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

Cryopreservation effect on DNA methylation profile in rainbow trout spermatozoa

Spermatozoa are the cells that are most commonly used for cryopreservation of valuable genetic resources in aquaculture. It is known that fish spermatozoa transmit to the embryo not only their genetic but also their epigenetic profile, especially DNA methylation. Therefore, any alteration of the DNA methylation profile in spermatozoa induces the risk of transmitting epigenetic alterations to the offspring. The aim of this study was to assess the effect of cryopreservation on DNA methylation in rainbow trout spermatozoa. To trigger variable cellular response after freezing-thawing, spermatozoa from mature males were cryopreserved with dimethyl sulfoxide, methanol or glycerol as cryoprotectant. We observed that dimethyl sulfoxide was the best to preserve thawed spermatozoa functions. Methanol only slightly preserved all the cellular parameters, while glycerol failed to protect motility and fertilization ability. The consequences on DNA methylation were assessed using Reduced Representation Bisulfite Sequencing (RRBS). Sperm cryopreservation did not thoroughly impact DNA methylation, although 335-564 differentially methylated cytosines were characterized depending on the cryoprotectant. Very few of them were shared between cryoprotectants, and no correlation with the extent of cellular damage was found. Our study showed that DNA methylation was only slightly altered after sperm cryopreservation, and this may render further analysis of the risk for the progeny very challenging.

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.

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.

Seasonal and age-related changes in semen characteristics and composition of seminal plasma in sex-reverse female rainbow trout (Oncorhynchus mykiss) in comparison with normal males

All-male or all-female progeny is preferable in reproduction of fish species. In rainbow trout, all-female progeny is desirable, and the most common and healthful approach is to use sex reversed (SR) females as broodstock by including androgen hormones through the diet at the larval stage. The purpose of this study was to determine the differences and changes of seminal plasma ions (Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl^-) and pH in 2 to 3 and 3 to 4 year-old SR females, compared with 2 to 3 year-old normal (N) males at the beginning, middle, and end of the spawning season (SS). Additionally, osmolality, spermatozoa concentration, and sperm motility characteristics were determined. Percentages of sperm motility of SR females were negatively correlated with seminal plasma pH and sperm concentrations (r = -0.479 and r = -0.534, respectively, P < 0.05). Seminal plasma pH (7.14 ± 0.05 to 7.40 ± 0.10) in SR females was less than for N males (7.66 ± 0.10 to 8.04 ± 0.10) at all periods of the SS (P < 0.05). The Ca²⁺ concentrations in the mid-SS were 0.74 ± 0.23 mM in N males, 1.09 ± 0.29 mM in 2 to 3 year-old SR females, and 0.83 ± 0.29 in 2 to 3 year-old SR females, without significant differences (P > 0.05). Furthermore, using of 2 to 3 year-old rather than 3 to 4 year-old SR females for reproduction could provide an advantage in terms of sperm motility characteristics. These findings could be useful for not only understanding of SR of semen from sexually reversed females but also for design of a maturation medium both for further studies and aquaculture production.