazilian fish Brycon insignis (Characiformes)

Sperm cryopreservation is an important method for preserving genetic information and facilitating artificial reproduction. The objective was to investigate whether the cryopreservation process affects postthaw sperm motility, embryogenesis, and larval growth in the fish Brycon insignis. Sperm was diluted in methyl glycol and Beltsville Thawing solution, frozen in a nitrogen vapor vessel (dry shipper) and stored in liquid nitrogen. Half of the samples were evaluated both subjectively (% of motile sperm and motility quality score—arbitrary grading system from 0 [no movement] to 5 [rapidly swimming sperm]) and in a computer-assisted sperm analyzer (CASA; percentage of motile sperm and velocity). The other half was used for fertilization and the evaluation of embryogenesis (cleavage and gastrula stages), hatching rate, percentage of larvae with normal development and larval growth up to 112 days posthatching (dph). Fresh sperm was analyzed subjectively (percentage of motile sperm and motility quality score) and used as the control. In the subjective analysis, sperm motility significantly decreased from 100% motile sperm and quality score of 5 in fresh sperm to 54% motile sperm and quality score of 3 after thawing. Under computer-assisted sperm analyzer evaluation, postthaw sperm had 67% motile sperm, 122 μm/sec of curvilinear velocity, 87 μm/sec of straight-line velocity and 103 μm/sec of average path velocity. There were no significant differences between progenies (pooled data) for the percentage of viable embryos in cleavage (62%) or gastrula stages (24%) or in the hatching rate (24%), percentage of normal hatched larvae (93%), larval body weight (39.8 g), or standard length (12.7 cm) at 112 days posthatching. Based on these findings, cryopreserved sperm can be used as a tool to restore the population of endangered species, such as B. insignis, as well as for aquaculture purposes, without any concern regarding quality of the offspring.     

Effects of type III antifreeze protein on sperm and embryo cryopreservation in rabbit

We investigated the effects of antifreeze protein (AFP) III supplementation on the cryopreservation of rabbit sperm cells and embryos. Ejaculated semen was collected from male Japanese white (JW) rabbits and divided into four AFP-supplemented groups (0.1 μg/ml, 1 μg/ml, 10 μg/ml, 100 μg/ml) and one control group with no AFP-supplementation. The semen samples were treated with egg-yolk HEPES extender containing 6% acetamide before the sperm was cooled from room temperature to 5 °C, then packed into sperm straws. The straws were frozen in steam of liquid nitrogen (LN₂) and then preserved in the LN₂. The motility of the sperm after thawing in 37 °C water was analyzed. The percentage of rapidly motile sperm in the 1 μg/ml AFP group was significantly higher than in the control group. Morulae were collected from female JW rabbits and divided into three AFP-supplemented groups (100 ng/ml, 500 ng/ml, 1000 ng/ml) and one control group. The morulae, immersed in an embryo-freezing solution (M199-HEPES containing 20% ethylene glycol, 20% dimethylsulfoxide, 10% fetal bovine serum and 0.25 M sucrose), were packed into open pulled embryo straws and vitrified in LN₂. The frozen embryos were thawed in the embryo-freezing solution, and the rates of embryo survival and development to blastocyte stage were analyzed after incubation for 72 h. The development rate of the embryos in the 500 ng/ml AFP group was significantly higher than in the control group, but that in the 1000 ng/ml AFP group was significantly lower. In conclusion, the appropriate dose of AFP III increased the number of rapidly motile sperm and embryo survival following freezing and thawing. The results suggest that supplementation with AFP III can increase the efficiency of cryopreservation of rabbit sperm cells and embryos.     

Spermatozoa concentration influences cryopreservation success in sea trout (Salmo trutta m. trutta L.)

Variation among individuals is substantial for spermatozoa concentration in fresh milt in sea trout (Salmo trutta m. trutta L.). The objective of the present study was to examine effects of spermatozoa concentration in this species on subsequent cryopreservation success. Milt with high spermatozoa concentration was diluted with seminal plasma to obtain concentrations ranging between 6 and 24 × 10⁹ mL⁻¹ with steps of 2 × 10⁹ mL⁻¹. Diluted milts were cryopreserved in 0.25-mL straws with extender (0.3 M glucose) containing 10% methanol and 10 % (vol/vol) supplement of hen egg yolk. The dilution ratio was 1:3 (milt:cryomedium). Cryopreservation efficacies were assessed according to evaluation of motility of frozen/thawed spermatozoa and quantification of fertilizing ability. Percentage of motility of frozen/thawed spermatozoa was influenced by spermatozoa concentration in the cryomedium (P < 0.05). The highest motility was observed in samples with 3.0 to 4.0 × 10⁹ spermatozoa per mL of cryomedium, which corresponds to 12 to 16 × 10⁹ spermatozoa per mL in fresh milt. Higher sperm concentrations and lower sperm concentrations in cryomedium reduced the effectiveness of cryopreservation when compared with the optimum. Cryopreservation success measured according to fertilization rate was in agreement with results for motility of frozen/thawed spermatozoa, but the optimum could not be determined with statistical precision because of differences in fertilization rate among individual donor males. However, a significant positive correlation was found between postthaw motility and fertilization rate and between cryopreserved spermatozoa velocity and fertilization rate (P < 0.05). In sea trout, cryopreservation efficiency is influenced by spermatozoa concentration in cryomedium. Individual adjustment of the dilution ratio, based on initial spermatozoa density, is recommended in the freezing protocol. Maximum cryoresistance of the cell was obtained when spermatozoa concentration in cryomedium ranged from 3.0 to 4.0 × 10⁹ mL⁻¹.     

Effect of osmotic immobilization on refrigerated storage and cryopreservation of sperm from a viviparous fish, the green swordtail Xiphophorus helleri

In this study, refrigerated storage and cryopreservation of sperm from the green swordtail Xiphophorus helleri were investigated. Previous cryopreservation research in this species utilized motile sperm because unlike in most fish species, Xiphophorus sperm can remain continuously motile after collection for a week with refrigerated storage. However, this species reproduces by internal fertilization, and given the significant requirements for motility within the female reproductive tract and potential limitations on sperm energetic capacities, immobilization of sperm prior to insemination could be used to improve fertilization success. Thus, the goal in this study was to use osmotic pressure to inhibit the motility of sperm after collection from X. helleri, and to test the effect of immobilization on refrigerated storage and cryopreservation. The objectives were to: (1) estimate the motility of sperm at different osmotic pressures, and determine an osmotic pressure suitable for immobilization; (2) cryopreserve the immobilized sperm, and estimate the motility after thawing with or without dilution, and (3) compare motility of non-immobilized and immobilized sperm after thawing, centrifugation, and washing to remove cryoprotectant. Motility was determined when sperm were suspended in 11 different osmotic pressures (24-500 mOsmol/kg) of Hanks' balanced salt solution (HBSS). Motility was observed between 116 and 425 mOsmol/kg. Sperm were not motile when the osmolality was lower than 116 or higher than 425 mOsmol/kg. Motility of the immobilized (non-motile) sperm could be activated by changing the osmotic pressure to 291-316 mOsmol/kg, and motility of immobilized sperm from hypertonic HBSS (425 mOsmol/kg) was significantly higher than that from hypotonic HBSS (145 mOsmol/kg) after 48 h of storage. At an osmolality of 500 mOsmol/kg, HBSS was used as extender to maintain immobilized sperm during cryopreservation with glycerol as the cryoprotectant. High motility (approximately 55%) was obtained in sperm after thawing when cryopreserved with 10-15% glycerol, and dilution of thawed sperm in fresh HBSS (1:4; V:V) was found to decrease the motility significantly. No difference was found in the motility of thawed sperm cryopreserved with 14% glycerol and extended in 310 and 500 mOsmol/kg HBSS. Washing by centrifugation prolonged the motility of thawed sperm from 24 to 72 h in HBSS at 310 and 500 mOsmol/kg. This study showed that sperm from X. helleri could be immobilized by use of specific osmotic pressures, and that the immobilization did not affect sperm motility after thawing. The immobilization of sperm by osmotic pressure could minimize reduction of the energetic capacities necessary for insemination, traversal, and residence within the female reproductive tract, and fertilization.     

Cellular localisation of insulin-like growth factor binding protein-2 (IGFBP-2) during development of the marine fish, Sparus aurata

The spatial localisation of insulin-like growth-factor-binding protein-2 (IGFBP-2) and its mRNA was investigated during larval and post-larval developmental stages of the gilthead seabream (Sparus aurata) by immunohistochemistry and in situ hybridisation with specific antisera and riboprobes. During larval development, immunoreactivity was found in skin, muscle, gills, pharynx, intestine, liver and olfactory epithelium. After metamorphosis, immunoreactivity was found in the oesophageal epithelium (the strongest reaction) and in red skeletal muscle, heart muscle, the thymus and the epithelium of renal tubules. In the adult, immunostaining with IGFBP-2 antibody was also found in the saccus vasculosus, ovary and testis. IGFBP-2 mRNA was detected by in situ hybridisation mainly in the intestine, skeletal musculature and ovary. These results show that IGFBP-2 protein and mRNA are expressed in a variety of seabream tissues, suggesting that IGFBP-2 regulates the actions of IGFs on these tissues during development and growth.This work was supported by grants from the University of Padua (Progetto di Ateneo, 2001) and by the US–Israel Binational Agricultural Research and Development Fund (BARD, Project IS-2769-96R)     

Protective effects of propolis on cryopreservation of common carp (Cyprinus carpio) sperm

Cryopreservation of sperm is common procedures in aquaculture, particularly used for routine in artificial insemination. However, these application cause damages and adversely affected sperm motility, viability and consequently lower hatching rates. The objective of this study is to determine whether propolis has an effect on cryopreservation and fertilization ability and to investigate the potential protective effect of propolis on spermatozoa of Cyprinus carpio. Many studies have been done in cryopreservation offish spermatozoa, but none of them contain propolis in extender composition. The extenders were prepared by using modified Kurokura Solution to which 10% Me₂SO added with different levels of propolis (0.2, 0.4, 0.6, 0.8 and 1 mg ml⁻¹) and 10% egg yolk (as a control without propolis). The pooled semen samples diluted at the ratio of 1:9 by the extenders were subjected to cryopreservation. The percentage and duration of motility and fertilization tests of cryopreserved sperm samples have been done immediately after thawing and compared with control and fresh semen. The extenders containing propolis exhibited higher percentage motility and motility duration than control group (P < 0.05). Especially the group IV (0.8 mg ml⁻¹ propolis) and the group V (1 mg ml⁻¹ propolis) showed significant positive effects on both post thaw motility and hatching ability. The propolis maintained the integrity of the spermatozoa during the cryopreservation process. Evaluating with its contents, it has been shown that propolis is an appropriate cryoprotective agent in fish semen.