Effects of methanol and developmental arrest on chilling injury in zebrafish (Danio rerio) embryos

Cooling of Siamese fighting fish Betta splendens (Teleostei, Osphronemidae) embryos at low temperatures

The Siamese fighting fish (Betta splendens) has great importance as an ornamental aquarium fish as well as laboratory model species. Due to its rapid development, a cooling-embryo protocol could provide some advantages in their transportation, embryonic synchronization, and optimization of hatcheries. In this context, this work aimed to develop a protocol to storage B. splendens embryos at two temperatures (5 and 14 °C), testing three cryoprotective solutions (S1: 0.5 M sucrose, 1.5 M methanol; S2: 0.25 M sucrose, 0.75 M methanol; and S3: 0.125 M sucrose, 0.375 M methanol) and evaluating the quality of the larvae obtained. Moreover, a method to isolate the embryos from the bubble nest constructed by the male and to incubate them without parental care was applied in this study. The cooling assays were done using embryos of 24-h-post-fertilization at 26 °C and the results demonstrated that it is possible to store these embryos deprived of cryoprotectants at 5 °C for at least 6-h without negative effects. Meanwhile, S2 and S3 were the most suitable solutions for its storage for 9-h at 5 °C or 24-h at 14 °C, obtaining 77% hatching and 52% normal larvae in the first case or 88% hatching and 81% larvae with mild abnormalities in the second one. Indeed, type and frequency of larval abnormalities were evaluated and, remarkably, a partial recovery was described on malformed larvae from embryo cooled at 14 °C. Finally, this work is the first report about the cooling of B. splendens embryos and establishes the conditions for further studies on this field with this species.

Cryopreservation and Laser Nanowarming of Zebrafish Embryos Followed by Hatching and Spawning

This study shows for the first time the ability to rewarm cryopreserved zebrafish embryos that grow into adult fish capable of breeding normally. The protocol employs a single injection of cryoprotective agents (CPAs) and gold nanorods (GNRs) into the yolk and immersion in a precooling bath to dehydrate the perivitelline space. Then embryos are encapsulated within CPA and GNR droplets, plunged into liquid nitrogen, cryogenically stabilized, and rewarmed by a laser pulse. Postlaser nanowarming, embryos (n = 282) exhibit intact structure by 1 h (40%), continued development after 3 h (22%), movement after 24 h (11%), hatching after 48 h (9%), and swimming after Day 5 (3%). Finally, from fish that survives till Day 5, two larvae are grown to adulthood and spawned, yielding survival comparable to an unfrozen control. Future efforts will focus on improving the survival to adulthood and developing methods to cryopreserve large numbers of embryos for research, aquaculture, and biodiversity preservation.

Development of a spermatogonia cryopreservation protocol for blue catfish, Ictalurus furcatus

Sustainability of channel catfish, Ictalurus punctatus ♀ × blue catfish, Ictalurus furcatus ♂ hybrid aquaculture relies on new innovative technologies to maximize fry output. Transplanting spermatogonial stem cells (SSCs) from blue catfish into channel catfish hosts has the potential to greatly increase gamete availability and improve hybrid catfish fry outputs. Cryopreservation would make these cells readily accessible for xenogenesis, but a freezing protocol for blue catfish testicular tissues has not yet been fully developed. Therefore, the objectives of this experiment were to identify the best permeating [dimethyl sulfoxide (DMSO), ethylene glycol (EG), glycerol, methanol] and non-permeating (lactose or trehalose with egg yolk or BSA) cryoprotectants, their optimal concentrations, and the best freezing rates (-0.5, -1.0, -5.0, -10 °C/min until -80 °C) that yield the highest number of viable type A spermatogonia cells. Results showed that all of these factors had significant impacts on post-thaw cell production and viability. DMSO was the most efficient permeating cryoprotectant at a concentration of 1.0 M. The optimal concentration of each cryoprotectant depended on the specific cryoprotectant due to interactions between the two factors. Of the non-permeating cryoprotectants, 0.2 M lactose with egg yolk consistently improved type A spermatogonia production and viability beyond that of the 1.0 M DMSO control. The overall best freezing rate was consistent at -1 °C/min, but similar results were obtained using -0.5 °C/min. Overall, we recommend cryopreserving blue catfish testicular tissues in 1.0 M DMSO with 0.2 M lactose and egg yolk at a rate of either -0.5 or -1 °C/min to achieve the best cryopreservation outcomes. Continued development of cryopreservation protocols for blue catfish and other species will make spermatogonia available for xenogenic applications and genetic improvement programs.

Cooling of pejerrey Odontesthes bonariensis (Teleostei, Atherinidae) embryos at sub-zero temperatures

Pejerrey fish (Odontesthes bonariensis) is a seasonal multiple spawner with great economic importance and an adequate species for Aquaculture. For these reasons, it is necessary to apply biotechnologies to optimize its reproduction in captivity. In this context, the aim of this work was to develop a cooling protocol for pejerrey embryos at sub-zero temperatures. Two cryoprotective solutions (CSs: S1 and S2), two cooling curves (a fast and a slow one) and two storage temperatures (-14 and -20 °C) were evaluated for 1 h. High percentages of embryo survival (80-100%) were obtained in all cases. In particular, for cooling at -14 °C, the most suitable protocol was the slow temperature decrease in combination with S1 (2.5 M methanol, 1.4 M Me2SO, 0.3 M sucrose, and 0.08 M NaCl). The hatching rate (86.67 ± 11.55%) and the larval survival observed did not differ from those of the control group, and about 30% of normal-looking larvae were obtained. Besides, the slow cooling was also the best way to reach -20 °C, obtaining a hatching rate of around 60%. However, all the larvae had different kind of malformations. Finally, in order to improve the results obtained at -20 °C, the CSs were incorporated into the embryos by microinjection. In this case, it was observed that the most convenient combination was the microinjection of S2 (same composition as S1 but without Me2SO) in the perivitelline space followed by rapid cooling. Although the hatching rate was not improved (67.93 ± 8.31%), the microinjection allowed to obtain at least 4.5% normal-looking larvae. These results showed that the cooling of pejerrey embryos at zub-zero temperatures was feasible. Moreover, the microinjection of cryoprotectants within the pejerrey O.bonariensis embryos was employed for the first time in this species.

Semen cryopreservation for the Mediterranean brown trout of the Biferno River (Molise-Italy): comparative study on the effects of basic extenders and cryoprotectants

This study was designed to optimize the semen freezing protocol of the native Mediterranean brown trout inhabiting the Molise rivers through two experiments: an in vitro analysis of the effects of two basic extenders combined with three cryoprotectants on post-thaw semen quality; and an in vivo test to assess the fertilization and hatching rate. Semen was diluted at a ratio of 1:3 in a freezing medium composed of a glucose extender (A) or mineral extender (B). Each basic component contained 10% dimethylsulfoxide, dimethylacetamide or methanol. The post-semen quality was evaluated considering motility, duration of motility, viability and DNA integrity. The basic extender and cryoprotectant were shown to have significant effects on these variables, and the best results were obtained using extender A or B combined with dimethylsulfoxide (P < 0.05). These freezing protocols were selected for fertilization trials in vivo. Fertilization and hatching rates were significantly higher in fresh semen. No significant differences were observed in frozen semen using extender A or B, although higher percentages of eyed eggs and hatching rates were recorded using extender A. According to our in vitro and in vivo results, the glucose-based extender and dimethylsulfoxide emerged as the best combination for an effective cryopreservation protocol for semen of this trout.

Cryobanking of aquatic species

This review is focused on the applications of genome cryobanking of aquatic species including freshwater and marine fish, as well as invertebrates. It also reviews the latest advances in cryobanking of model species, widely used by the scientific community worldwide, because of their applications in several fields. The state of the art of cryopreservation of different cellular types (sperm, oocytes, embryos, somatic cells and primordial germ cells or early spermatogonia) is discussed focusing on the advantages and disadvantages of each procedure according to different applications. A special review on the need of standardization of protocols has also been carried out. In summary, this comprehensive review provides information on the practical details of applications of genome cryobanking in a range of aquatic species worldwide, including the cryobanks established in Europe, USA, Brazil, Australia and New Zealand, the species and type of cells that constitute these banks and the utilization of the samples preserved.

STATEMENT OF RELEVANCE

This review compiles the last advances on germplasm cryobanking of freshwater and marine fish species and invertebrates, with high value for commercial aquaculture or conservation. It is reviewed the most promising cryopreservation protocols for different cell types, embryos and larvae that could be applied in programs for genetic improvement, broodstock management or conservation of stocks to guarantee culture production.

Cryoprotectant Toxicity: Facts, Issues, and Questions

High levels of penetrating cryoprotectants (CPAs) can eliminate ice formation during cryopreservation of cells, tissues, and organs to cryogenic temperatures. But CPAs become increasingly toxic as concentration increases. Many strategies have been attempted to overcome the problem of eliminating ice while minimizing toxicity, such as attempting to optimize cooling and warming rates, or attempting to optimize time of adding individual CPAs during cooling. Because strategies currently used are not adequate, CPA toxicity remains the greatest obstacle to cryopreservation. CPA toxicity stands in the way of cryogenic cryopreservation of human organs, a procedure that has the potential to save many lives. This review attempts to describe what is known about CPA toxicity, theories of CPA toxicity, and strategies to reduce CPA toxicity. Critical analysis and suggestions are also included.

Cooling of pirapitinga (Piaractus brachypomus) embryos stored at -10ºC

Cryopreservation has not been used successfully to preserve fish embryos, although chilling techniques have been used with good results. The aim of this study was to chill Piaractus brachypomus embryos at - 10°C for various storage times. Embryos at the following ontogenetic stages were used: blastoderm - 1.2 hours post-fertilization (hpf); epiboly - 5 hpf; blastopore closure - 8 hpf; and appearance of the optic vesicle - 13 hpf. One hundred embryos were selected from each ontogenetic stage and chilled at - 10°C for 6 or 10 h. The results were analysed using analysis of variance (ANOVA) and Tukey's test at a 5% significance level. A significantly greater number of completely developed live larvae were observed following embryonic treatment with a cryoprotectant solution that contained 17.5% sucrose and 10% methanol. There was no survival for embryos cooled at - 10°C in initial developmental stages (1, 2 and 5 h hpf). Furthermore, higher survival rates were observed when embryos were treated at more advanced developmental stages (8 and 13 hpf). Therefore, P. brachypomus embryos at the blastopore-closure (8 hpf) or appearance-of-optic-vesicle (13 hpf) stages should be used for embryo chilling protocols and chilling should be performed using a 17.5% sucrose with a 10% methanol solution at - 10°C for up to 6 h. The best results were obtained with 13-hpf and 8-hpf embryos and cooling at 6 h of storage.

Lipid content and composition during the oocyte development of two gorgonian coral species in relation to low temperature preservation

Our previous studies have suggested that chilling sensitivity of coral oocytes may relate to their relatively high lipid intracellular content and lipid composition. The distribution of lipids during the oocyte development was determined here for the first time in two gorgonian species (Junceella juncea and Junceella fragilis). The main lipid classes in the two gorgonian oocytes were total lipid, wax ester, triacylglycerol, total fatty acid, phosphatidylethanolamine and phosphatidylcholine. The results indicated that early stage oocytes of J. juncea and J. fragilis were found to have increased lipid content than late stage oocytes. The content of wax ester was significantly higher in the early stage oocytes of two gorgonian corals (51.0±2.5 and 41.7±2.9 µg/mm(3)/oocyte) than those of late stage oocytes (24.0±1.4 and 30.4±1.2 µg/mm(3)/oocyte, respectively). A substantial amount of phosphatidylethanolamine and total fatty acid was detected at each stage of oocyte development in two gorgonian ranges from 107 to 42 µg/mm(3)/oocyte and 106 to 48 µg/mm(3)/oocyte, whilst low levels of phosphatidylcholine were found in two gorgonian oocytes. The levels of total lipid in the late stage oocytes of J. juncea were significantly higher than those of J. fragilis. The observed differences may partially be related to different habitat preferences as higher lipid levels in J. juncea, a deeper-water coral species exposed to lower temperature seawater, might relate to adjustments of cell membranes in order to increase membrane fluidity.

Chilling curves for Piaractus mesopotamicus (Holmberg, 1887) embryos stored at −8°C

The present study investigates the effect of different slow chilling curves on the storage of pacu (Piaractus mesopotamicus) embryos submitted to chilling at −8°C. Embryos at the blastopore closure stage were divided into two groups: G1 – embryos exposed to cryoprotectant solution containing methanol (10%) and sucrose (0.5 M), treated as follows: (T1) taken directly from room temperature to the refrigerator without being submitted to the curve; (T2) chilling curve of 0.5°C/min; and (T3) chilling curve of 1°C/min; and G2 – the cryoprotectant solution alone was submitted to these same temperatures, receiving the embryos only after temperature had decreased, corresponding to treatments T4, T5 and T6, respectively. Treatments were kept at −8°C for a period of 6 h. Embryo development was evaluated for each treatment, with six replicates in an entirely randomized design. Survival among embryos not submitted to refrigeration was 94.3 ± 8.05%. Percentage of total larvae (TL) and addled eggs (AE) did not differ statistically between the groups, although percentage of swimming larvae (SL) exhibited higher values in G1 for the 1°C/min curve. Furthermore, when comparing the three chilling curves, a decrease of 1°C/min resulted in the highest TL percentage (90.85%), followed by the 0.5°C/min curve (78.52%). Thus, the use of 1°C/min chilling curves is recommended for P. mesopotamicus embryos stored for 6 h at −8°C.

The effect of chilling and cryoprotectants on hard coral (Echinopora spp.) oocytes during short-term low temperature preservation

Understanding chilling sensitivity and chilling injury of coral oocytes, in the presence and absence of a cryoprotectant, is important in developing cryopreservation protocols, as well as for short-term storage and transport (e.g., for species conservation). The objective of this study was to investigate the chilling sensitivity of hard coral (Echinopora spp.) oocytes and the effectiveness of methanol (as a cryoprotectant) in protecting these oocytes during short-term, low temperature preservation. Oocytes were exposed to 0.5, 1, or 2 m methanol at 5, 0, or -5 °C for 1, 2, 4, 6, 8, 16, or 32 h, and their quality determined based on adenosine triphosphate (ATP) content. Methanol at 0.5 m was the most effective means to reduce chilling-induced reduction in ATP concentrations. Coral oocytes can be stored at room temperature for 4 h in filtered nature seawater with no detrimental effect on oocyte quality; however, in the present study, oocyte survival was extended for 8 h by addition of methanol in low concentrations (0.5 or 1 m) at low temperatures (5 and 0 °C). These findings should enhance conservation efforts and facilitate low-temperature transport of endangered and threatened coral species.

Cooling of pacu (Piaractus mesopotamicus) embryos at various stages of development for 6 or 10 hours

The objective of this research was to verify the effects of cooling embryos of pacu, Piaractus mesopotamicus, in four stages of development during two stocking periods. The stages of embryo development were at: blastoderm, ∼ 64 cells-1.4 h after fertilization (haf); 25% of the epiboly movement--5.2 haf; blastoporous closing--8.0 haf; and optical vesicle appearing--13.3 haf. Embryos were exposed to a cryoprotectant solution containing methanol (10%) and sucrose (0.5 M). Thereafter, embryos were submitted to a cooling curve until they reached -8 °C, and then kept cooled for 6 or 10 h. In addition, for each stage of embryonic development, a control group with uncooled embryos was used to compare hatching rates. The total number of larvae from the first two stages of ontogenetic development (1.4 and 5.2 haf) was lower compared to the other stages (0.0 and 8.0 haf). There was no significant difference between stages 8.0 and 13.3 haf for the total number of larvae (49.9 ± 6.7% and 55.2 ± 6.7%, respectively). Embryo diameter varied according to embryonic stage, providing evidence of differences in membrane permeability. There was a negative correlation between embryo diameter and the total number of larvae (r = -0.372). In conclusion, use of embryonic stages 8.0 and 13.3 haf were recommended for maintaining cooled pacu embryos at -8 °C for 6 or 10 h.

Coral larvae conservation: Physiology and reproduction

Coral species throughout the world's oceans are facing severe environmental pressures. We are interested in conserving coral larvae by means of cryopreservation, but little is known about their cellular physiology or cryobiology. These experiments examined cryoprotectant toxicity, dry weight, water and cryoprotectant permeability using cold and radiolabeled glycerol, spontaneous ice nucleation temperatures, chilling sensitivity, and settlement of coral larvae. Our two test species of coral larvae, Pocillopora damicornis (lace coral), and Fungia scutaria (mushroom coral) demonstrated a wide tolerance to cryoprotectants. Computer-aided morphometry determined that F. scutaria larvae were smaller than P. damicornis larvae. The average dry weight for P. damicornis was 24.5%, while that for F. scutaria was 17%, yielding osmotically inactive volumes (V(b)) of 0.22 and 0.15, respectively. The larvae from both species demonstrated radiolabeled glycerol uptake over time, suggesting they were permeable to the glycerol. Parameter fitting of the F. scutaria larvae data yielded a water permeability 2 microm/min/atm and a cryoprotectant permeability = 2.3 x 10(-4) cm/min while modeling indicated that glycerol reached 90% of final concentration in the larvae within 25 min. The spontaneous ice nucleation temperature for F. scutaria larvae in filtered seawater was -37.8+/-1.4 degrees C. However, when F. scutaria larvae were chilled from room temperature to -11 degrees C at various rates, they exhibited 100% mortality. When instantly cooled from room temperature to test temperatures, they showed damage below 10 degrees C. These data suggest that they are sensitive to both the rate of chilling and the absolute temperature, and indicate that vitrification may be the only means to successfully cryopreserve these organisms. Without prior cryopreservation, both species of coral settled under laboratory conditions.