Sperm cryopreservation in guppies and black mollies--a generalized freezing protocol for livebearers in Poeciliidae

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.

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.

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.

2,2'-Dithiobis-pyridine induced reproductive toxicity in male guppy (Poecilia reticulata)

Metal pyrithiones (MePTs) are frequently used antifouling biocides in marine coatings. Their main degradation product, 2,2'-dithiobis-pyridine ((PS)₂), has been widely detected in seawater and may pose potential ecological risks. In the present study, sexually mature guppies (Poecilia reticulata) were exposed to (PS)₂ at concentrations of 0, 20, 200, and 2000 ng/L for 28 days to investigate its reproductive toxicity. The results showed that (PS)₂ significantly reduced testosterone (T) levels, spermatogenic cyst number and sperm motility, impeded spermatogenic cell differentiation in male guppies and delayed embryo development in females. These results indicated that (PS)₂ could cause reproductive toxicity in guppies. We also examined mRNA expression of indices involved in the hypothalamic-pituitary-gonadal axis and reproductive behaviors. We found that 200 and 2000 ng/L (PS)₂ decreased T synthesis by downregulating 17βHSD and CYP17 mRNA levels, and upregulating the mRNA level of CYP19a1a, which converted T to 17β-estradiol. (PS)₂ also upregulated GnRH1, FSHβ, LHβ, and LHR mRNA levels, a positive feedback regulation due to the decrease of T levels in male guppies. Furthermore, (PS)₂ significantly decreased CYP19a1b mRNA levels in all three exposure groups and thus reduced the display frequency of male guppies. This study was the first to report that (PS)₂ could induce reproductive toxicity, which would provide a basis for future assessment of its ecological risk.

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.

Activation of free sperm and dissociation of sperm bundles (spermatozeugmata) of an endangered viviparous fish, Xenotoca eiseni

Knowledge of sperm motility activation for viviparous fishes has been limited to study of several species in Poeciliidae, and the dissociation of sperm bundles is even less understood. The goal of this study was to use the endangered Redtail Splitfin (Xenotoca eiseni) as a model to investigate the activation of sperm from viviparous fishes by study of free sperm and spermatozeugmata (unencapsulated sperm bundles). The specific objectives were to evaluate the effects of: (1) osmotic pressure and refrigerated storage (4 °C) on activation of free sperm, (2) osmotic pressure, ions, and pH on dissociation of spermatozeugmata, and (3) CaCl₂ concentration and pH on sperm membrane integrity. Free sperm were activated in Ca²⁺-free Hanks' balanced salt solution at 81-516 mOsmol/kg. The highest motility (19 ± 6%) was at 305 mOsmol/kg and swim remained for 84 h. Glucose (300-700 mOsmol/kg), NaCl (50-600 mOsmol/kg), and KCl, MgCl₂, and MnCl₂ at 5-160 mM activated sperm within spermatozeugmata, but did not dissociate spermatozeugmata. CaCl₂ at 5-160 mM dissociated spermatozeugmata within 10 min. Solutions of NaCl-NaOH at pH 11.6 to 12.4 dissociated spermatozeugmata within 1 min. The percentage of viable cells had no significant differences (P = 0.2033) among different concentrations of CaCl₂, but it was lower (P < 0.0001) at pH 12.5 than at pH between 7.0 and 12.0. Overall, this study provided a foundation for quality evaluation of sperm and spermatozeugmata from livebearing fishes, and for development of germplasm repositories for imperiled goodeids.

The effects of osmolality on sperm quality in Jenynsia multidentata (Cyprinodontiformes: Anablepidae)

Sperm quality tests on fish are classically used for evaluating cryopreservation procedures, and they are also promising to assess aquatic toxicity and biomarkers of xenobiotic effects on reproduction. Osmotic shock from the storage medium is one of the main factors affecting sperm quality during evaluation. Thus, the objective of this study was to evaluate the effects of different osmolalities (240-460 mOsm/kg) for at least 4 days on the sperm quality parameters of the viviparous fish Jenynsia multidentata. The level of significance was (P < 0.05). The plasma osmolality of J. multidentata is 326 ± 3.9 mOsm/kg. The motility of fresh semen was higher in osmolalities of 280 and 300 mOsm/kg but did not differ between osmolalities from 240 to 320 mOsm/kg. Above 380 mOsm/kg, the motility observed was 0%. Over the time period studied motility increased with increasing osmolality, and the most constant and long-lasting rates were between 300 and 320 mOsm/kg. On the 4th day of evaluation, higher membrane integrity rates were observed between 280 and 360 mOsm/kg, higher mitochondrial membrane potential was observed between 300 and 460 mOsm/kg, and higher DNA integrity rates were observed between 260 and 380 mOsm/kg. Moreover, osmolalities ≥460 and ≤240 resulted in the lowest motility and DNA integrity levels. Over 4 days, the plasma membrane integrity was significantly lower at ≤260 and ≥400 mOsm/kg, and the mitochondrial membrane potential was significantly lower only in osmolalities ≤240 mOsm/kg. Therefore, we conclude that for sperm quality preservation in J. multidentata, an osmolality of 300-320 mOsm/kg of the most suitable diluent is necessary. Furthermore, we conclude that the storage of sperm in a hyposmotic (<260 mOsm/kg) or hyperosmotic (>400 mOsm/kg) solution affects not only motility but also other sperm quality parameters.

Production of F₁ offspring with vitrified sperm from a live-bearing fish, the green swordtail Xiphophorus hellerii

This study reports the first production of offspring with vitrified sperm from a live-bearing fish Xiphophorus hellerii. The overall goal of this study was to develop streamlined protocols for integration into a standardized approach for vitrification of aquatic species germplasm. The objectives were to (1) estimate acute toxicity of cryoprotectants, (2) evaluate vitrification solutions, (3) compare different thawing methods, (4) evaluate membrane integrity of post-thaw sperm vitrified in different cryoprotectants, and (5) evaluate the fertility of vitrified sperm. Nine cryoprotectants and two commercial vitrification additives were tested for acute toxicity and glass forming ability, alone and in combination. Two vitrification solutions, 40% glycerol (Gly) and 20% Gly+20% ethylene glycol (EG) in 500 mOsmol/kg Hanks' balanced salt solution (HBSS), were selected for vitrification of 10 μL sperm samples using inoculating loops plunged into liquid nitrogen. Samples were thawed at 24°C (one loop in 5 μL of HBSS or three loops in 500 μL of HBSS). Samples thawed in 500 μL were concentrated by centrifugation (1000 g for 5 min at 4°C) into 5 μL for artificial insemination. Offspring were produced from virgin females inseminated with sperm vitrified with 20% Gly+20% EG and concentrated by centrifugation.