Sperm handling in aquatic animals for artificial reproduction

Seasonal seminal quality variations and vitrification prospects in black flounder Paralichthys orbignyanus

Long-term preservation of gametes has been identified as a tool to improve broodstock management and increase the number of juveniles produced by artificial fertilization. Paralichthys orbignyanus is an important commercial and recreational species distributed in marine and estuarine waters from Rio de Janeiro (Brazil) to the San Matías Gulf (Argentina). This work focused on studying the seminal quality of tank-reared P. orbignyanus, demonstrating that males are fluent year-round, with the highest yields at the early reproductive season. Fresh sperm exhibited good forward swimming, and samples could be refrigerated up to 48 h while retaining their motility after activation. The optimal conditions for P. orbignyanus sperm motility activation were established as 950 mOsmol/Kg and pH values between 7 and 7.9. Additionally, a well-defined protocol for semen vitrification was developed to assess the cryotolerance of this species' sperm. We successfully produced high-quality sperm samples, using two vitrification formulations containing trehalose and both z-1000 and x-1000 polymers, that can be used in a near-future in vitro embryo production program.

40 'wild' years: the current reality and future potential of assisted reproductive technologies in wildlife species

Over the past 40 years, assisted reproductive technologies (ARTs) have grown significantly in scale and innovation, from the bovine embryo industry's shift from in vivo derived to in vitro produced embryos and the development of somatic cell-based approaches for embryo production. Domestic animal models have been instrumental in the development of ARTs for wildlife species in support of the One Plan Approach to species conservation that integrates in situ and ex situ population management strategies. While ARTs are not the sole solution to the biodiversity crisis, they can offer opportunities to maintain, and even improve, the genetic composition of the captive and wild gene pools over time. This review focuses on the application of sperm and embryo technologies (artificial insemination and multiple ovulation/in vitro produced embryo transfer, respectively) in wildlife species, highlighting impactful cases in which significant progress or innovation has transpired. One of the key messages following decades of efforts in this field is the importance of collaboration between researchers and practitioners from zoological, academic, governmental, and private sectors.

Sperm handling and management in the teleost model fish Japanese medaka (Oryzias latipes)

Japanese medaka (Oryzias latipes) has been used as a model organism in different research fields, including reproductive physiology. Sperm motility is the most important marker for male fertility in fish and, thus, reproduction success. However, because of small volume of ejaculate and short motility duration, it is still challenging to manage the sperm collection and analysis in small model fish. In the present study, we aimed to investigate sperm motility and to optimize sperm collection, short-term sperm storage, and cryopreservation in Japanese medaka (Oryzias latipes). Using two different approaches for sperm collection: testes dissection and abdominal massage, different housing conditions and activating the sperm with different activation solutions, we investigated immediate sperm motility. In the second part of this study, we used different osmolalities of immobilization solution, Hank's Balanced Salt Solution (HBSS) for sperm storage at 0, 2 and 3 h after sperm collection. Finally, the sperm were cryopreserved using methanol as cryoprotectant and HBSS as extender at two different osmolalities, and post-thaw sperm motility was investigated. The highest post-activating sperm motility was achieved in the groups activated by the extender at 300 mOsm/kg. The quality of sperm remained unaffected by co-housing with females or with males only. Furthermore, Hanks' Balanced Salt Solution (HBSS) with an osmolality of 600 mOsm/kg demonstrated its efficacy as a suitable extender for sperm storage, preserving motility and progressivity for 3 h. The highest post-thaw motility was around 35%. There were no significant differences between post-thaw motility in different groups. We also found that post-thaw incubation on ice can maintain the motility of the sperm for up to one hour after thawing.

Change in the swimming pattern of Salmo salar spermatozoa caused by the high temperature of the sperm motility activation medium

Fish are ectotherms and many have an external reproductive mode. An environmental factor which triggers fish reproductive activity in fish is water temperature. However, climate change is causing increasingly frequent events in which the water temperature varies rapidly; as a result, both in hatchery and in natural conditions, fish sperm are exposed to varying environmental temperatures during their journey toward the egg. This study was based on two experiments: The first experiment was designed to determine how storage at 4 °C for four days affected the sperm functions of Atlantic salmon (Salmo salar) sperm collected by either abdominal massage (stripping/Pure) or testicular dissection (testicular macerate/Macerated). Further, computer-assisted semen analysis (CASA) was used to compare sperm velocity parameters (VCL, VSL, and VAP) and progressivity (STR, LIN, and WOB) after motility activation at different temperatures (8 and 16 °C) of sperm collected by both methods (Pure vs Macerated). The results show that spermatozoa from Macerated samples maintained a higher sperm function when stored at 4 °C for 4 days compared to Pure sperm samples. In the second experiment, CASA determined that all parameters for sperm velocity (VCL, VSL, and VAP) and progressivity (STR (50%/55%), LIN (25%-32%), and WOB (51%-57%) were affected by activation temperature (P < 0.05) and that the motility patterns after activation at 16 °C (P < 0.05), specifically the LIN or STR swimming trajectories of the sperm differed between the two groups. In conclusion, the sperm quality of testicular Macerate was superior to that of Pure sperm abdominal mass, based on the higher quality of various sperm functions during short-term storage. Moreover, there was a significant effect of the temperature of the activation medium on sperm speed and progressivity (motility pattern) in the collected samples of testicular macerate. The sensitivity of Salmo salar spermatozoa to elevated temperature varies markedly between collection methods (Pure and Macerated).

Ovarian lavage / artificial insemination method as an alternative approach for controlled reproduction of the northern pike (Esox lucius)

This study aimed to compare the effectiveness of the ovarian lavage / artificial insemination method with the traditional hormonal administration and fertilization methods over the artificial reproduction of the northern pike (Esox lucius). For this purpose, groups of five females were treated as follows: intraperitoneal injection of saline (C1); ovarian lavage with saline (C2); intraperitoneal injection of carp pituitary extract (CPE, T1); ovarian lavage with CPE (T2); intraperitoneal injection of CPE and ovarian lavage with semen after 72 h (T3); ovarian lavage with CPE and ovarian lavage with semen after 72 h (T4). According to the results, no fish ovulated in the control groups (C1 and C2). There were no significant differences (n.s.) among experimental treatments (P > 0.05, n.s.) in the reproductive parameters, such as latency time, ovulation rate, stripped egg amount, and pseudo-gonadosomatic index. The lowest fertilization rate (54.8%) was observed in the T4 treatment and significantly differed from the T1 and T2 treatments (P < 0.05). Moreover, the highest survival at swim-up stage was measured in the T4 treatment with a significant difference compared to the T1 group (P < 0.05). The survival at the eyed-egg stage, hatching rate, and malformations were similar (P > 0.05, n.s.) in all applied strategies. The results demonstrated that the ovarian lavage / artificial insemination method could be applied to control northern pike reproduction, like the traditional fertilization method. Consequently, this novel technique can be suggested as an alternative strategy to facilitate the hatchery operations in the controlled reproduction of this species.

Catalase and Uric Acid Prevent Morphological Damage to the Sperm Flagella of Colossoma macropomum During 96 Hours at Low Storage Temperatures

Oxidative stress is one of the main causes of loss of sperm function during chilled storage. The aim of the current study was to evaluate the effects of a fructose-based extender, which was supplemented with catalase or uric acid, on the motility, viability, morphological integrity, and lipid peroxidation (LPO) of Colossoma macropomum spermatozoa. Sperm was diluted in extenders containing catalase (0; 0.1; 0.8; and 1.5 kU/L) or uric acid (0; 0.25; 0.5; and 1.0 mmol/L) and then stored at 4.3 ± 0.6°C for 96 hours. The chilling storage time had more significant and pronounced effects on practically all the measured sperm quality parameters than the different concentrations of both antioxidants added to the extenders. This was true for sperm motility, motility duration, sperm viability, and the percentage of normal spermatozoa. In fact, for all these parameters, values were higher in the extenders supplemented with catalase or uric acid, than those not supplemented with these antioxidants, especially after 96 hours. The LPO process showed an antioxidant-dependent response. In catalase-supplemented extenders thiobarbituric acid reactive substance (TBARS) levels increased gradually and significantly with time, but remained stable during the 96 hours of chilled storage in all samples in which uric acid was added. Despite this, TBARS levels were lower in the extenders supplemented with both catalase and uric acid than in those not having these antioxidants. Inverse correlations were found between sperm motility and the damage in sperm flagella. Our findings suggest that the supplementation of an extender with catalase or uric acid is beneficial and protects fish sperm membranes from damage caused by oxidative stress during low-temperature storage. The extenders containing 0.1 kU/L of catalase and 0.25 mmol/L of uric acid provided effective antioxidant protection for the spermatozoa of this important Amazonian fish.

Successful cryopreservation in biodegradable containers of sperm from aquaculture Mediterranean fishes

We aimed to evaluate the efficiency of hard-gelatin and hard-hydroxypropyl methylcellulose (HPMC) capsules as biodegradable alternative containers to plastic straws in European eel (Anguilla anguilla), gilthead seabream (Sparus aurata) and European sea bass (Dicentrarchus labrax) sperm cryopreservation. Sperm samples from each European eel (n = 12) were diluted 1:8:1 (sperm: extender P1+5 % egg yolk: methanol). Gilthead seabream (n = 12) samples were individually diluted in a cryoprotectant solution of 5 % Me2SO + NaCl 1 % plus BSA (10 mg mL-1) at a ratio of 1:6 (sperm: cryoprotectant solution). European sea bass (n = 10) sperm from each male was diluted in non-activating medium (NAM) at a ratio of 1:5.7 (sperm: NAM), and 5 % of Me2SO was added. The diluted European eel and sea bass sperm aliquots (0.5 mL) were individually filled in plastic straws (0.5 mL), hard-gelatin, and HPMC capsules (0.68 mL). Gilthead seabream diluted sperm (0.25 mL) were filled in plastic straws (0.25 mL) and identical capsules described. All samples were frozen in liquid nitrogen vapor and stored in a liquid nitrogen tank. Sperm kinetic parameters were evaluated by CASA-Mot software. Sperm membrane integrity was performed using a Live and Dead KIT and an epifluorescence microscope. To quantify DNA damage, the alkaline comet assay was performed and TailDNA (TD-%) and Olive Tail Moment (OTM) were evaluated by CaspLab software. Sperm cryopreservation of the three Mediterranean species in straws, gelatin, or HPMC capsules reduced the kinetic parameters and cell membrane integrity. Generally, the post-thawing samples cryopreserved in straws and capsules did not differ for the kinetic parameters and cell membrane integrity, except for European sea bass sperm, where the samples stored in gelatin capsules showed higher velocities (VCL - 100; VSL - 76; VAP - 90 μm s-1) than the sperm stored in HPMC capsules (VCL - 87; VSL - 59; VAP - 73 μm s-1). The cryopreservation process did not damage the sperm DNA of European eel and European sea bass, regardless of the containers used. On the other hand, gilthead seabream sperm cryopreserved in gelatin (TD - 9.8 %; OTM - 9.7) and HPMC (TD - 11.1 %; OTM - 11.2) capsules showed higher DNA damage than fresh samples (TD - 3.6 %; OTM - 2.7) and the sperm stored in straws (TD - 4.4 %; OTM - 5.2). The hard-gelatin and HPMC biodegradable capsules can be used as an alternative to straws for European eel, gilthead seabream, and European sea bass sperm cryopreservation.

Establishment of a Practical Sperm Cryopreservation Pathway for the Axolotl (Ambystoma mexicanum): A Community-Level Approach to Germplasm Repository Development

The axolotl (Ambystoma mexicanum) draws great attention around the world for its importance as a biomedical research model, but housing and maintaining live animals is increasingly expensive and risky as new transgenic lines are developed. The goal of this work was to develop an initial practical pathway for sperm cryopreservation to support germplasm repository development. The present study assembled a pathway through the investigation of axolotl sperm collection by stripping, refrigerated storage in various osmotic pressures, cryopreservation in various cryoprotectants, and in vitro fertilization using thawed sperm. By the stripping of males, 25-800 µL of sperm fluid was collected at concentrations of 1.6 × 106 to 8.9 × 107 sperm/mL. Sperm remained motile for 5 d in Hanks' Balanced Salt Solution (HBSS) at osmolalities of 100-600 mOsm/kg. Sperm cryopreserved in 0.25 mL French straws at 20 °C/min in a final concentration of 5% DMFA plus 200 mM trehalose and thawed at 25 °C for 15 s resulted in 52 ± 12% total post-thaw motility. In six in vitro fertilization trials, 20% of eggs tested with thawed sperm continued to develop to stage 7-8 after 24 h, and a third of those embryos (58) hatched. This work is the first report of successful production of axolotl offspring with cryopreserved sperm, providing a general framework for pathway development to establish Ambystoma germplasm repositories for future research and applications.

The investigation of post-thaw chilled storage and the applicability of large-scale cryopreservation in chub (Squalius cephalus) sperm

Chub (reophillic cyprinids) is one of the most sensitive bioindicator fish of environmental changes following anthropogenic activities. The improvement of different biotechnological procedures could help support its conservation and strengthen the natural populations. The aim of this study was to compare the effects of two different hormonal agents (carp pituitary extract and Ovopel™) on various motility parameters (pMOT-%, DAP-μm, VCL μm s-1, VSL-μm s-1, LIN-%, ALH-μm, BCF-Hz) of fresh and cryopreserved/thawed sperm (stored at 4 °C for 6 h). Additionally, we sought to develop a novel, large-scale cryopreservation method for chub sperm, assessing freezing methods (Styrofoam box and a controlled-rate freezer) and different containers (0.5, 5 mL straw and 4 mL cryotube) for sperm cryopreservation. The results of this study indicated no difference between the carp pituitary extract and Ovopel treated groups in either the fresh or frozen/thawed sperm (at 0, 3, 6, hour post thawing, P = 0.4351). In contrast, the quality of the thawed chub sperm was negatively affected after 3 h chilled storage in both hormonal treatments (P = 0.0036, P < 0.0001). When assessing the motility parameters of the sperm between the 5 mL straw and 4 mL cryotube groups cryopreserved in a Styrofoam Box, no difference was observed (P = 0.103). Additionally, sperm loaded in 4 mL cryotubes showed no difference in motility when cryopreserved with either the Styrofoam box or controlled-rate freezer methods (P = 0.109). A similar hatching rate was observed in sperm preserved using the Styrofoam box (35 ± 7 %) and controlled rate freezer (25 ± 9 %) methods (P = 0.300). In a second fertilization trial, hatching rate was similar between control (72 ± 19 %) and cryopreserved (4 mL cryotube and Styrofoam box, 61 ± 5 %) groups. (P = 0.257). Based on our findings and its standard features (less species specific, precise dose calculation), Ovopel can be a good candidate for the stimulation of spermiation in chub sperm prior to cryopreservation. Furthermore, our study presents a novel and applicable method for the large-scale cryopreservation of chub sperm.

Comparative evaluation of the effects of different activating media and temperatures on European eel (Anguilla anguilla) sperm motility assessed by computer assisted sperm analysis

The European eel is a critically endangered teleost fish with very poor success rate for captive breeding and artificial reproduction. Therefore, to support its conservation, new strategies are needed to ensure fertilization. Objective analysis of sperm motility may be critical as it potentially represents one of the most important reproductive quality parameters. Spermatozoa acquire motility once in contact with hyperosmotic solutions as saltwater, yet the exact mechanisms and the role of temperature are still to be clarified. The main aim of the study was to assess the effects of 3 activating media (artificial sea water, tank water and commercial Actifish®) at 4 and 20 °C on sperm motility, by means of computer assisted sperm analysis. Secondary aim was to test 2 different concentrations of Actifish® mimicking sea water pH/osmolality, at 4 °C. The results suggested how both temperature and activating media have effects on spermatozoa motility and kinematics, with temperature mainly acting upon interaction with the media type. The samples activated with tank water at 20 °C showed the poorest motility outcomes (mean 38.1%), while the ones activated with Actifish® diluted 1:4 and artificial sea water, at 4 °C, the highest (means 51.8 and 51.5% respectively). Additionally, diluting Actifish® to reach same pH and osmolality of seawater led to worse motility outcomes, suggesting that composition may be the critical factor for activation rather than osmolality itself.

Optimization of a non-activating medium for short-term chilled storage of barramundi (Lates calcarifer) testicular spermatozoa

Reliable short-term chilled sperm storage is a critical prerequisite to using advanced reproductive techniques for captive breeding of barramundi (Asian sea bass; Lates calcarifer). Marine Ringer's solution (MRS) is a common non-activating medium (NAM) and has previously been used to store sperm from wild-caught barramundi. However, MRS-stored spermatozoa from captive-bred barramundi were observed to lyse within 30 min incubation. Therefore, this study aimed to optimize the composition of NAM for short-term chilled storage by characterizing and mimicking the biochemical profile of seminal and blood plasma of captive-bred barramundi. To further understand the effect of each component, osmolality was first examined to determine its effect on sperm viability. Thereafter, the effects of NaHCO3, pH, and Na+ and K+ concentrations on sperm motility were investigated. Optimization of the NAM formula was achieved through iterative adaptions. The increase in NAM osmolality from 260 to 400 mOsm/kg led to a significant improvement in sperm viability. Moreover, using HEPES instead of NaHCO3 as buffering agent significantly enhanced sperm motility and velocity. As a result, sperm samples diluted with optimized NAM (185 mM NaCl, 5.1 mM KCl, 1.6 mM CaCl2·2H2O, 1.1 mM MgSO4·7H2O, 10.0 mM HEPES, 5.6 mM D+ glucose, 400 mOsm/kg, pH 7.4) and stored at 4 °C showed no significant loss in total motility for up to 48 h and retained progressive motility for up to 72 h. The optimized NAM developed in this study significantly extended the functional lifespan of spermatozoa during chilled storage, permitting the ongoing development of advanced reproductive technologies for barramundi.

The Increasing Role of Short-Term Sperm Storage and Cryopreservation in Conserving Threatened Amphibian Species

Multidisciplinary approaches to conserve threatened species are required to curb biodiversity loss. Globally, amphibians are facing the most severe declines of any vertebrate class. In response, conservation breeding programs have been established in a growing number of amphibian species as a safeguard against further extinction. One of the main challenges to the long-term success of conservation breeding programs is the maintenance of genetic diversity, which, if lost, poses threats to the viability and adaptive potential of at-risk populations. Integrating reproductive technologies into conservation breeding programs can greatly assist genetic management and facilitate genetic exchange between captive and wild populations, as well as reinvigorate genetic diversity from expired genotypes. The generation of offspring produced via assisted fertilisation using frozen-thawed sperm has been achieved in a small but growing number of amphibian species and is poised to be a valuable tool for the genetic management of many more threatened species globally. This review discusses the role of sperm storage in amphibian conservation, presents the state of current technologies for the short-term cold storage and cryopreservation of amphibian sperm, and discusses the generation of cryo-derived offspring.

Assessment of male reproductive traits in endangered leuciscids from the Iberian Peninsula: first attempts to store gametes both at short- and long-term

During the spring of 2022, several endangered leuciscid species (Anaecypris hispanica, Squalius aradensis, Anachondrostoma Occidentale, and Iberochondrostoma lusitanicum) were sampled both at the Vasco da Gama aquarium facilities and in some rivers of the Algarve region, Portugal. Sperm samples were extracted by gentle abdominal pressure and sperm motion parameters were assessed for the first time in four species, using a computerized analysis system. The results obtained showed that spermatozoa kinetic patterns were similar for all 4 species, with high motility and velocity values after the sperm activation time and with a marked decrease after 20. On the other hand, sperm longevity was highly variable between species, with short longevities (around 40 s) for A. hispanica and S. aradensis, and longer longevities (100-120 s) for A. occidentale and I. lusitanicum, which could indicate a latitudinal pattern in terms of sperm longevity. At the same time, morphometric analysis was carried out for the four target species, revealing that spermatozoa showed similar sizes and shapes to other external fertilizers belonging to Leuscididae, with small spherical heads, uniflagellate, and without acrosomes. In addition, a short-term gamete storage trail was performed by diluting sperm in 1:9 (sperm:extender) and storing them at 4ºC. Although the results obtained were uneven among the species studied, the dilution and extender used generated motilities above 40% up to day 4 of storage in S. aradensis and I. lusitanicum, and up to days 1-2 in A. hispanica and A. occidentale, respectively. Finally, gamete cryopreservation trials were also carried out on these threatened species. Although cryopreserved samples showed significantly lower motility than fresh samples, some protocols generate acceptable percentages of viability, DNA integrity, and sperm motility in some species such as I. lusitanicum and A. occidentale. The data revealed that the protocol based on 10% DMSO plus 7.5% egg yolk generated the best results.This study is the first to assess the reproductive traits of wild and captive populations of endangered leuciscids endemic from the Iberian Peninsula, describing the spermatozoa kinetics and developing protocols for managing male gametes both in short- and long-term storage. Outcomes will provide new and useful tools to complement the management and conservation of ex situ breeding programs that are being developed for these four endangered species.

The effectiveness of Ovaprim, Ovopel, and their combinations in artificial reproduction of common rudd Scardinius erythrophthalmus under controlled conditions

In this study, a practical protocol for artificial reproduction was developed for the rudd, Scardinius erythrophthalmus, to help to produce this fish for aquaculture industries and also for restocking programs. For this purpose, the efficiency of different hormonal agents and their combinations for spawning induction of female breeders of rudd was evaluated. Ovulations were stimulated using different treatments as: two injections of Ovaprim (Ova), two injections of Ovopel (Ovo), a priming dose of Ovopel with a resolving dose of Ovaprim (Comb1), a priming dose of Ovaprim with a resolving dose of Ovopel (Comb2), and two injections of sterile 0.9% NaCl solution as a control group. During the study, ovulation success, egg developmental competence as well as the performance of the freshly hatched larvae were recorded. There was no ovulation in females from the control group. In hormone-treated groups, 84-100% of fish ovulated, but no differences were observed in ovulation success (P > 0.05). The shortest latency period in treated fish was recorded in the Ovo group (431.6 degree-hour, P < 0.05). The best results in terms of working fecundity (number of obtained eggs per fish), relative fecundity, fertilization success, hatching rate, and embryo survival up to the eyed stage were achieved in the Ova and Comb1 groups (P < 0.05). Moreover, better survival rates up to the absorbing yolk sac stage and the lowest abnormality of larvae were observed in Ova and Comb1 groups (P < 0.05). There was no significant difference in the incubation time among different groups (P > 0.05). The obtained results indicate that two injections of Ovaprim and/or a priming dose of Ovopel with a resolving dose of Ovaprim are suitable for the artificial reproduction of rudd female breeders. Due to the proper effects and ease of use, two injections of Ovaprim could be recommended for the production of this species for restocking or aquaculture programs.

Use of cryoprotectors and antioxidants in sturgeon semen cryopreservation

In recent years, the possibility of increasing the low cryoresistance of sturgeon sperm by using antioxidants in basic cryoprotective media has been studied. The goal of this work was to review the current literature on impact of the cryoprotectors, well-known antioxidants and new multifunctional compounds on the activity indicators and fertilizing capability of sperm, as well as on biomarkers of cryostress. A special attention is given to the radical scavenging activity of studied compounds in relation to the highly reactive oxygen species, to prevent and negate oxidative stress damage of sturgeon sperm. Also, new trends for future research through the application of novel polyfunctional antioxidants to sturgeon sperm cryopreservation were indicated.

Evaluate effects of the dilution medium and holding time on various motility parameters of delta smelt semen

Sperm preservation is an efficient technique used for the recovery, conservation, and management of some endangered fish species. The present study was conducted to explore how preservation time would affect sperm and spawning performance in the endangered delta smelt (Hypomesus transpacificus). Sperm were preserved with the modified Hanks balanced salt solution at 14.7-16.9 °C. The Kruskal-Wallis test of sperm parameters using OpenCASA plugin in ImageJ software showed that sperm (n = 33♂) had significantly higher velocity and motility within the first 5 s after activation than that of other time points, while sperm had the lowest velocity and motility after 3 min post activation (P < 0.001). The findings (n = 30♂) also showed fresh sperm had higher velocity and motility than preserved sperm, while the sperm preserved for over 24 h showed a significantly low performance (P < 0.001). The nonlinear mixed effects models of fertilization results (n = 14♂ × 70♀) indicated the fresh sperm and sperm preserved for 1 h had higher fertilization rates than other preservation times (P < 0.001). The hatching rate (n = 14♂ × 70♀) also showed the fresh sperm and sperm preserved for 3 min and 1 h had higher hatching rates than other preservation times (P < 0.001). Overall, the study showed the best sperm performance in delta smelt was found within the first 5 s post activation, and the best fertilization and hatching rates were found when the sperm were fresh and preserved for 1 h. The findings of this study provide information for the first time about how long the delta smelt's sperm are motile for quality analysis, and how the preservation time can affect sperm quality, fertility, and hatching of this species for future applications.

The Importance of Developing and Standardizing Gamete, Embryo and Larvae Handling in Aquatic Animals

Artificial reproduction in aquatic animals usually involves the collection and handling of gametes both from males and females in a way that secures their quality and optimizes the fertilization event [...].

Dimethyl acetamide and dimethyl sulfoxide associated at glucose and egg yolk for cryopreservation of Pseudoplatystoma corruscans semen

Abstract This study aimed to develop a protocol for the cryopreservation of Pseudoplatystoma corruscans semen. For this, mature males were hormonally induced with a single dose of carp pituitary extract (5 mg/kg body weight). Semen was collected and evaluated. Two cryoprotectants were tested to compose the diluents: dimethyl acetamide (DMA) and dimethyl sulfoxide (Me2SO), in two concentrations (8% and 10%), + 5.0% glucose + 10% egg yolk. The semen was diluted in a 1: 4 ratio (semen: extender), packed in 0.5 mL straws and frozen in a dry shipper container in liquid nitrogen vapors. After thawing, sperm kinetics, sperm morphology and DNA integrity of cryopreserved sperm were evaluated. Pseudoplatystoma corruscans males produced semen with sperm motility > 80%. After thawing, all treatments provided semen with total sperm motility > 40%, with no significant difference (P < 0.05) between them, as well as between the other sperm kinetic parameters evaluated. The treatments with DMA provided a smaller fragmentation of the DNA of the gametes. Sperm malformations were identified in both fresh and cryopreserved semen, with a slight increase in these malformations being identified in sperm from thawed P. corruscans semen samples.

Post-thaw dilution of Rhamdia quelen sperm improves the reproductive success

The aim was to evaluate the effect of a post-thaw dilution of Rhamdia quelen sperm in 1.1% NaCl (325 mOsm kg^-1; pH 7.6; 24 °C) solution on the quality and reproductive capacity. Sperm from eight males were cryopreservation in nitrogen vapor at - 170 °C for 18 h in 0.25 mL straws in a freezing medium containing 5% fructose, 5% Powdered milk, and 10% methanol. The samples were thawed and post-thaw diluted (1:20) in NaCl solution or not (control). The higher spermatozoa velocities were observed in the post-thaw diluted samples (curvilinear (VCL) - 69 ± 11 µm s^-1; average path (VAP) - 45 ± 8 µm s^-1; straight-line (VSL) - 43 ± 8 µm s^-1) compared to the control (VCL - 47 ± 10 µm s^-1; VAP - 31 ± 6 µm s^-1; VSL - 30 ± 6 µm s^-1). Greater straightness (STR), progression (PROG), and beat cross frequency (BCF) were observed in the post-thaw diluted samples (STR - 96 ± 7%; PROG - 666 ± 128 µm; BCF - 42 ± 2 Hz) than in control (STR - 95 ± 5%; PROG - 463 ± 92 µm; BCF - 40 ± 2 Hz). The strongly curled tail was the only morphology change that differ between the post-thaw diluted (5 ± 2%) and control (2 ± 1%). Membrane integrity, mitochondrial activity, and normal larvae rate were not different between treatments. Fertilization and hatching were higher in the post-thaw diluted sperm (93 ± 3%; 82 ± 9%) when compared to control samples (65 ± 13%; 55 ± 17%). Were used oocytes from one female, limiting these results. The post-thaw dilution improved the sperm kinetics and reproductive parameters. Thus, this methodology can be included in the sperm cryopreservation protocol for R. quelen.

Seasonal changes in the milt quality of spotted scat, Scatophagus argus: Implications for artificial propagation

The current study investigated the correlation among sperm production (milt volume, spermatocrit and sperm count), sperm motility characters and biochemical composition of seminal plasma during different seasons to estimate the quality of semen in the Spotted scat (Scatophagus argus). The sperm of 120 males were collected over a period of 2 years seasonally viz., summer, pre-monsoon, monsoon and post-monsoon. During the collection period, it was observed that there were significant (p < 0.05) seasonal variations in the semen quality including sperm motility and production more in the summer season than other seasons. The osmolality of seminal plasma varied from 343.33 to 370.33 mOsm/kg. The pH of seminal plasma elevated from 7.37 to 7.63 during monsoon and summer seasons. The motility of S. argus sperms correlated with the concentration of biochemical compounds viz., Ca²⁺, Mg⁺ and Cl^- during the summer season. Based on the present observation it could be highlighted that sodium and potassium were negatively correlated (p < 0.01 and p < 0.05) effect on total protein (r = -0.826; -0.956), glucose (r = -0.819; -0.717), cholesterol (r = -0.978; -0.849), AST (r = -0.853; -0.897), ALT (r = -0.970; -0.967), calcium (r = -0.850; -0.697), magnesium (r = -0.852; -0.843) and chloride (r = -0.906; -0.926). In conclusion, many physical and biochemical compositions of S. argus semen improved during that the summer and pre-monsoon season as compared to that of monsoon and post-monsoon. Fertility tests were performed to determine the ability of spermatozoa to fertilize an egg. Highest fertilization (79.92 ± 4.60%) and hatching (80.75 ± 3.89%) rates were observed during summer, while the rates were lowest during monsoon (40.50 ± 4.52%; 53.92 ± 7.38%). This work forms a compiled data for standard semen quality, which in turn will help to select good milters for hatchery production, cryopreservation and assisted breeding programs of this fish.

Comparative Study of Semen Parameters and Hormone Profile in Small-Spotted Catshark (Scyliorhinus canicula): Aquarium-Housed vs. Wild-Captured

Simple Summary

Comprehensive knowledge of chondrichthyan reproductive biology is crucial for the development of reproductive technologies. For that reason, a male reproductive evaluation was performed on the basis of a comparison of samples collected from wild-captured and aquarium-housed small-spotted catshark (Scyliorhinus canicula). Semen quality, sperm morphometry, and reproductive hormones were assessed. The results demonstrate good in vitro semen quality in aquarium-housed sharks, although there was lower plasma testosterone.

Abstract

Several chondrichthyan species are threatened, and we must increase our knowledge of their reproductive biology in order to establish assisted reproductive protocols for ex situ or in situ endangered species. The small-spotted catshark (Scyliorhinus canicula) is one of the most abundant shark species of the Mediterranean coast and is easy to maintain in aquaria; therefore, it is considered an ideal reproductive model. This study aimed to compare S. canicula male reproductive function in aquarium-housed (n = 7) and wild-captured animals, recently dead (n = 17). Aquarium-housed animals had lower semen volume (p = 0.005) and total sperm number (p = 0.006) than wild-captured animals, but similar sperm concentrations. In terms of sperm parameters, aquarium-housed sharks showed higher total sperm motility (p = 0.004), but no differences were observed regarding sperm viability, mitochondrial membrane potential, or membrane integrity. A morphometric study pointed to a significantly longer head (p = 0.005) and acrosome (p = 0.001) in wild-captured animals. The results of the spermatozoa morphological study of S. canicula were consistent with previous results obtained in other chondrichthyan species. With regard to sex hormones, testosterone levels were significantly lower in aquarium-housed animals (p ≤ 0.001), while similar levels of 17β-estradiol and progesterone were found. In short, the present study provides evidence of good in vitro semen quality in S. canicula housed in an aquarium, underlining their excellent potential for application in reproductive technologies for this and other chondrichthyan species.

Swarming Aqua Sperm Micromotors for Active Bacterial Biofilms Removal in Confined Spaces

Microscale self-propelled robots show great promise in the biomedical field and are the focus of many researchers. These tiny devices, which move and navigate by themselves, are typically based on inorganic microstructures that are not biodegradable and potentially toxic, often using toxic fuels or elaborate external energy sources, which limits their real-world applications. One potential solution to these issues is to go back to nature. Here, the authors use high-speed Aqua Sperm micromotors obtained from North African catfish (Clarias gariepinus, B. 1822) to destroy bacterial biofilm. These Aqua Sperm micromotors use water-induced dynein ATPase catalyzed adenosine triphosphate (ATP) degradation as biocompatible fuel to trigger their fast speed and snake-like undulatory locomotion that facilitate biofilm destruction in less than one minute. This efficient biofilm destruction is due to the ultra-fast velocity as well as the head size of Aqua Sperm micromotors being similar to bacteria, which facilitates their entry to and navigation within the biofilm matrix. In addition, the authors demonstrate the real-world application of Aqua Sperm micromotors by destroying biofilms that had colonized medical and laboratory tubing. The implemented system extends the biomedical application of Aqua Sperm micromotors to include hybrid robots for fertilization or cargo tasks.

Spotted Wolffish Broodstock Management and Egg Production: Retrospective, Current Status, and Research Priorities

The first artificially fertilized spotted wolffish (Anarhichas minor) eggs hatched in Norway in the mid-1990s as this species was considered by Norwegian authorities to be a top candidate species for cold-water aquaculture in the North Atlantic regions. Previous research conducted in Norway (since 1992) and Canada (since 2000), focused on identifying key biological parameters for spotted wolffish cultivation which led, respectively, to the rapid establishment of a full commercial production line in northern Norway, while Québec (Canada) is witnessing its first privately driven initiative to establish commercial production of spotted wolffish on its territory. The control of reproduction can be viewed as a major requirement to achieve the development of performant strains using genetic selection tools and/or all-year-round production to bring about maximal productivity and synchronization among a given captive population. Although the basic reproduction aspects are more understood and controlled there are still some challenges remaining involving broodstock and upscaling of operations that limit the achievement of a standardized production at the commercial level. Quality of gametes is still considered a major constraint and it can be affected by multiple factors including nutrition, environmental conditions, handling practices, and welfare status. Internal insemination/fertilization and the protracted incubation period are challenging as well as the establishment of a health monitoring program to secure large-scale operations. The profound progress achieved in the control of reproduction, sperm handling, and cryopreservation methods for this species is presented and discussed. In this review, we also go into detail over the full range of up-to-date cultivation practices involving broodstock and identify areas that could benefit from additional research efforts (i.e., broodstock nutrition, health and welfare, scaling-up egg and larval production, genetics, and development of selective breeding programs).

A Review on Environmental Contaminants-Related Fertility Threat in Male Fishes: Effects and Possible Mechanisms of Action Learned from Wildlife and Laboratory Studies

Increasing global rates of diminished fertility in males has been suggested to be associated with exposure to environmental contaminants (ECs). The aquatic environments are the final repository of ECs. As the reproductive system is conserved in vertebrates, studies on the effects of ECs on fertility endpoints in fishes provide us with valuable information to establish biomarkers in risk assessment of ECs, and to understand the ECs-related fertility threat. The aim of the present review was to evaluate associations between ECs and fertility determinants to better understand ECs-related male fertility threat in male fishes. Wildlife studies show that the reproductive system has been affected in fishes sampled from the polluted aquatic environment. The laboratory studies show the potency of ECs including natural and synthetic hormones, alkylphenols, bisphenols, plasticizers, pesticides, pharmaceutical, alkylating, and organotin agents to affect fertility determinants, resulting in diminished fertility at environmentally relevant concentrations. Both wildlife and laboratory studies reveal that ECs adverse effects on male fertility are associated with a decrease in sperm production, damage to sperm morphology, alternations in sperm genome, and decrease in sperm motility kinetics. The efficiency of ECs to affect sperm quality and male fertility highly depends on the concentration of the contaminants and the duration of exposure. Our review highlights that the number of contaminants examined over fertility tests are much lower than the number of contaminants detected in our environment. The ECs effects on fertility are largely unknown when fishes are exposed to the contaminants at early developmental stages. The review suggests the urgent need to examine ECs effects on male fertility when a fish is exposed at different developmental stages in a single or combination protocol. The ECs effects on the sperm genome are largely unknown to understand ECs-related inheritance of reproductive disorders transmitted to the progeny. To elucidate modes of action of ECs on sperm motility, it is needed to study functional morphology of the motility apparatus and to investigate ECs-disrupted motility signaling.

Ovarian inseminated sperm impacts spawning success in zebrafish, Danio rerio (Hamilton, 1822) even in the absence of a male stimulus

Reproductive obstacles have led scientists to develop novel techniques/technologies for artificial reproduction. We aimed to investigate the possibility of propagating zebrafish females using sperm ovarian lavage with and without presence of male stimulus. This experiment consisted of several treatments: traditional spawning approaches with females and wild-type males (AB♀ × AB♂); no males present with non-manipulated females (AB♀); no males present with females inseminated with NaCl into ovarian lobes [AB♀(inj.NaCl)]; no males present with females inseminated with sperm from transgenic males into ovarian lobes [AB♀(inj.Tg♂)]; non-manipulated females kept separately from wild-type males (AB♀|AB♂); females kept separately from wild-type males and inseminated with NaCl into ovarian lobes [AB♀(inj.NaCl)|AB♂]; and females kept separately from wild-type males and inseminated with sperm from transgenic males into ovarian lobes [AB♀(inj.Tg♂)|AB♂]. There were no released eggs in both negative control treatments (AB♀ and AB♀|AB♂). Egg production increased (ranged from 0 to 28.5 eggs/female) when females were injected in the presence [AB♀ (inj.NaCl) |AB♂] or absence of male stimulus [AB♀ (inj.NaCl) and (AB♀(inj.Tg♂)]. A further increase in egg production [relative to AB♀, AB♀ (inj.NaCl), and AB♀|AB♂] was detected when females were inseminated with pooled sperm from transgenic males in the presence of male stimulus [AB♀(inj.Tg♂)|AB♂; ranged from 2.5 to 55 eggs/female] or when using traditional spawning approaches (AB♀ × AB♂; ranged from 25 to 131 eggs/female). Females inseminated with sperm produced embryos, although no differences were detected when females were inseminated with pooled sperm from transgenic males in presence (11.8 ± 16.3%) or absence (average = 12.6 ± 9.2%) of male stimulus. Traditional spawning approaches produced the most eggs (81.2 ± 42.3 per female) and highest fertilization rate (81.3 ± 10.4).

Protein Identification of Spermatozoa and Seminal Plasma in Bottlenose Dolphin (Tursiops truncatus)

Proteins play an important role in many reproductive functions such as sperm maturation, sperm transit in the female genital tract or sperm-oocyte interaction. However, in general, little information concerning reproductive features is available in the case of aquatic animals. The present study aims to characterize the proteome of both spermatozoa and seminal plasma of bottlenose dolphins (Tursiops truncatus) as a model organism for cetaceans. Ejaculate samples were obtained from two trained dolphins housed in an aquarium. Spermatozoa and seminal plasma were analyzed by means of proteomic analyses using an LC-MS/MS, and a list with the gene symbols corresponding to each protein was submitted to the DAVID database. Of the 419 proteins identified in spermatozoa and 303 in seminal plasma, 111 proteins were shared by both. Furthermore, 70 proteins were identified as involved in reproductive processes, 39 in spermatozoa, and 31 in seminal plasma. The five most abundant proteins were also identified in these samples: AKAP3, ODF2, TUBB, GSTM3, ROPN1 for spermatozoa and CST11, LTF, ALB, HSP90B1, PIGR for seminal plasma. In conclusion, this study provides the first characterization of the proteome in cetacean sperm and seminal plasma, opening the way to future research into new biomarkers, the analysis of conservation capacity or possible additional applications in the field of assisted reproductive technologies.

Is it possible to store spotted wolffish (Anarhichas minor) sperm by refrigeration?

Spotted wolffish Anarhichas minor reproduction in captivity is dependent on in vitro fertilization. However, it is often challenging to acquire sufficient fresh sperm to fertilize the eggs that are obtained. In this study, we evaluate the possibility to store spotted wolffish sperm by refrigeration. Spotted wolffish sperm has the particularity that is already motile on stripping, and currently it is not possible to immobilize and reactivate. Thus, sperm refrigeration protocols should focus in extending this motility period that usually lasts up to 2 days. In a first experiment, we evaluated the possibility that the motility period of the sperm was limited by contamination with urine. The urea concentration in the sperm obtained both by stripping (17.10 ± 1.98 mg/dL) and directly from the testis (12.59 ± 2.37 mg/dL) was similar (p > 0.05), which indicate that the sperm collection method used avoid contamination with urine. Afterwards, we tested the possibility that the sperm motility period was limited by energy stores. The ATP concentration (initial value 5.65 ± 0.86 nmol/109 cells) remained stable (p = 0.099) during 30 h after sperm collection, and similar values (p = 0.329) were recorded at end of sperm storage in both diluted (3.88 ± 1.35 nmol/109 cells) and undiluted samples (4.76 ± 1.08 nmol/109). This indicates that the low intracellular ATP consumption, derived from the slow sperm motility, can probably be compensated rapidly enough by mitochondrial synthesis of ATP in the spotted wolffish sperm. In both experiments, diluted sperm kept higher percentage of motile cells during the storage time.

Optimization of Sperm Management and Fertilization in Zebrafish (Danio rerio (Hamilton))

The aim of the present study was to investigate the spontaneous motility of spermatozoa and to optimize sperm collection, short-term sperm storage, and fertilization in zebrafish Danio rerio. The movement of spermatozoon in water was propagated along the flagellum at 16 s after sperm activation then damped from the end of the flagellum for 35 s and fully disappeared at 61 s after activation. For artificial fertilization, milt must be added to an immobilizing solution, which stops the movement of sperm and keeps the sperm motionless until fertilization. E400 and Kurokura as isotonic solutions were shown to be suitable extenders to store sperm for fertilization for 6 h. E400 stored sperm for 12 h at 0-2 °C. Sperm motility decreased only to 36% at 12 h post stripping for the E400 extender and to 19% for the Kurokura extender. To achieve an optimal level of fertilization and swim-up larvae rates, a test tube with a well-defined amount of 6,000,000 spermatozoa in E400 extender per 100 eggs and 100 µL of activation solution has proven to be more successful than using a Petri dish. The highest fertilization and swim-up larvae rates reached 80% and 40-60%, respectively, with milt stored for 1.5 h in the E400 extender at 0-2 °C.

A generalized approach for sperm cryopreservation in the genus Pomoxis: Sperm cryopreservation and fertilization efficiency of black-stripe black crappie, Pomoxis nigromaculatus

Approaches for white crappie, Pomoxis annularis sperm cryopreservation have led to interest in applying similar methods to black-stripe black crappie, Pomoxis nigromaculatus. Their rarity in wild populations makes them a preferred phenotype for hatchery use. Sperm cryopreservation procedures were compared between black-stripe black crappie and white crappie for sperm motility and egg fertilization rate. There was no difference in black-stripe black crappie sperm motility after thawing between 5% dimethyl sulfoxide (DMSO, 45% motility) and 10% methanol (50% motility). However, fertilization rates were higher (p < .001) for sperm cryoprotected with 5% DMSO (38 ± 8%) than 10% methanol (22 ± 7%). Hatchery use requires sperm-to-egg ratios and fertilizing potential of single doses (i.e., 0.5 ml straw). Using black-stripe black crappie sperm (2.5 × 108 sperm/ml; 5% DMSO), the highest fertilization (27%) was found using single straws with 785 eggs (0.25 ml); total sperm:egg ratio: 159,000:1; motile sperm:egg ratio: 71,700:1. Therefore, sperm of two Pomoxis species could be cryopreserved using 350 mOsmol/kg Hanks' balanced salt solution as an extender, 5% DMSO as a cryoprotectant, cooling at 40°C/min, and thawing for 8 s at 40°C to maintain sperm motility and fertility. Basic protocols can be generalized within a genus if variables such as sperm concentration, process timing, and sample volumes are controlled.

Low sperm to egg ratio required for successful in vitro fertilization in a pair-spawning teleost, Senegalese sole (Solea senegalensis)

Cultured Senegalese sole (Solea senegalensis) breeders fail to spawn fertilized eggs. The implantation of large-scale in vitro fertilization protocols, to solve this problem, has been frustrated by low production of poor quality sperm. Cultured females were induced to ovulate with a 5 µg kg^-1 single injection of gonadotropin-releasing hormone agonist (GnRHa) and viable eggs (82.6 ± 9.2% fertilization) were stripped 41:57 ± 1:46 h after the injection. Sperm was collected from cultured males, diluted in modified Leibovitz and used fresh to fertilize the eggs. Males were not treated with hormones. A nonlinear regression, an exponential rise to a maximum (R = 0.93, p < 0.0001) described the number of motile spermatozoa required to fertilize a viable egg and 1617 motile spermatozoa were sufficient to fertilize 99 ± 12% (±95% CI) of viable eggs. Similar, spermatozoa egg^-1 ratios of 592 ± 611 motile spermatozoa egg^-1 were used in large-scale in vitro fertilizations (190 512 ± 38 471 eggs). The sperm from a single male (145 ± 50 µl or 8.0 ± 6.8 × 10⁸ spermatozoa) was used to fertilize the eggs. The mean hatching rate was 70 ± 14% to provide 131 540 ± 34 448 larvae per fertilization. The viability of unfertilized eggs stored at room temperature decreased gradually, and the sooner eggs were fertilized after stripping, the higher the viability of the eggs. The collection of sperm directly into a syringe containing modified Leibovitz significantly increased the percentage of motile spermatozoa (33.4 ± 12.2%) compared with other collection methods. The spz egg^-1 ratios for Senegalese sole were at the lower end of ratios required for fish. Senegalese sole have a pair-spawning reproductive behaviour characterized by gamete fertilization in close proximity with no sperm competition. The provision of a large-scale in vitro fertilization protocol (200 µl of sperm per 100 ml of eggs) will enable the industry to operate sustainably and implement breeding programmes to improve production.

Inseminating dose for the artificial fertilization of Brycon amazonicus (Teleostei: Characidae)

Knowledge of the sperm-oocyte ratio in fish fertilization serves as the basis for studies on artificial reproduction and gamete manipulation. The aim of this study was to determine the minimum insemination dose for Brycon amazonicus oocyte fertilization. Female and male gametes were used and tested with the following doses of spermatozoa oocyte-1 ml-1: 10,000, 20,000, 40,000, 60,000 and 80,000 (in triplicate). Fertilization rates were calculated and estimated from the regression equation by applying the segmented regression model 'Linear Response Plateau' to determine the appropriate proportion of gametes. Based on the equation Ŷ = 14.3415 + 0.0007836X, the fertilization rate increased up to 63.34% as it reached a plateau with a proportion of 62,524 spermatozoa oocyte-1 ml-1, which is the minimum insemination dose recommended for artificial insemination of the species.

Effect of exogenous lipids on cryotolerance of Atlantic salmon (Salmo salar) spermatozoa

The development of semen cryopreservation strategies is necessary to improve the semen storage technologies of species of great commercial interest for aquaculture. Recent studies demonstrate that lipids play an important role in the fertility and cryotolerance of fish gametes. This study investigated the effect of exogenous lipids in the freezing medium on the post-thaw functional parameters of Salmo salar spermatozoa. Semen samples (n = 12) were incubated in standard extender supplemented with different concentrations of oleic acid (OA, C18:1n9), linoleic acid (LA, C18:2n6), arachidonic acid (ARA, C20:4n6) and cholesterol-loaded cyclodextrin (CLC). Post-thaw motility, membrane integrity, mitochondrial membrane potential (ΔΨm), superoxide anion (O₂^•-) and fertility rates were analyzed. The results revealed that the semen incubated with 0.003 mmol/L OA increased the motility (~7%) and ΔΨm (~2%) (P < 0.05), but membrane integrity and fertility were not increased. The addition of 0.003 mmol/L LA increased the motility (~4%) and all LA extenders increased the ΔΨm (P < 0.05); however, LA increased the O₂^•- levels and decreased the membrane integrity and fertility (P < 0.05). Semen incubated with ARA improved sperm motility (~5%), membrane integrity (~10.5%) and fertility rates (~11%) (P < 0.05). The maximum improvement in post-thaw sperm functionality was observed by adding 0.003 mmol/L ARA. In contrast, sperm quality parameters and fertility were decreased by the CLC addition (P < 0.05). This study showed that ARA could be considered as an additive for semen cryopreservation and could be relevant in the reproductive process and reproductive management of Salmo salar.

Effects of gametes post-activation, egg storage and sperm-egg ratio on in vitro fertilization outcomes in the brown-marbled grouper (Epinephelus fuscoguttatus)

Due to some biological characteristics of the brown-marbled grouper, there are challenges in aquaculture enterprises focused on production of this fish. With the aim of facilitating captive breeding in brown-marbled grouper, effects on gamete post-activation, post-stripping egg storage and sperm to egg ratio on fertilization success were investigated. Results indicated eggs were fertile for 4 min after placement in seawater, thereafter, there was a reduction in fertilization. Initial curvilinear velocity (VCL) and total motility of fresh sperm was 129.3 ± 3.7 μm/s and 92.9 ± 2.4 %, both of which decreased as time elapsed post-activation, however, there was no significant difference in fertilization until 6 min post-activation of sperm. Compared with fertilization and hatching rates in eggs used immediately after collection (95.0 ± 2.8 % and 90.1 ± 4.2 %), in vitro storage of eggs had no detectable effect on fertilized egg and hatching rates until 60 min post-stripping (92.0 ± 2.8 % and 89.9 ± 2.7 %), indicating that immediate use of brown-marbled grouper eggs for fertilization is not necessary in aquaculture hatcheries. With regard to optimizing the sperm to egg ratio, there was acceptable fertilization with ratios ranging from 10³ to 10⁷, whereas there was a marked decrease in fertilization rate when there were lesser sperm concentrations. When the combined results from this study are considered, there could be improvements of artificial fertilization efficiency in the brown-marbled grouper with utilization of these findings in aquaculture enterprises focused on production of this fish.

Short-term storage sperm of coho salmon (Oncorhynchus kisutch) at 4 °C: Effect of sperm: Extender dilution ratios and antioxidant butyl-hydroxytoluene (BHT) on sperm function

Short-term storage of semen is a necessary key procedure in fish; it allows maximizing the use of gametes. Nevertheless, sperm quality decreases during storage has been associated with oxidative stress damage due to an increase in reactive oxygen species (ROS) during storage. This study was designed to optimize a short-term storage protocol for Coho salmon (Oncorhynchus kisutch) spermatozoa, evaluating the effect of extender dilution and the addition of butyl-hydroxytoluene (BHT) antioxidant on sperm function parameters. In the first experiment, fresh semen was diluted in Storfish®: extender dilution (1:2 and 1:3) and a control sample undiluted and stored at 4 °C for 7-days. In both experiments motility (MO), viability and integrity of plasma membrane, mitochondrial membrane potential (MMP) and superoxide anion level (O₂^-) were evaluated at 0, 3 and 7 days. Result shows that, 1:3 dilution maintained a higher sperm function for a longer period time. In the second experiment, spermatozoa were suspended in Storfish® (1:3) supplemented with two different concentrations of BHT (1.0 mM and 2.0 mM) and a control sample without antioxidant and stored at 4 °C for 7 days. The results demonstrated that, antioxidant-supplemented samples greater MO than control samples (P < 0.05). The viability remained >75% during storage in all groups. MMP was higher in 2.0 mM BHT compared to 1.0 mM and control (P < 0.05), in addition, this concentration reduced O₂^- level (P < 0.05). In conclusion, sperm: extender dilution 1:3 and adding of 2.0 mM BHT in sperm storage extender may enhance protection sperm function in Oncorhynchus kisutch against effects harmful of the oxidative stress during the in vitro storage.

Step by step optimization of a sperm cryopreservation protocol for spotted wolffish (Anarhichas minor Olafsen, 1772)

Spotted wolffish Anarhichas minor reproduction in captivity is dependent on in vitro fertilization. However, low sperm volume with relatively low cell concentration and the lack of gametes synchronization (simultaneous availability of mature eggs and sperm) represent a challenge for the industry. Thus, the development of protocols for sperm storage are crucial. Four sequential experiments were conducted to optimize a sperm cryopreservation protocol for this species. First, three different cryoprotectants (DMSO; 1, 2-propanediol; and methanol) at different concentrations (5, 10, and 20%) were tested for their toxicity. No significant differences (p > 0.05) were detected between the control samples and cryoprotectants at concentration up to 10% DMSO, 10% propanediol, and 20% methanol in terms of motility parameters. Second, using the highest non-toxic concentrations of cryoprotectants, sperm was cryopreserved in 0.5 mL straws, at different distances from the liquid nitrogen (1.5, 2.5, 4.5, and 7.5 cm) that correspond to different freezing rates. Motility parameters after freezing/thawing decreased for all the cryoprotectants (p < 0.001), however, methanol had the lowest protective capacity while DMSO the highest. Afterwards, two different thawing rates (1 min at 5 °C; and 25 s at 10 °C) were tested using only 10% DMSO and 10% propanediol. Both for the DMSO and propanediol, there were no significant differences (p > 0.05) between the two thawing rates. The best results were obtained using 10% DMSO. Finally, the fertilization capacity of cryopreserved sperm (10% DMSO and thawed at 5 °C for 1 min) was tested against fresh sperm using two spermatozoa:egg ratios and 4 h gametes contact time. The ratio of eggs with normal cell cleavage, abnormal cleavage or undeveloped were counted at the 2-4 cell stage. Cryopreserved sperm showed lower fertilization capacity at a concentration of 5 × 10⁴ spermatozoa:egg compared with fresh sperm (p < 0.001). At a concentration of 5 × 10⁵ spermatozoa:egg, similar fertilizations rates to the fresh sperm were obtained. The presence of the cryoprotectant DMSO during the 4 h contact time did not affect the fertilization rate or the percentage of embryos with abnormal cleavage (p > 0.05). To cryopreserve spotted wolffish sperm it is recommended to use 10% DMSO, loaded in 0.5 mL straws, freeze at a height between 4.5 (-14.05 °C/min) and 7.5 cm (-5.9 °C/min) from liquid nitrogen for 10 min and thaw for 1 min at 5 °C (177.9 °C/min). In vitro fertilization with cryopreserved sperm should be performed with a concentration of at least 5 × 10⁵ spermatozoa per egg.

Fish sperm competition in hatcheries and between wild and hatchery origin fish in nature

Males compete pre- and post-mating to fertilize the maximum number of eggs. In polyandry, sperm competition occurs when sperm from two or more males compete to fertilize eggs from a female. Here we review how sperm competition from hatchery origin fish can cause loss of genetic variability in fish populations kept in captivity and in wild populations. In fish hatchery practices, sperm competition occurs in mass spawners that release gametes in tanks, and in artificial fertilizations when pooled semen is used. In mass spawnings sperm competition is difficult to tease apart from pre-mating competition and other post-mating selective mechanisms, whereas, studies focused on the use of pooled semen in different fish species have shown a clear relationship between sperm motility parameters and precedence in fertilization. In both situations, sperm competition will result in a loss of genetic variability that accumulates over generations, but hatchery protocols can be adjusted to mitigate it. Another source of concern regarding sperm competition for hatchery produced fish is the spatial and temporal overlap in spawning with wild individuals, either via aquaculture escapees or purposeful stocking programs. This may result in sperm competition between hatchery origin and wild males and impact natural populations. Our review suggests that in order to give every adult selected as broodstock an equal opportunity to produce offspring in captivity, mass spawning and the use of pooled semen should be limited.

Sperm motility in fishes: (III) diversity of regulatory signals from membrane to the axoneme

Fish spermatozoa acquire potential for motility in the sperm duct where they are immotile. Osmolality of the seminal plasma is a key factor to maintain spermatozoa in the quiescent state in either freshwater or marine fishes. However, potassium (K⁺) ions prevent spermatozoa motility in salmonid and sturgeon fishes, while CO₂ inhibits spermatozoa motility in flatfishes. Once, spermatozoa are released at spawning, their motility is initiated in hypo-osmotic and hyper-osmotic environments in freshwater and marine fishes, respectively. Some substances produced by the testes (a progestin), or released from oocytes (peptides) induce spermatozoa hypermotility in some marine fishes including the Atlantic croaker and Pacific herrings, respectively. Duration of spermatozoa motility is short, lasting for a few seconds to few minutes in most fishes due to rapid depletion of energy required for the beating of the motility apparatus called axoneme. In the osmotic-activated spermatozoa, K⁺ and water effluxes occur in freshwater and marine fishes, respectively, which trigger spermatozoa motility signaling. In general, initiation of axonemal beating is associated with an increase in intracellular calcium (Ca²⁺) ions in spermatozoa of both freshwater and marine fishes and a post- or pre-increase in intracellular pH, while cyclic adenosine monophosphate (cAMP) remains unchanged. However, axonemal beating is cAMP-dependent in demembranated spermatozoa of salmonid and sturgeon fishes. Calcium from extracellular environment or intracellular stores supply required Ca²⁺ concentration for axonemal beating. Several axonemal proteins have been so far identified in fishes that are activated by Ca²⁺ and cAMP, directly or mediated by protein kinase C and protein kinase A, respectively. The present study reviews differences and similarities in complex regulatory signals controlling spermatozoa motility initiation in fishes, and notes physiological mechanisms that await elucidation.