Effect of postthaw storage time and sperm-to-egg ratio on fertility of cryopreserved brook trout sperm

Development of a Sperm Cryopreservation Protocol for Critically Endangered Mohashol, Tor tor (Hamilton)

This study dealt with the development of a sperm cryopreservation protocol of Tor tor. Sperm was collected from hormone-induced males and the concentration and pH of sperm were estimated as 4.3 ± 0.1 × 10¹⁰ cells/mL and 8.6 ± 0.2, respectively. Activation of sperm motility was evaluated in different osmolalities of NaCl solution where motility of sperm decreased with increasing osmolality of extenders, and was completely inhibited at 319 mOsmol/kg. Similarly, the swimming duration of activated sperm was affected as the osmolality of the extender increased. The duration of initial motility of sperm was recorded as 8.4 ± 0.4 minutes at 48 mOsmol/kg, while the highest motility was recorded as 68.0 ± 7.2 minutes at 128 mOsmol/kg. To evaluate the toxicity of cryoprotectants, sperm was incubated with dimethyl sulfoxide (DMSO) and methanol at 5%, 10%, and 15% concentrations, respectively, for 5-45 minutes. Alsever's solution with 5% and 10% DMSO produced better motility during 5-10 minutes of incubation and 15% DMSO seemed toxic to sperm. For the cryopreservation of sperm, Alsever's solution, egg yolk citrate, and urea egg yolk were used as extenders with DMSO and methanol. Alsever's solution with 10% DMSO provided the highest equilibration (90.0% ± 3.5%) and post-thaw (80.0% ± 3.5%) motility followed by that of 87.0% ± 2.0% and 79.0% ± 1.9% with egg yolk citrate plus DMSO, and 82.0% ± 2.6% and 78.0% ± 2.0% with urea egg yolk plus DMSO, respectively. The sperm cryopreservation protocol developed through this study can be applied for long-term preservation of genetic materials of the critically endangered T. tor, and eventually, it will be an effective tool for protecting them from extinction.

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.

Characteristics and Cryopreservation of Semen of Sex-Reversed Females of Salmonid Fish

Sex reversal has been used as a breeding strategy by salmonid fish to produce genetically and phenotypically single sex populations. Production of all-female fish has great importance for the creation of monosex female triploids of salmonid fish, which are valued for their sterility, lack of female maturation, and larger commercial size. Among salmonids, the majority of rainbow trout (Oncorhynchus mykiss) production is based on all-female production with a high proportion of all-female triploid production in Europe. The main aim of this review is to present the recent knowledge regarding sex-reversed females (SRFs) of salmonid fish. We discuss the methods of sex reversal as well as their effects on the morphology and histology of the reproductive tract. We focus on the characteristics of SRF semen as well as the factors determining semen quality. The lower quality of SRF sperm compared to that of normal males has resulted in the need for the artificial maturation of semen. Most importantly, methods of semen storage-both short-term and long-term (cryopreservation)-that can improve hatchery operations are presented with the special emphasis on recent progress in development of efficient cryopreservation procedures and use of cryopreserved semen in hatchery practice. Moreover, we also address the emerging knowledge concerning the proteomic investigations of salmonid sperm, focusing primarily on the proteomic comparison of normal male and SRF testicular semen and presenting changes in SRF rainbow trout sperm proteome after in vitro incubation in artificial seminal plasma.

Sperm quality in fish: Determinants and affecting factors

Fish sperm quality assessment is helpful for optimizing production and for monitoring the environmental state. Sperm can be monitored relatively easy and, to date, various analyses have been applied and proven to be helpful in this task. Among them, sperm motility parameters such as sperm speed are one of the main performance traits during assisted fish reproduction. Apart from motility the sperm concentration, volume, and seminal plasma pH and osmolality are also frequently evaluated and are the main sperm quality indicators measured in fish sperm. However, other parameters also determine sperm fertilization potential. Recent knowledge reveals several additional parameters of high importance for sperm function. Among them are DNA integration, membrane stability, mitochondria status and enzymatic activity. Measuring all these parameters in fish sperm provides complex knowledge regarding male fertility and helps to improve broodstock maintenance protocols as well as gamete handling and fertilization processes. This review focuses on the presentation of the sperm quality measures for freshwater and marine species of the fish and provides information regarding recent methods of sperm quality evaluation.

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.

Effect of dilution in sperm maturation media and time of storage on sperm motility and fertilizing capacity of cryopreserved semen of sex-reversed female rainbow trout

Masculinized females, also called neomales or sex-reversed females have a male phenotype but retain the female genotype (XX). Therefore, all spermatozoa produced in their functional testes carry an X chromosome, which is desired for the production of all-female rainbow trout populations. Semen of sex-reversed female rainbow trout is of low quality and in vitro maturation is required, which includes dilution of sperm suspensions with specially formulated maturation solutions. The aim of this study was to determine the effect of dilution in different maturation media on sperm quality (sperm motility characteristics and fertilizing capacity) of frozen/thawed sperm of sex-reversed female rainbow trout. The effect of time of post-thaw storage (0, 15, 60 and 120min) on semen quality was also tested. Sperm motility parameters and fertilization rate at the eyed and hatching stages were assessed for post-thaw semen diluted in different media. The cryopreservation procedure resulted in high post-thaw sperm motility of about 57% and did not differ from fresh semen. Unexpectedly, maturation media decreased sperm activation capacity immediately after dilution; however, sperm motility increased over time. Fertilization rates of frozen/thawed semen were high (71-87%) and did not differ significantly between experimental variants at any of tested periods of storage. Our results demonstrated that the effect of the maturation media on frozen/thawed sperm is different from that of fresh sperm. The progressive increase in post-thaw sperm motility in maturation media can potentially be applied to routine hatchery practice.

Progress, challenges and perspectives on fish gamete cryopreservation: A mini-review

Protocols for the cryopreservation of fish gametes have been developed for many different fish species, in special, freshwater salmonids and cyprinids. Methods for sperm freezing have progressed during the last decades due to the increasing number of potential applications: aquaculture (genetic improvement programs, broodstock management, helping with species having reproductive problems), biotechnology studies using model fish species (preservation of transgenic or mutant lines), cryobanking of genetic resources from endangered species, etc. This mini-review tries to give an overview of the present situation of this area of research, identifying the main challenges and perspectives, redirecting the reader to more in-depth reviews and papers.

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.

Potassium ions in extender differentially influence the post-thaw sperm motility of salmonid fish

Potassium ions are known to have an inhibitory effect on the sperm motility of salmonids. For this reason, the addition of K(+) to the extender is frequently applied. However, the effect of the addition of K(+) to the extender has not yet been tested. The aim of this study was to test the influence of potassium ion supplementation of the extender on the sperm motility parameters from five Salmonidae species (rainbow trout (Oncorhynchus mykiss), sex-reversed female rainbow trout, whitefish (Coregonus lavaretus), brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis)). Semen samples were diluted in extender containing 0.18 M glucose in 9% methanol (GM) supplemented with 0, 20 or 40 mM potassium chloride. After thawing sperm were stored for 30, 60, 120 and 240 min at 4 °C. Our results demonstrated that the presence of potassium ions in the extender had a negative effect on percentage of motile sperm in four of the salmonid species. In contrast, potassium ions appeared to have a positive effect on percentage of post-thaw motile sperm in whitefish semen. However, this effect could be mimicked by changing the osmolality of the extender (which was achieved by increasing the glucose concentration to 0.22 M). The addition of potassium ions turned out to have no positive effect on post-thaw storage time. Our results suggest that osmolality, rather than potassium ions, seems to be essential for cryopreservation success of salmonids sperm. Further studies should focus on the effects of small changes in osmolality on the post-thaw quality of semen.

Cryopreservation-induced alterations in protein composition of rainbow trout semen

The aim of this study was to detect cryopreservation-induced alterations in the protein composition of rainbow trout semen using two independent methods 1DE SDS-PAGE prefractionation combined with LC-MS/MS and 2D difference gel electrophoresis followed by MALDI-TOF/TOF identification. Here, we show the first comprehensive dataset of changes in rainbow trout semen proteome after cryopreservation, with a total of 73 identified proteins released from sperm to extracellular fluid, including mitochondrial, cytoskeletal, nuclear, and cytosolic proteins. Our study provides new information about proteins released from sperm, their relation to sperm structure and function, and changes of metabolism of sperm cells as a result of cryopreservation. The identified proteins represent potential markers of cryoinjures of sperm structures and markers of the disturbances of particular sperm metabolic pathways. Further studies will allow to decipher the precise function of the proteins altered during rainbow trout cryopreservation and are useful for the development of extensive diagnostic tests of sperm cryoinjures and for the successful improvement of sperm cryopreservation of this economically important species.

New extender for cryopreservation of Siberian sturgeon (Acipenser baerii) semen

The goal of this study was to develop a simple glucose-methanol extender for cryopreservation of Siberian sturgeon (Acipenser baerii) semen. Semen quality was assessed by determining post-thaw sperm motility and fertilizing ability at hatching stage. We tested the effect of glucose concentration (0, 0.10, 0.15, 0.20 and 0.30 M) in a methanol extender on post-thaw sperm motility. Sperm motility parameters and fertilizing ability of semen cryopreserved in 0.1 M glucose in 15% methanol (GM) were compared to previously described Tris-sucrose-KCl in 10% - methanol extender (TSKM). Additionally, sperm motility and fertilizing ability in relation to 30 min equilibration in GM extender before cryopreservation and 30 min of post-thaw storage were determined. The beneficial effect of the glucose for semen cryopreservation was related to its concentration with a quite narrow optimum of 0.1 to -0.15 M. The fertilization rates of frozen/thawed sperm were similar for both (TSKM and GM) tested extenders. The sperm motility and fertilization rate were not affected either by 30 min equilibration in GM extender or by 30 min of post-thaw storage. Our work indicates that the use a simple extender consisting of 0.1M glucose in 15% methanol can be an alternative cryopreservation method to those previously described for sturgeons. The use of an equilibration period and the possibility of post-thaw semen storage can improve organization of hatchery work and help with logistics of large-scale hatchery operations.