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

An Open-Hardware Insemination Device for Small-Bodied Live-Bearing Fishes to Support Development and Use of Germplasm Repositories

Small-bodied live-bearing fishes attract broad attention because of their importance in biomedical research and critical conservation status in natural habitats. Artificial insemination is an essential process to establish hybrid lines and for the operation of sperm repositories. The existing mouth-pipetting technique for artificial insemination of live-bearing fishes has not been substantially upgraded since the first implementation in the 1950s. The goal of this work was to develop a standardized artificial inseminator device (SAID) to address issues routinely encountered in insemination by mouth-pipetting, including lack of reproducibility among different users, difficulty in training, and large unreportable variation in sample volume and pressure during insemination. Prototypes of the SAID were designed as relatively inexpensive ( 0.99) between the piston position and volume. Pressure generation from eight mouth-pipetting operators and SAID prototypes were assessed by pressure sensors. The pressure control by SAID was superior to that produced by mouth-pipetting, yielding lower pressures (31−483 Pa) and smaller variations (standard deviation <11 Pa). These pressures were sufficient to deliver 1−5 μL of fluid into female reproductive tracts yet low enough to avoid physical injury to fish. Community-level enhancements of the SAID prototype could enable standardized insemination with minimal training and facilitate the participation of research communities in the use of cryopreserved genetic resources.

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.

Opportunities and Limitations for Reproductive Science in Species Conservation

Reproductive science in the context of conservation biology is often understood solely in terms of breeding threatened species. Although technologies developed primarily for agriculture or biomedicine have a potentially important role in species conservation, their effectiveness is limited if we regard the main objective of animal conservation as helping to support populations rather than to breed a small number of individuals. The global threats facing wild species include the consequences of climate change, population growth, urbanization, atmospheric and water pollution, and the release of chemicals into the environment, to cite but a few. Reproductive sciences provide important and often unexpected windows into many of these consequences, and our aim here is both to demonstrate the breadth of reproductive science and the importance of basic knowledge and to suggest where some of the insights might be useful in mitigating the problems. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

3-D Printed Customizable Vitrification Devices for Preservation of Genetic Resources of Aquatic Species

Sperm vitrification as an alternative approach to conventional cryopreservation (equilibrium freezing) allows quick and low-cost sample preservation and is suitable for small-bodied aquatic species with miniscule testis, fieldwork at remote locations, and small-scale freezing for research purposes. The goal of this present study was to develop operational prototypes of 3-dimensional (3-D) printed vitrification devices with innovative components that can provide comprehensive functionalities for practical repository development for aquatic species. The design featured an elongated loop to suspend a thin film of sperm sample in cryoprotectant, a retractable sleeve to protect the vitrified samples and allow permanent labeling, a handle to facilitate processing and storage, and a shaft with annular grooves to guide positioning of the protective retractable sleeve. To span a wide range of sample capacities and configurations, a total of 39 different configurations (3 loop lengths ×13 loop heights) were fabricated by 3-D printing with the thermoplastics polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). A total of 86 devices were fabricated with ABS filament with a print failure rate of 9%, and 97 devices were fabricated with PLA filament with a failure rate of 20%. Major types of printing failures included disconnected loops, insufficient build surface adhesion, stringing, and inconsistent extrusion. The sample volume capacity ranged from 1-47 μL and had linear relationships to the loop lengths and layer numbers. Vitrified samples were observed in 10-mm and 15-mm loops fabricated with PLA and ABS but not in 20-mm loops. This study demonstrated the feasibility of development of standardized low-cost ($0.05 material cost) devices fabricated by 3-D printing with practical functions including vitrification, volume control, labeling, protection, and storage within conventional systems. These prototypes can be further developed, standardized, and used to assist development of germplasm repositories to protect the genetic resources of aquatic species by user groups such as breeders, hatcheries, aquariums, and researchers.

The role of alkalinization-induced Ca2+ influx in sperm motility activation of a viviparous fish Redtail Splitfin (Xenotoca eiseni)

Mechanisms regulating sperm motility activation are generally known in oviparous fishes, but are poorly understood in viviparous species. The mechanism of osmotic-shock induced signaling for oviparous fishes is not suitable for viviparous fishes which activate sperm motility within an isotonic environment. In addition, the presence of sperm bundles in viviparous fishes further complicates study of sperm activation mechanisms. The goal of this study was to establish methodologies to detect intracellular Ca2+ signals from sperm cells within bundles, and to investigate the signaling mechanism of sperm activation of viviparous fish using Redtail Splitfin (Xenotoca eiseni) as a model. Motility was assessed by classification of bundle dissociation and computer-assisted sperm analysis, and intracellular Ca2+ was assessed using the fluorescent probe Fura-2 AM. Bundle dissociation and sperm motility increased with extracellular Ca2+ and pH levels. Intracellular Ca2+ signals were detected from sperm within bundles, and increased significantly with extracellular Ca2+ and pH levels. Major channel blockers known to inhibit Ca2+ influx (NiCl2, ruthenium red, GdCl3, SKF-96365, nimodipine, verapamil, methoxyverapamil, mibefradil, NNC 55-0396, ω-Conotoxin MVIIC, bepridil, and 2-APB) failed to inhibit Ca2+ influx, except for CdCl2, which partially inhibited the influx. We propose a novel mechanism for motility regulation of fish sperm: an alkaline environment in the female reproductive tract opens Ca2+ channels in the sperm plasma membrane without osmotic shock, and the Ca2+ influx functions as a second messenger to activate motor proteins controlling flagella movement.

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.