Bluefin tuna sperm production is hastened by surrogacy in small Euthynnus.

Pacific bluefin tuna (Thunnus orientalis) remains heavily depleted due to overexploitation. Aquaculture and stock enhancement based on artificial seedlings could be effective solutions to this problem. However, widespread adoption of seedling production is limited because spawning in captivity of bluefin tuna, a large pelagic top predator, requires much space, time, cost, and labour.

Vitrification of medaka whole testis with a trehalose-containing solution and production of medaka individuals derived from the vitrified cells.

The cryopreservation of teleost eggs and embryos remains challenging, and there are no previous reports that demonstrate successful cryopreservation in medaka (Oryzias latipes). We have reported egg and sperm production, followed by the generation of donor-derived offspring by transplanting vitrified whole testes-derived testicular cells into surrogate fish. The vitrification solutions contained ethylene glycol, sucrose, and ficoll.

Gametes of semelparous salmon are repeatedly produced by surrogate rainbow trout.

Most Pacific salmon species grow in the ocean, return to their native rivers to reproduce, and then die (semelparous type). However, rainbow trout survive after spawning and reproduce repeatedly until the end of their lives (iteroparous type). Little is known about how germline stem cells behave during gametogenesis in the two types of Pacific salmon.

Reproductive Characteristics and Suitability of Sterile dead end Knockout Nibe Croaker as a Recipient for Intraperitoneal Germ Cell Transplantation.

The use of sterile recipients is crucial for efficiently producing donor-derived offspring through surrogate broodstock technology for practical aquaculture applications. Although knockout (KO) of the dead end (dnd) gene has been used in previous studies as a sterilization method, it has not been reported in marine fish. In this study, nibe croaker was utilized as a model for marine teleosts that produce small pelagic eggs, and the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system was utilized to produce dnd KO fish.

Fish germ cell cryobanking and transplanting for conservation.

The unprecedented loss of global biodiversity is linked to multiple anthropogenic stressors. New conservation technologies are urgently needed to mitigate this loss. The rights, knowledge and perspectives of Indigenous peoples in biodiversity conservation-including the development and application of new technologies-are increasingly recognised.

The volume and shape of bitterling eggs are more strongly influenced by germ cell autonomy than by the surrounding somatic cells.

There is great variation in the size and shape of teleost eggs from species to species. The size of the teleost egg depends on the amount of yolk accumulated in the egg, which is an important factor directly affecting the survival of hatchlings. Egg shape also contributes significantly to spawning ecology and survival during the prehatching stage.

Determination of dietary essential fatty acids in a deep-sea fish, the splendid alfonsino Beryx splendens: functional characterization of enzymes involved in long-chain polyunsaturated fatty acid biosynthesis.

The splendid alfonsino Beryx splendens is a commercially important deep-sea fish in East Asian countries. Because the wild stock of this species has been declining, there is an urgent need to develop aquaculture systems. In the present study, we investigated the long-chain polyunsaturated fatty acid (LC-PUFA) requirements of B.

Production of Germ Cell-Less Rainbow Trout by dead end Gene Knockout and their Use as Recipients for Germ Cell Transplantation.

In germ cell transplantation experiments, the use of sterile recipients that do not produce their own gametes is an important prerequisite. Triploidization and dnd gene knockdown (KD) methods have been widely used to produce sterile fish. However, triploidization does not produce complete sterility in some fish species, and gene KD is labor and time intensive since it requires microinjection into individual fertilized eggs.

Characterization of a vasa homolog in Mekong giant catfish (Pangasianodon gigas): Potential use as a germ cell marker.

For the long-term preservation of the genetic resources of endangered fish species, a combination of germ cell cryopreservation and transplantation can be an effective technique. To optimize these techniques, it is important to identify undifferentiated germ cells possessing transplantability, such as primordial germ cells, type A spermatogonia (ASGs), and oogonia. In this study, a homolog of vasa cDNA in Mekong giant catfish (MGC-vasa) (Pangasianodon gigas), which is an endangered species inhabiting the Mekong river, was cloned and characterized for use as a putative germ cell marker.

Allelic diversification after transposable element exaptation promoted as the master sex determining gene of sablefish.

Concepts of evolutionary biology suggest that morphological change may occur by rare punctual but rather large changes, or by more steady and gradual transformations. It can therefore be asked whether genetic changes underlying morphological, physiological, and/or behavioral innovations during evolution occur in a punctual manner, whereby a single mutational event has prominent phenotypic consequences, or if many consecutive alterations in the DNA over longer time periods lead to phenotypic divergence. In the marine teleost, sablefish (), complementary genomic and genetic studies led to the identification of a sex locus on the Y Chromosome.

Identification of the causative gene of a transparent phenotype of juvenile red sea bream Pagrus major.

Deformities in cultured fish species may be genetic, and identifying causative genes is essential to expand production and maintain farmed animal welfare. We previously reported a genetic deformity in juvenile red sea bream, designated a transparent phenotype. To identify its causative gene, we conducted genome-wide linkage analysis and identified two single nucleotide polymorphisms (SNP) located on LG23 directly linked to the transparent phenotype.

Production of functional sperm from cryopreserved testicular germ cells following intraperitoneal transplantation into allogeneic surrogate in yellowtail (Seriola quinqueradiata).

The aim of this study was to establish a method for the cryopreservation of spermatogonia of the yellowtail (Seriola quinqueradiata), which is the most commonly farmed fish in Japan. Testicular cells were prepared by enzymatic dissociation of testicular fragments containing an abundance of type A spermatogonia and were added to cryomedium containing dimethyl sulfoxide (DMSO), ethylene glycol, glycerol, or propylene glycol at concentrations of 0.5-2.

Disrupted eye and head development in rainbow trout with reduced ultraviolet (sws1) opsin expression.

Visual opsins are proteins expressed by retinal photoreceptors that capture light to begin the process of phototransduction. In vertebrates, the two types of photoreceptors (rods and cones) express one or multiple opsins and are distributed in variable patterns across the retina. Some cones form opsin retinal gradients, as in the mouse, whereas others form more demarcated opsin domains, as in the lattice-like mosaic retinas of teleost fishes.

Cryopreservation and Transplantation of Spermatogonial Stem Cells.

Cryopreservation as a method that enables long-term storage of biological material has long been used for the conservation of valuable zebrafish genetic resources. However, currently, only spermatozoa of zebrafish can be successfully cryopreserved, while protocols for cryopreservation of eggs and embryos have not yet been fully developed. Transplantation of germline stem cells (GSCs) has risen as a favorable method that can bypass the current problem in cryopreservation of female genetic resources and can lead to reconstitution of fish species and lines through surrogate production.

Flatfishes colonised freshwater environments by acquisition of various DHA biosynthetic pathways.

The colonisation of freshwater environments by marine fishes has historically been considered a result of adaptation to low osmolality. However, most marine fishes cannot synthesise the physiologically indispensable fatty acid, docosahexaenoic acid (DHA), due to incomplete DHA biosynthetic pathways, which must be adapted to survive in freshwater environments where DHA is poor relative to marine environments. By analysing DHA biosynthetic pathways of one marine and three freshwater-dependent species from the flatfish family Achiridae, we revealed that functions of fatty acid metabolising enzymes have uniquely and independently evolved by multi-functionalisation or neofunctionalisation in each freshwater species, such that every functional combination of the enzymes has converged to generate complete and functional DHA biosynthetic pathways.

Aging- and temperature-related activity of spermatogonial stem cells for germ cell transplantation in medaka.

Spermatogonial transplantation can contribute to developing a novel method of producing seedlings for both aquaculture and biotic conservation. This study's purpose was to investigate aging- and temperature-related changes in the numbers and stem cell functions of type-A spermatogonia (ASG) in the model fish medaka (Oryzias latipes). The ASG numbers in medaka of different ages were quantified via histological observation and enzymatic dissociation of vasa-Gfp medaka testes.

Production of functional eggs and sperm from in vitro-expanded type A spermatogonia in rainbow trout.

Combining cryopreservation of germline stem cells (GSCs) with their subsequent transplantation into recipient fish is a powerful tool for long-term preservation of genetic resources of endangered fishes. However, application of this technique has been limited because endangered species sometimes have small gonads and do not supply enough GSCs to be used for transplantation. This limitation could be overcome by expanding GSCs in vitro, though this has been difficult due to the complexity of reconstructing the gonadal microenvironment that surrounds GSCs.

Suitability of hybrid mackerel (Scomber australasicus × S. japonicus) with germ cell-less sterile gonads as a recipient for transplantation of bluefin tuna germ cells.

We aim to establish a small-bodied surrogate broodstock, such as mackerel, which produces functional bluefin tuna gametes by spermatogonial transplantation. When reproductively fertile fish are used as recipients, endogenous gametogenesis outcompetes donor-derived gametogenesis, and recipient fish predominantly produce their gametes. In this study, we assessed fertility of hybrid mackerel, Scomber australasicus × S.

Production of Chinese rosy bitterling offspring derived from frozen and vitrified whole testis by spermatogonial transplantation.

Bitterling is a small cyprinid fish facing an increasing risk of extinction owing to habitat destruction and decreasing freshwater mussel population that are used as their spawning substrates. Owing to their large size and high yolk contents, methods for cryopreservation of their eggs or embryos, which is a promising method for long-term preservation of their genetic resources, are still not available. We conducted this study to evaluate the feasibility of gamete production by transplanting cryopreserved testicular cells into germ cell-less recipients that were produced by knockdown of dead end gene.

Preservation of zebrafish genetic resources through testis cryopreservation and spermatogonia transplantation.

Zebrafish is one of the most commonly used model organisms in biomedical, developmental and genetic research. The production of several thousands of transgenic lines is leading to difficulties in maintaining valuable genetic resources as cryopreservation protocols for eggs and embryos are not yet developed. In this study, we utilized testis cryopreservation (through both slow-rate freezing and vitrification) and spermatogonia transplantation as effective methods for long-term storage and line reconstitution in zebrafish.

Enrichment of transplantable germ cells in salmonids using a novel monoclonal antibody by magnetic-activated cell sorting.

In the fish germ cell transplantation system, only type A spermatogonia (ASGs) and oogonia are known to be incorporated into the recipient genital ridges, where they undergo gametogenesis. Therefore, high colonization efficiency can be achieved by enriching undifferentiated germ cells out of whole testicular cells. In this study, we used magnetic-activated cell sorting (MACS) for enriching undifferentiated germ cells of rainbow trout using a monoclonal antibody that recognizes a specific antigen located on the germ cell membrane.

A key metabolic gene for recurrent freshwater colonization and radiation in fishes.

Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among lineages are largely unknown.

Establishment of novel monoclonal antibodies for identification of type A spermatogonia in teleosts†.

We recently established a germ cell transplantation system in salmonids. Donor germ cells transplanted into the body cavity of recipient embryos migrate toward and are incorporated into the recipient gonad, where they undergo gametogenesis. Among the various types of testicular germ cells, only type A spermatogonia (A-SG) can be incorporated into the recipient gonads.

Characterization and expression of a vasa homolog in the gonads and primordial germ cells of the striped catfish (Pangasianodon hypophthalmus).

The analysis of early gonadogenesis during larval development requires a molecular marker that is specifically expressed in the germ cell lineage, such as the vasa gene. In this study, we cloned and characterized vasa in the striped catfish (Pangasianodon hypophthalmus), and designated this as Phy-vasa. Phy-vasa contained all of the predicted consensus motifs that are shared among the vasa genes in other fish species, including RG and RGG repeats, ATPase motifs, and a DEAD-box, and phylogenetic analysis using various DEAD-box family proteins demonstrated that the Phy-vasa protein clustered within the Vasa family.

Specific visualization of live type A spermatogonia of Pacific bluefin tuna using fluorescent dye-conjugated antibodies†.

During our previous work toward establishing surrogate broodstock that can produce donor-derived gametes by germ cell transplantation, we found that only type A spermatogonia (ASGs) have the potency to colonize recipient gonads. Therefore, the ability to visualize ASGs specifically would allow the sequential analysis of donor cell behavior in the recipient gonads. Here we produced monoclonal antibodies that could recognize the cell surface antigens of ASGs in Pacific bluefin tuna (Thunnus orientalis), with the aim of visualizing live ASGs.