Cryopreservation in fish: current status and pathways to quality assurance and quality control in repository development

Transitioning from a research protocol to a scalable applied pathway for Xenopus laevis sperm cryopreservation at a national stock center: The effect of cryoprotectants

Sperm cryopreservation is a critical tool for safeguarding and managing valuable genetic resources. Protocols for cryopreservation of Xenopus laevis sperm were available but lacking sperm quality evaluation and scalability and the outcomes were inconsistent. The goal of this study was to begin developing a center-level cryopreservation pathway for this species by integrating French straws as containers that would facilitate germplasm repository development. The objectives were to analyze the effect of: (1) three sperm concentrations (33, 50, and 100 × 106 sperm/mL) on post-thaw fertilization, (2) three final concentrations (2.5%, 5%, and 10%) of dimethyl sulfoxide, methanol, and dimethylformamide (DMFA) on sperm membrane integrity of fresh and frozen samples, (3) two concentrations (5% and 10%) of DMFA with and without 5% sucrose at four cooling rates (5, 10, 20, and 40°C/min) on sperm membrane integrity and motility, and (4) egg exposure to different concentrations of DMFA on fertilization. Few differences in sperm viability were found among fresh samples incubated in cryoprotectants, but thawed samples frozen in methanol or DMFA presented higher membrane integrity. Samples frozen in 10% DMFA at 20°C/min showed higher membrane integrity (60 ± 7%) than other DMFA concentrations and cooling rates, and the same total motility (30 ± 7%) as at 10°C/min. Higher DMFA concentrations (10%-13%) were detrimental for embryo development compared to lower concentrations (<6%). This study provided a reliable protocol for sperm cryopreservation in Xenopus laevis to yield an application pathway with potential for high throughput that can be used as a roadmap for work with other species.

Supplementing semen extenders with a combination of phosphorus and vitamin B12 Improves post-thawed cryopreserved rooster semen quality

Semen cryopreservation is an important technique for preserving the genetic material of numerous species. However, frozen semen is highly susceptible to sperm DNA damage and reduced motility, resulting in decreased fertility. The standard method for cryopreservation and several approaches have not been elucidated. This study aimed to determine the effects of supplementing rooster semen extender with a combination of phosphorus and vitamin B12 on cryopreserved semen quality. Semen was collected weekly via dorso-abdominal massage from 57 Burmese × Vietnam-crossbred Thai native roosters aged 1-3 years. In total, 139 semen samples were collected, pooled, and diluted to 200 million sperm per dose. The pooled sample was divided into six experimental groups: a control group (0.00%) diluted with modified Beltville Poultry Semen Extender (BPSE) and five treatment groups diluted with modified BPSE supplemented with phosphorus and vitamin B12 at concentrations 0.02, 0.04, 0.06, 0.08, and 0.10%, respectively. The semen samples were frozen and evaluated at 0, 15, and 30 min after thawing. Sperm kinematic parameters were determined using a computer-assisted sperm analysis system. Sperm quality was evaluated by measuring sperm viability, mitochondrial activity, acrosome integrity, and plasma membrane integrity. Statistical analyses were performed using a general linear mixed model (MIXED) in SAS. Factors in the statistical model were experimental groups, time after thawing, and interaction between experimental groups and time after thawing. Total and progressive motilities were greater in semen supplemented with 0.04% phosphorus and vitamin B12 compared with those in the control (p < 0.05). At 15 min post-thawing, VCL, VAP, and HPA in the 0.04% phosphorus and vitamin B12 supplementation group was greater than that in the control (p < 0.05). Phosphorus and vitamin B12 supplementation did not affect sperm kinematics at 0 and 30 min after thawing (p > 0.05). All the sperm parameters that were tested for the 0.04% phosphorus and vitamin B12 supplementation group in modified BPSE were the highest at all the timepoints after thawing. Thus, supplementing frozen semen extender with 0.04% phosphorus and vitamin B12 increased sperm motility, sperm kinematic parameters, and sperm quality.

The emerging role of open technologies for community-based improvement of cryopreservation and quality management for repository development in aquatic species

Genetic resources of aquatic species are of tremendous value, but worldwide these are maintained almost exclusively as live populations. This is extremely expensive and insecure, and largely results from a pervasive lack of production capability, quality management, and reproducibility in cryopreservation that are barriers in development of germplasm repositories. Community-based technology approaches are emerging that can stimulate research previously limited by a lack of affordable, customizable equipment. Open-access technologies can provide for custom design and fabrication not available through traditional manufacturing. This can assist repository development with robust sample production methods and strong quality management, and can greatly improve reproducibility and standardization. Open technologies can support establishment of new communities of users, makers, and developers that collectively strive to develop open hardware in a distributed (i.e., non-centralized) fashion that can yield aggregate throughput. This occurs through use of consumer-level tools, supplies, software, and equipment, free exchange of designs and modifications, and a shared sense of mission. For cryopreservation and repository development, we have identified 14 categories of open hardware for a processing pathway, and six categories for a quality management pathway. Open hardware offers economic incentives to develop repositories for aquatic species, something that has not occurred despite 70 years of research largely focused on protocol development rather than practical applications. Advanced development of custom scientific hardware enhancing open technologies will be facilitated by interdisciplinary collaboration across biological and engineering fields. This manuscript is a contribution to the Special Issue in memory of Dr. Duane Garner, a leader in the sperm biology.

Development of a Single-Piece Sperm Counting Chamber (SSCC) for Aquatic Species

Accurate determination of sperm concentration in aquatic species is important for assisted reproduction and cryopreservation, yet is challenging as current counting methods are costly or not suitable for many species. The goal of this work was to develop a simple (single-piece and single-layer photolithography) sperm counting chamber (SSCC) for aquatic species. Goldfish (Carassius auratus) and zebrafish (Danio rerio) sperm were used for evaluation in the device, which was created with soft lithography. Four designs with different geometries were evaluated for counting accuracy. Open-corner and open-midpoint designs were the most accurate with no significant differences (P > 0.05) for most of the target sperm concentrations (0.5-1.0 × 10⁸ cells/mL). The open-corner design was not significantly different from the Makler^® counting chamber intended for human sperm cells (P = 0.6) but was significantly different from a hemocytometer (P < 0.001) intended for other cell sizes. Material cost of device production was USD 16 per unit, including photolithography supplies, glass slide and coverslip, and polydimethylsiloxane. The cost can be reduced to USD 2 per unit with repeated wafer casts. This device could be further refined for resin 3-D printing and sharing via open-hardware approaches and modified to best suit species specific applications.

Cryopreservation of Hydractinia symbiolongicarpus Sperm to Support Community-Based Repository Development for Preservation of Genetic Resources

Hydractinia symbiolongicarpus is an emerging model organism in which cutting-edge genomic tools and resources are being developed for use in a growing number of research fields. One limitation of this model system is the lack of long-term storage for genetic resources. The goal of this study was to establish a generalizable cryopreservation approach for Hydractinia that would support future repository development for other cnidarian species. Specific objectives were to: (1) characterize basic parameters related to sperm quality; (2) develop a generalizable approach for sperm collection; (3) assess the feasibility of in vitro fertilization (IVF) with sperm after refrigerated storage; (4) assess the feasibility of IVF with sperm cryopreserved with various sperm concentrations; (5) evaluate feasibility of cryopreservation with various freezing conditions, and (6) explore the feasibility of cryopreservation by use of a 3-D printed open-hardware (CryoKit) device. Animal husbandry and sperm collection were facilitated by use of 3-D printed open hardware. Hydractinia sperm at a concentration of 2 × 107 cells/mL stored at 4 °C for 6 d were able to achieve 50% fertilization rate. It appeared that relatively higher sperm concentration (>5 × 107 cells/mL) for cryopreservation could promote fertilization. A fertilization rate of 41−69% was observed using sperm equilibrated with 5, 10, or 15% (v/v) cryoprotectant (dimethyl sulfoxide or methanol) for 20 min, cooled at a rate of 5, 10, or 20 °C/min from 4 °C to −80 °C, at a cell concentration of 108/mL, in 0.25 mL French straws. Samples cryopreserved with the CryoKit produced a fertilization rate of 72−82%. Establishing repository capabilities for the Hydractinia research community will be essential for future development, maintenance, protection, and distribution of genetic resources. More broadly, these generalizable approaches can be used as a model to develop germplasm repositories for other cnidarian species.

SIMULATION MODELING OF A HIGH-THROUGHPUT OYSTER CRYOPRESERVATION PATHWAY

The genetic resources of oysters in Louisiana and the Gulf of Mexico are threatened due to high unexplained oyster mortality. Germplasm repositories are collections of cryopreserved genetic material stored alongside associated information that are used to protect genetics resources and facilitate breeding programs in agricultural industries. Therefore, there is great need for oyster repositories. Development of repositories has been slow despite research on high-throughput cryopreservation protocols because of logistical complexities. The goal of this study was to begin to address the gap between cryopreservation research and repository development in oyster aquaculture by modeling a cryopreservation protocol to understand and improve the process. The steps of a high-throughput cryopreservation protocol were defined and mapped in a process flow diagram. A simulation model was created using time study data, and key bottlenecks in the process were identified. Finally, model variations using alternate types of devices (tools or equipment) were created to address the identified bottlenecks. The model was found to accurately simulate the cryopreservation process. Parameters such as number of straws frozen per oyster, batch size, and number of operators significantly affected how the model performed and device choices produced substantial improvements. Simulation modeling has the potential to inform how cryopreservation pathways and repository systems in aquatic species should be structured and operated. There is ample opportunity for future work such as analyzing the impacts of production scale on cryopreservation processes.

The Need for a Framework Addressing the Temporal Aspects of Fish Sperm Motility Leading to Community-Level Standardization

Motility is a widely available parameter that can be used to assess sperm quality of aquatic species. Sperm from fishes with external fertilization usually undergo a dynamic and short-lived period of motility after activation. The common practice of assigning a single value at an arbitrary peak of motility presents challenges for reproducibility, community-level standardization, and comparisons across studies. This study aimed to explore statistical approaches to standardize motility reporting, and to develop an initial framework for community-level standards. Sperm samples from 14 zebrafish (Danio rerio) with a total of 21,705 cells were analyzed by use of computer-assisted sperm analysis with data collection starting at 10 s after activation at 5-s intervals for 50 s. Four common motility variables were selected for analyses: curvilinear velocity, straight-line velocity, beat cross frequency, and amplitude of lateral head displacement. Cluster analysis was used to evaluate sperm subpopulations within and among males over time, least-square means was used to explore temporal aspects, and the first derivative of the regression equations was used to calculate the rate of change for the motility parameters. Cluster analysis proved informative, but overlapping ephemeral clusters were not valuable for providing standardization options. Analysis of temporal aspects and rate of change indicated opportunities for standardization by reporting the overall motility-time functions or reporting during stable time windows instead of peak motility or at random times. These approaches could minimize the inconsistencies caused by male-to-male variation and dynamic changes of subpopulations while providing comparable information. An overall temporal framework was identified for motility reporting along the collection-processing-cryopreservation-thawing sequence to provide a basis to support efforts of community-level standardization.

Development of an open hardware 3-D printed conveyor device for continuous cryopreservation of non-batched samples

A great challenge among communities participating in germplasm repository development is to obtain suitable cryopreservation equipment and devices. Commercial programmable freezers are costly and thus unaffordable to many users. Self-made devices have substantial variability among users, resulting in few opportunities for standardization across communities. The development of open hardware with the increasing accessibility of three-dimensional (3-D) printing offers rapid prototyping and easy fabrication of devices by users around the world at low cost. The present study explored the feasibility of developing operational prototypes of 3-D printed motorized cryopreservation devices for continuous freezing of non-batched samples. A controlled cooling conveyor device (CCCD) was designed and fabricated to cryopreserve sperm samples in straws that were loaded onto chain links suspended over liquid nitrogen held in a Styrofoam box. Cooling rates of 5 to 34 °C/min for 0.5-ml French straws were produced by adjusting the height of conveyor chains, slopes, and liquid nitrogen mass. The plunge temperature (-47 °C to -61 °C) was controlled by adjustment of conveyor speed. The cooling curves from the CCCD were comparable to a commercial programmable freezer. There were no significant differences in post-thaw motility of sperm from ornamental (Koi) common carp (Cyprinus carpio) among samples frozen with the CCCD and those frozen with a commercial programmable freezer. The post-thaw sperm motility was consistent among samples frozen in the CCCD across a 15-min time span. The CCCD prototypes in the present study proved to be feasible and functional as low-cost, customizable, portable, and yet standardizable options for freezing of individual (non-batched) samples. Additional design alternatives are proposed to facilitate further adaptation and development by diverse user communities.

Design, alpha testing, and beta testing of a 3-D printed open-hardware portable cryopreservation device for aquatic species

Efforts in development of germplasm repositories to preserve genetic resources of aquatic species are impeded globally by a lack of standardized, inexpensive, reproducible, and portable cryopreservation technologies. The present work demonstrates a 3-D printed standardizable freezing device that can be used with nitrogen vapor shipping dewars for on-site sperm cryopreservation for aquatic species and be distributed as open-source The SDPCD could hold 22 French straws (0.25-mL or 0.5-mL) and a quick-release ring design could eject straws directly into a canister inside a dewar by pressing a button after freezing. The final prototypes produced cooling rates of 1 to 64 °C/min for 0.25-mL straws, and 3 to 37 °C/min for 0.5-mL straws with material cost of US$3.5 for a single device and US$1,820-2,562 for batch production of 20 replicates. Progressing through design, prototyping, and testing was delineated to help guide development of other open-source devices within cryopreservation user communities.

An Impedimetric Sensing Probe Based on Printed Circuit Board Technology for Monitoring in Cryobiology Applications

Cryopreservation of living cells is an effective tool for protection, maintenance, and distribution of genetic resources, which involves exposure to cryogenic temperatures and requires precise control over various parameters to avoid potential cell damages. Hundreds of protocols have been reported for cryopreservation of aquatic species, but replicating them is challenging without a reliable monitoring technique during a cryopreservation process. In this work, we aim to use electrical impedance as a monitoring parameter to assist standardization of cryopreservation processes and reporting. Specifically, this paper reports an impedance sensing probe compatible with cryogenic temperatures and conventional containers in cryopreservation of aquatic species based on printed circuit board technology its characterization in cryopreservation conditions including different sperm extenders (buffer) compositions and concentrations, presence of cryoprotectant, and multiple cooling rates. The developed probe based on printed circuit board (PCB) technology shows a capability of measuring conditions during cryopreservation differentiating among samples with different buffer contents and cryoprotectants. The probe also demonstrates the capability to distinguish different cooling regimes and detect phase change phenomena. This PCB-based sensing platform provides quantitative impedance measurement data during the cryopreservation process at sample preparation, cooling, and while frozen. Technology such as this offers opportunities for improving the reproducibility of protocols generated by the aquatic species community and can be made widely available as open hardware.

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.

On-Site Capabilities of a Mobile Laboratory for Aquatic Germplasm Cryopreservation

Cryopreservation of genetic material can become an important tool for user groups in imperiled fishes, wild fisheries, aquaculture, and biomedical research. Persistent challenges within aquatic species cryopreservation are standardization and reliable collection of diverse, high quality samples. The overall goal of this study was to work with different user groups and cryopreserve sperm on-site at their facilities to evaluate the uses and challenges of a mobile laboratory with high-throughput and quality control capabilities comparable to those of a specialized centralized facility. The objectives were to demonstrate collection and cryopreservation of sperm of: 1) large-bodied freshwater Blue Catfish (Ictalurus furcatus) for aquaculture; 2) small-bodied freshwater Xiphophorus for biomedical and imperiled repository development, and 3) saltwater Red Snapper (Lutjanus campechanus) for wild fisheries research. Over the course of this project, the mobile laboratory traveled more than 4,000 km collecting germplasm from more than 650 male fishes. A total of 136 Blue Catfish were processed in 2015 and 2016 resulting in a total of 6,146 0.5-mL French straws. A total of 521 males from 11 different species in the genus Xiphophorus were processed over 4 d in 2015 resulting in a total of 488 0.25-mL French straws. And, a total of 17 Red Snapper males were processed during 2015 resulting in a total of 316 0.5-mL French straws. This is the first development of a mobile laboratory with high-throughput capability for aquatic species. User groups would no longer be limited to germplasm resources that can only be shipped as samples or transported as live animals to a central cryopreservation facility. Mobile laboratories create opportunities to collect higher quality germplasm, provide access to new species, and enable direct cooperation, including training, with a wide variety of user groups and applications.

Development of germplasm repositories to assist conservation of endangered fishes: Examples from small-bodied livebearing fishes

Germplasm repositories are a necessary tool for comprehensive conservation programs to fully preserve valuable genetic resources of imperiled animals. Cryopreserved germplasm can be used in the future to produce live young for integration into other conservation projects, such as habitat restoration, captive breeding, and translocations; thus compensating for genetic losses or negative changes that would otherwise be permanent. Although hundreds of cryopreservation protocols for various aquatic species have been published, there are great difficulties in moving such research forward into applied conservation projects. Successful freezing of sperm in laboratories for research does not guarantee successful management and incorporation of genetic resources into conservation programs in reality. The goal of the present review is to provide insights and practical strategies to apply germplasm repositories as a real-world tool to assist conservation of imperiled aquatic species. Live-bearing (viviparous) fishes are used as models herein to help explain concepts because they are good examples for aquatic species in general, especially small-bodied fishes. Small live-bearing fishes are among the most at-risk fish groups in the world, and need urgent conservation attention. However, development of germplasm repositories for small live-bearing fishes is challenged by their unusual reproductive characteristics, such as formation of sperm bundles, initiation of spermatozoa motility in an isotonic environment, internal fertilization and gestation, and the bearing of live young. The development of germplasm repositories for goodeids and Xiphophorus species can provide examples for addressing these challenges. Germplasm repositories must contain multiple basic components, including frozen samples, genetic assessment and information systems. Standardization and process generalization are important strategies to help develop reliable and efficient repositories. An ideal conservation or recovery program for imperiled species should include a comprehensive approach, that combines major concerns such as habitat (by restoration projects), population propagation and maintenance (by captive breeding or translocation projects), and preservation of genetic diversity (by repository projects). In this context, strong collaboration among different sectors and people with different expertise is a key to the success of such comprehensive programs.

Sperm handling in aquatic animals for artificial reproduction

Artificial reproduction involves collection and handling of gametes in a way that secures their quality and maximizes the fertilization outcome. In addition to initial sperm quality, numerous steps can affect the final result of fertilization, from the sperm collection process until gamete mixing (or co-incubation) when the spermatozoon enters or fuses with the oocyte. In this review, we summarize the whole process of sperm handling, from collection until fertilization for fish, penaeid shrimp, bivalve mollusks and marine mammals. To obtain sperm from captive animals, techniques vary widely across taxa, and include stripping by abdominal massage or testis surgical removal in fish, spermatophore collection in penaeid shrimps, gonadal scarification or temperature shock in bivalve mollusks, and voluntary collection via positive reinforcement in mammals. In most cases, special care is needed to avoid contamination by mucus, seawater, urine, or feces that can either activate sperm motility and/or decrease its quality. We also review techniques and extender solutions used for refrigerated storage of sperm across the aforementioned taxa. Finally, we give an overview of the different protocols for in vivo and in vitro fertilization including activation of sperm motility and methods for gamete co-incubation. The present study provides valuable information regarding breeder management either for animal production or species conservation.

Opportunities and challenges related to the implementation of sperm cryopreservation into breeding of salmonid fishes

The main aim of the present review is to present the opportunities and challenges associated with the application of cryopreserved sperm, which may improve the breeding of salmonid fishes. Cryopreservation of sperm has been used as a strategy for the conservation of biodiversity of fishes populations, the preservation of sperm from the most valuable breeding individuals and facilitate transportation of genomes, and providing a biological source of sperm regardless of the synchronisation of the maturity of broodstocks. Cryopreserved sperm can be used for the genetic improvement of salmonid fishes based on the programs of individual crossing of selected males with individual females. However, these opportunities have not yet been fully implemented at the conditions of hatchery practice. Despite the significant progress concerning the standardization of cryopreservation procedures, there are still more challenges than opportunities related to the implementation of sperm cryopreservation into breeding of salmonid fishes. The main challenge concerns the scaling up of the method towards fulfilling the requirements of fishes-breeders, in particular mass production of eyed eggs and fry. The present review shows knowledge gaps that should be considered in further studies, including development of methods to obtain sufficient amounts of sperm from numerous species of salmonids, scaling up the methods towards cryopreservation of high volumes of sperm and towards thawing high number of straws, and optimizing artificial fertilization in which oocytes are fertilized with high numbers of frozen/thawed sperm. Moreover, the implementation of technologies into hatchery practice will require special consideration to counteract the risk of sperm infection and its transmission to offsprings during cryopreservation and storage in liquid nitrogen.

Workshop report: Cryopreservation of aquatic biomedical models

The genetic resources of aquatic biomedical model organisms are the products of millions of years of evolution, decades of scientific development, and hundreds of millions of dollars of research funding investment. Genetic resources (e.g., specific alleles, transgenes, or combinations) of each model organism can be considered a form of scientific wealth that can be accumulated and exchanged, typically in the form of live animals or germplasm. Large-scale maintenance of live aquatic organisms that carry these genetic resources is inefficient, costly, and risky. In situ maintenance may be substantially enhanced and backed up by combining cryopreserved germplasm repositories and genetic information systems with live animal culture. Unfortunately, cryopreservation has not advanced much beyond the status of an exploratory research for most aquatic species, lacks widespread application, and methods for successful cryopreservation remain poorly defined. For most aquatic species biological materials other than sperm or somatic cells are not comprehensively banked to represent and preserve a broad range of genetic diversity for each species. Therefore, new approaches and standardization are needed for repository-level application to ensure reproducible recovery of cryopreserved materials. Additionally, development of new technologies is needed to address preservation of novel biological materials, such as eggs and embryos of aquatic species. To address these goals, the Office of Research Infrastructure Programs (ORIP) of the National Institutes of Health (NIH) hosted the Cryopreservation of Aquatic Biomedical Models Workshop on January 7 to 8, 2017, in conjunction with the 8th Aquatic Animal Models of Human Disease Conference in Birmingham, Alabama. The goals of the workshop were to assess the status of germplasm cryopreservation in various biomedical aquatic models and allow representatives of the scientific community to develop and prioritize a consensus of specific actionable recommendations that will move the field of cryopreservation of aquatic resources forward. This workshop included sessions devoted to new approaches for cryopreservation of aquatic species, discussion of current efforts and approaches in preservation of aquatic model germplasm, consideration of needs for standardization of methods to support reproducibility, and enhancement of repository development by establishment of scalable high-throughput technologies. The following three broad recommendations were forwarded from workshop attendees: 1: Establish a comprehensive, centralized unit ("hub") to programmatically develop training for and documentation of cryopreservation methods for aquatic model systems. This would include development of species-specific protocols and approaches, outreach programs, community development and standardization, freezing services and training of the next generation of experts in aquatic cryopreservation. 2: Provide mechanisms to support innovative technical advancements that will increase the reliability, reproducibility, simplicity, throughput, and efficiency of the cryopreservation process, including vitrification and pipelines for sperm, oocytes, eggs, embryos, larvae, stem cells, and somatic cells of all aquatic species. This recommendation encompasses basic cryopreservation knowledge and engineering technology, such as microfluidics and automated processing technologies. 3: Implement mechanisms that allow the various aquatic model stock centers to increase their planning, personnel, ability to secure genetic resources and to promote interaction within an integrated, comprehensive repository network for aquatic model species repositories.

The Role of Reproductive Sciences in the Preservation and Breeding of Commercial and Threatened Teleost Fishes

The teleost fishes are the largest and most diverse vertebrate group, accounting for nearly half of all known vertebrate species. Teleost fish exhibit greater species diversity than any other group of vertebrates and this is reflected in the unique variety of different reproductive strategies displayed by fish. Fish have always been an important resource for humans worldwide, especially as food. While wild capture fisheries have historically been the main source of fish, the farming of fish (aquaculture) is increasingly becoming the more dominant source of food fish, and is predicted to account for 60% of total global fish production by 2030.Fishes are increasingly threatened by a wide range of anthropogenic impacts, including loss of habitat, pollution, invasive species and over-exploitation. In addition, climate change, especially the consequences of global warming, can impact fish at all levels of biological organization from the individual to the population level, influencing both physiological and ecological processes in a variety of direct and indirect ways. As such, there is an urgent need to protect and conserve the huge genetic diversity offered by this diverse vertebrate group, not just as a source of genes for contemporary breeding and for protection against the consequences of climate change and disease, but also as part of our national heritage. While the cryopreservation of reproductive cells is a means of achieving these objectives, currently only fish sperm can be successfully frozen. Due to their large size, large yolk compartment, low membrane permeability and high chilling sensitivity, successful and reproducible protocols for the cryopreservation of fish oocytes and embryos still remains elusive. However, significant advances have been made in the cryopreservation of primordial germ cells as an alternative means of conserving both paternal and maternal genomes. Although more research needs to be carried out on how these cells can be optimally applied to emerging reproductive technologies, including transplantation techniques and surrogate broodstock technologies, the successful cryopreservation of fish germ cells, and the establishment of genetic resource banks, offers the possibility of both conserving and restoring threatened species. Further, current and future conservation efforts need to consider the impact of climate change in both in situ conservation and reintroduction efforts.In conclusion, it is anticipated that the successful cryopreservation of fish germplasm will result in a range of economic, ecological and societal benefits. In partnership with emerging assisted reproductive technologies, the successful cryopreservation of fish germplasm will lead to more efficient reproduction in aquaculture, assist selective breeding programmes, and be of crucial importance to future species conservation actions.

Design and Cost Analysis of a Self-contained Mobile Laboratory for Commercial-scale Aquatic Species Cryopreservation

Although aquatic species cryopreservation protocols have been studied around the world over the past 60 yr., germplasm repository development efforts and commercialization have begun only recently. The goal of this project was to develop a self-contained mobile laboratory for on-site high-throughput cryopreservation of aquatic species. The objectives of this study were to: (1) identify how a mobile laboratory would function in different operational scenarios, (2) customize an enclosed cargo trailer to function as a mobile laboratory, (3) evaluate the laboratory layout and ability of cryopreservation equipment to operate from generator power, and (4) document the investment costs for private and public groups to integrate a mobile laboratory into an existing cryopreservation facility at three levels of automation and estimate the total cost per trip based on hypothetical assumptions for two scenarios (aquaculture production and repository development). There were three operational designs identified for the mobile laboratory: (1) self-contained work inside the unit using generator power, (2) work inside the unit using external facility power, and (3) using the equipment inside of a host facility. The investment costs for a base-level mobile laboratory ranged between US$5670 and US$5787 for private groups and between US$5208 and US$5315 for public groups. With the addition of a range of automated processing equipment, total investment costs ranged from US$13,616 to US$103,529 for private groups and US$12,494 to US$94,891 for public groups. The total cost per trip to cryopreserve sperm of 59 blue catfish, Ictalurus furcatus, males to produce 6300 0.5-mL French straws was estimated to range from US$6089 to US$14,633 for private and between US$5703 and US$16,938 for public groups depending on the level of automation. Total cost per trip to cryopreserve sperm of 500 males of five different species in the genus Xiphophorus to produce 641 0.25-mL French straws was estimated to range from US$6653 to US$7640 for private and US$7582 to US$8088 for public groups depending on level of automation. Overall, a commercial-scale mobile laboratory was developed that can assist current germplasm activities and support future repository and industry development, and the layout information provided can help others to design and build comparable units.

Addressing Reproducibility in Cryopreservation, and Considerations Necessary for Commercialization and Community Development in Support of Genetic Resources of Aquatic Species

For the past six decades a repeated cycle of developing new cryopreservation protocols or simply reinventing them to counteract a lack of reproducibility has led to hundreds of published studies that have offered little to the establishment of a genetic resources community for aquatic species. This has hampered repository development and inhibited industrial application. Most protocols were developed without standardized approaches, leading to irreproducible studies and questionable or meaningless comparisons. Thus cryopreservation of germplasm in aquatic species would greatly benefit from strategies to facilitate reproducibility. Our objectives were to: (1) identify major sources of irreproducibility across research, small-scale, repository, and commercial-scale development levels, (2) provide recommendations to address reproducibility challenges, and (3) offer suggestions on how researchers can directly influence commercial development and application of cryopreservation research. Sources of irreproducibility include lack of standardized procedural approaches, lack of standardized terminology, and lack of reporting guidelines. To address these challenges, we propose implementation of standard operating procedures (SOP), support of stock centers and internet content for development of training programs, and strengthening of the role of scientific journals and reviewers in reducing the frequency of irreproducible outcomes. Reproducibility is the foundation for quality management programs and product reliability, and therefore standardization is necessary to assure efficient transition to commercial-scale application and repository development. Progress can only be possible through community-based approaches focused on coalescence and consensus of disparate groups involved in aquatic species cryopreservation and management of genetic resources.

Production of live young with cryopreserved sperm from the endangered livebearing fish Redtail Splitfin (Xenotoca eiseni, Rutter, 1896)

Previous studies of sperm cryopreservation of livebearing fish have been limited to two genera within the family Poeciliidae. The goal of the present study was to investigate the feasibility to produce live young of livebearing goodeids (family Goodeidae) with cryopreserved sperm, using aquarium-trade populations of the endangered species Redtail Splitfin (Xenotoca eiseni, Rutter, 1896). Reproductive condition of females was evaluated by histological categorization of ovarian development. A total of 117 females were inseminated with cryopreserved sperm, 81 were inseminated with fresh sperm, 27 were mixed with males for natural breeding, and 30 were maintained without males or insemination. Histological images of 34 mature females indicated 68% of ovaries had primary- or secondary-growth oocytes, and 32% had ovulated eggs. Ovarian development had no significant relationship (P =  0.508) with body wet weight, but had a relationship (P <  0.001) with ovary weight and gonadosomatic index. Sperm cells were observed within ovaries that were fixed at 12 h after insemination with fresh sperm. A total of 29 live young were produced from two females inseminated with thawed sperm (8% post-thaw motility with HBSS300 as extender, 20 min incubation in 15% DMSO, cooling rate at 10 °C/min, and thawing at 40 °C for 7 s), 12 were produced from two females with fresh sperm (1%-20% motility), 41 were produced from five naturally spawned females, and no live young were produced from the female-only group. This study provides a foundation for establishment of germplasm repositories for endangered goodeids to assist conservation programs.

Cryopreservation of sperm bundles (spermatozeugmata) from endangered livebearing goodeids

More than half of fishes in the family Goodeidae are considered to be endangered, threatened, or vulnerable. Sperm cryopreservation is an effective tool for conserving genetic resources of imperiled populations, but development of protocols with livebearing fishes faces numerous challenges including the natural packaging of sperm into bundles. In this study the cryopreservation of sperm bundles (spermatozeugmata) of three goodeids species was evaluated. Sperm quality was evaluated by activation with NaCl-NaOH solution (at 300 mOsmol/kg and pH 11.8), and analysis of dissociable bundles and dissociation duration. Using Redtail Splitfin (Xenotoca eiseni) as a model, the effects of cryoprotectants (dimethyl sulfoxide, methanol, and glycerol) with different concentrations (5-15% v/v %), equilibration exposure times (1-60 min), cooling rates (5-40 °C/min), concentrations (4 × 10⁴-4 × 10⁶ bundles/ml), buffers (HBSS, PBS and NaCl), and buffer osmolalities (200-400 mOsmol/kg) were investigated. After cooling and thawing, sperm bundles maintained their packed form. A specific protocol was developed (10% dimethyl sulfoxide, 20-min equilibration, 10 °C/min cooling rate, 4 × 10⁶ bundles/ml, and 300 mOsmol/kg HBSS). This protocol yielded 89 ± 5% of post-thaw dissociable bundles with 209 ± 10 s of dissociation duration for X. eiseni, 96 ± 9% with 814 ± 14 s for Blackfin Goodea (Goodea atripinni), and 66 ± 2% with 726 ± 25 s for Striped Goodeid (Ataeniobius toweri). This is the first study of cryopreservation of sperm within bundles for livebearing fishes and provides a basis for establishment of germplasm repositories for goodeids and other livebearers.

Survival of Bacterial and Parasitic Pathogens from Zebrafish (Danio rerio) After Cryopreservation and Thawing

Cryopreservation is a common method used to preserve the sperm of various animal species, and it is widely used with zebrafish (Danio rerio). As with other animals, there is a possibility of paternal pathogen transmission through sperm. We evaluated the ability of five common and important pathogens of zebrafish to survive cryopreservation as used with zebrafish sperm and freezing without cryopreservant. We evaluated Mycobacterium chelonae, Mycobacterium marinum, and Edwardsiella ictaluri, each originally isolated from zebrafish, eggs of Pseuodocapillaria tomentosa, and spores of Pseudoloma neurophilia. Each mycobacterial isolate showed relatively minimal reduction in survival after freezing and thawing, particularly when subjected to cryopreservation. E. ictaluri also showed survival after cryopreservation, but exhibited a several log reduction after freezing at -80°C without cryopreservant. With P. neurophilia, two separate experiments conducted 3 years apart yielded very similar results, showing some, but reduced, survival of spores by using three different viability assays: SYTOX stain, Fungi-Fluor stain, and presence of a spore vacuole. Eggs of P. tomentosa showed no survival based on larvation of eggs when subjected to either freezing method. Given that four of the five pathogens exhibited survival after cryopreservation, we recommend that sperm samples or donor male zebrafish fish be tested for pathogens when sperm are to be stored by using cryopreservation.

A Strategy for Sperm Cryopreservation of Atlantic Salmon, Salmo salar, for Remote Commercial-scale High-throughput Processing

Sperm cryopreservation is an essential tool for long-term storage of genetic resources for aquaculture fishes. The goal of this study was to develop an efficient and streamlined protocol for high-throughput processing for sperm cryopreservation in Atlantic salmon, Salmo salar. The objectives were to evaluate: 1) osmolality of blood serum for determining extender osmolality; 2) effects of extenders for fresh sperm dilution and refrigerated storage; 3) effects of methanol and dimethyl sulfoxide (DMSO) on fresh sperm motility, and 4) motility and fertility after thawing. In this study, sperm samples were collected at a hatchery site in Canada, and shipped to a freezing site located 2200 miles (3550 km) away in the United States. Evaluation of three extenders indicated that Mounib solution was suitable for diluting dry sperm for sample processing. Ten percent of methanol or DMSO was less toxic to sperm cells than was 15% within 30 min. Further testing with methanol at 5, 10, and 15%, and sperm solution:extender dilutions (v:v) of 1:1, 1:3, 1:19 (at concentrations of ~5×10⁷; 3×10⁸, and 1×10⁹ cells/mL) indicated that methanol at 5% and 10% showed less toxicity to fresh sperm within 1 hr at sperm: extender dilutions of 1:1 and 1:3. Post-thaw motility of sperm cryopreserved with 10% methanol was significantly higher than that with 10% DMSO, and fertility reflected those results (0-1% in DMSO vs. 38-55% in methanol). Further evaluation of sperm cryopreservation with 10 and 15% methanol at sperm dilution ratios of 1:1, 1:3, 1:19 indicated post-thaw motility in 10% methanol was significantly higher than that in 15% methanol, and post-thaw fertility in 10% methanol at 1:1 and 1:3 dilution ratios had fertilization rates similar to that of fresh sperm controls. Sperm samples from 12 males cryopreserved with 10% methanol showed male-to-male variation in post-thaw motility (0-36%). Overall, a simplified standard protocol was established for cryopreservation of shipped sperm of Atlantic salmon using extender without egg yolk and yielded satisfactory post-thaw motility and fertilization rates. This procedure can be readily adopted by aquaculture facilities to take advantage of high-throughput cryopreservation capabilities at remote service centers. Most importantly, this approach lays the groundwork for an alternative commercial model for commercial-scale production, quality control and development of industrial standards. Control of male variability and sperm quality remain important considerations for future work.

Changes to Extender, Cryoprotective Medium, and In Vitro Fertilization Improve Zebrafish Sperm Cryopreservation

Sperm cryopreservation is a highly efficient method for preserving genetic resources. It extends the reproductive period of males and significantly reduces costs normally associated with maintenance of live animal colonies. However, previous zebrafish (Danio rerio) cryopreservation methods have produced variable outcomes and low post-thaw fertilization rates. To improve post-thaw fertilization rates after cryopreservation, we developed a new extender and cryoprotective medium (CPM), introduced quality assessment (QA), determined the optimal cooling rate, and improved the post-thaw in vitro fertilization process. We found that the hypertonic extender E400 preserved motility of sperm held on ice for at least 6 h. We implemented QA by measuring sperm cell densities with a NanoDrop spectrophotometer and sperm motility with computer-assisted sperm analysis (CASA). We developed a CPM, RMMB, which contains raffinose, skim milk, methanol, and bicine buffer. Post-thaw motility indicated that the optimal cooling rate in two types of cryogenic vials was between 10 and 15°C/min. Test thaws from this method produced average motility of 20% ± 13% and an average post-thaw fertilization rate of 68% ± 16%.

Quality evaluation of sperm from livebearing fishes: Standardized assessment of sperm bundles (spermatozeugmata) from Xenotoca eiseni (Goodeidae)

Standardized evaluation of sperm quality is essential for research, commercial-scale cryopreservation, and induced spawning. However, standardized methods for evaluation of sperm bundles (spermatozeugmata or spermatophores) have not been established. The purpose of the present study was to use Redtail Splitfin (Xenotoca eiseni) as a model for freshwater livebearing fishes to establish initial standardized methods to collect sperm bundles, and quantitatively and qualitatively evaluate quality-related attributes. No sperm or sperm bundles were able to be collected by stripping. Testes were removed, rinsed, weighed, placed in 50 μL of buffer solution on a glass slide, and crushed gently 3-5 times with angled spade-tip forceps. Sperm bundles were released into the buffer solution and collected with a pipette into 1.5-mL centrifuge tubes. To quantify size and shape, images of bundles were captured with a CCD camera connected to a microscope, and measured with computer software. There was no significant correlation between body wet weight and major bundle axis length (P = 0.6759), minor axis length (P = 0.5658), average axis length (P = 0.5869), aspect ratio (P = 0.7839), and observed area (P = 0.5727). The concentrations of sperm bundles, estimated with the three methods (Makler^® counting chamber, a hemocytometer, and direct counting) were significantly different (P < 0.0001). Hemocytometers were suitable for estimation of bundles from X. eiseni. To evaluate activation of sperm, bundles were viewed with a microscope, and classified into one of five phases by evaluating morphology of the bundles and motion of sperm within the bundles as Phase 0 through Phase 4 that represented early through late activation stages. The frequencies and duration of each activation phase were used to evaluate dissociation of sperm bundles and motility capability of sperm within the bundles. Within 180 min of activation, all five phases were observed. Overall, this study for the first time established standardized methods to collect and evaluate quality-related attributes of sperm bundles. These standardized evaluations provide a basis for further modification, standardization, and generalization, which are useful in research on livebearing fishes involving male gametes, such as studies on cryopreservation, artificial insemination, and in development of germplasm repositories for imperiled species including goodeids.

Challenges in Development of Sperm Repositories for Biomedical Fishes: Quality Control in Small-Bodied Species

Quality control (QC) is essential for reproducible and efficient functioning of germplasm repositories. However, many biomedical fish models present significant QC challenges due to small body sizes (<5 cm) and miniscule sperm volumes (<5 μL). Using minimal volumes of sperm, we used Zebrafish to evaluate common QC endpoints as surrogates for fertilization success along sequential steps of cryopreservation. First, concentrations of calibration bead suspensions were evaluated with a Makler^® counting chamber by using different sample volumes and mixing methods. For sperm analysis, samples were initially diluted at a 1:30 ratio with Hanks' balanced salt solution (HBSS). Motility was evaluated by using different ratios of sperm and activation medium, and membrane integrity was analyzed with flow cytometry at different concentrations. Concentration and sperm motility could be confidently estimated by using volumes as small as 1 μL, whereas membrane integrity required a minimum of 2 μL (at 1 × 10⁶ cells/mL). Thus, <5 μL of sperm suspension (after dilution to 30-150 μL with HBSS) was required to evaluate sperm quality by using three endpoints. Sperm quality assessment using a combination of complementary endpoints enhances QC efforts during cryopreservation, increasing reliability and reproducibility, and reducing waste of time and resources.

3-D printing provides a novel approach for standardization and reproducibility of freezing devices

Cryopreservation has become an important and accepted tool for long-term germplasm conservation of animals and plants. To protect genetic resources, repositories have been developed with national and international cooperation. For a repository to be effective, the genetic material submitted must be of good quality and comparable to other submissions. However, due to a variety of reasons, including constraints in knowledge and available resources, cryopreservation methods for aquatic species vary widely across user groups which reduces reproducibility and weakens quality control. Herein we describe a standardizable freezing device produced using 3-dimensional (3-D) printing and introduce the concept of network sharing to achieve aggregate high-throughput cryopreservation for aquatic species. The objectives were to: 1) adapt widely available polystyrene foam products that would be inexpensive, portable, and provide adequate work space; 2) develop a design suitable for 3-D printing that could provide multiple configurations, be inexpensive, and easy to use, and 3) evaluate various configurations to attain freezing rates suitable for various common cryopreservation containers. Through this approach, identical components can be accessed globally, and we demonstrated that 3-D printers can be used to fabricate parts for standardizable freezing devices yielding relevant and reproducible cooling rates across users. With standardized devices for freezing, methods and samples can harmonize into an aggregated high-throughput pathway not currently available for aquatic species repository development.

Standardized Assessment of Thin-film Vitrification for Aquatic Species

Ultra-rapid cooling under the appropriate conditions will produce vitrification, a glass-like state used to cryopreserve small sample volumes, but there are a number of major technical drawbacks impeding application of vitrification to germplasm of aquatic species. These include a lack of suitable devices, and poor reproducibility and comparability among studies due to a lack of standardization. We used 3-dimensional (3-D) printing to produce a viewing pedestal coupled with a classification system to rapidly assess frozen film quality of vitrification loops. Classification time declined with practice from 2.1 ± 0.3 sec to 1.5 ± 0.2 sec (after 200 assessments), and assessments were consistently made in < 2.5 sec. Classifications should be reported with representative images allowing harmonization for quality control. This approach permits rapid classification and can be applied for development of methods including evaluation of vitrification solution components, concentrations of solution and target cells, and configurations and volumes of new devices. Future studies should address the custom fabrication of 3-D printed vitrification devices for use with aquatic species and other applications.

Amine reactive dyes: an alternative to estimate membrane integrity in fish sperm cells

Fluorescent dyes that binds irreversibly to cellular amines, come in several available emission spectra, and do not poses health concerns were used to evaluate membrane integrity in fish sperm cells. The objectives of the present study were to determine: (1) a working dye concentration for fish sperm samples, and (2) if the traditional propidium iodide/SYBR-14 staining combination was comparable with the amine reactive dye (ARD) methods at identifying cell populations with intact and compromised membranes after sperm activation, refrigerated storage, and exposure to cryoprotectant and surfactant. Zebrafish (Danio rerio) sperm were obtained by stripping, and pooled samples (in triplicate) were used in all tests. Six dilutions of the amine dye (ranging from 0.625 to 0.02 μL/mL) were evaluated, and compared with the traditional staining protocol. A concentration of 0.5 μL/mL ARD was selected to be used in subsequent assays. Sperm suspensions were activated with deionized water to simulate urine contamination. After 10 sec, osmolality was increased to stop activation, and the procedure was repeated in 10-sec intervals until the sperm remained activated for 120 consecutive sec; membrane integrity was analyzed at each time interval. For the storage assay, sperm suspensions were prepared in Hanks' balanced salt solution at 302 mOsm/kg osmolality (HBSS302), HBSS354 and HBSS402, and evaluated every 2 hr for 8 hr, and every 24 hr for 72 hr. Cryoprotectant toxicity was tested by diluting sperm suspensions in HBSS340 with methanol at 5, 10 and 15% final concentrations. Surfactant toxicity was tested by diluting sperm suspensions in HBSS354 with Triton X-100 at 0.2, 0.15 and 0.1 mM final concentrations. In each toxicity assay, membrane integrity was tested every 20 min for 80 min. The number of membrane-intact cells significantly decreased across time in all treatments (p < 0.05). Significant differences between staining protocols were observed after activation and after exposure to methanol at 10 and 15%, and to Triton X-100 (p < 0.05). The average difference, however, was minor (between 1 and 6% in average) in relation to the typical values used for decision making based on this assay. Results showed that this method has the potential to contribute greatly to the standardization of cryopreservation in aquatic species.