Aquaculture is the fastest‐growing food‐production sector and is striving to become a long‐term sustainable approach to meet the rising global demand for seafood. During the expansion and advancement of aquaculture, minimizing ecological impacts should occur concomitantly with maximizing production. Farmed fish, often genetically distinct from their natural conspecifics, may pose significant risks of genetic contamination and ecological imbalance to wild populations if they escape from aquaculture confinement. Growing reproductively sterile fish is the most effective way to genetically contain farmed fish. Atlantic salmon (Salmo salar) escape events in the ‘Pacific Northwest’ region of the United States and Canada have raised alarms over potential ecological impacts and led to legislation in Washington State phasing out the culture of non‐native finfish species. Farming sterile native species such as coho salmon (Oncorhynchus kisutch) and sablefish (Anoplopoma fimbria) in the Pacific Northwest would ease public concerns and promote environmentally and economically sustainable aquaculture. Sterile fish also can mitigate the challenge of precocious maturation, a prominent issue associated with culture of salmonids and many other species, to improve somatic growth, flesh quality and fish health and welfare. Here, we review methods having potential applications for producing sterile fish and introduce our novel immersion‐based technology that temporarily silences the dead end (dnd) gene using Morpholino oligonucleotides to produce sterile coho salmon and sablefish for the first time. The successful induction of sterility in these two iconic Pacific Northwest species without introducing genetic modifications would promote the use of this immersion‐based sterilization technology for more aquaculture finfish worldwide.

Germ cell transplantation technology enables surrogate offspring production in fish. This technology has been expected to mitigate reproductive barriers, such as long generation time, limited fecundity, and complex broodstock management, enhancing seed production and productivity in aquaculture. Many studies of germ cell transplantation in various fish species have been reported over a few decades. So far, surrogate offspring production has been achieved in many commercial species. In addition, the knowledge of fish germ cell biology and the related technologies that can enhance transplantation efficiency and productivity has been developed. Nevertheless, the commercial application of this technology still seems to lag behind, indicating that the established models are neither beneficial nor cost-effective enough to attract potential commercial users of this technology. Furthermore, there are existing bottlenecks in practical aspects such as impractical shortening of generation time, shortage of donor cells with limited resources, low efficiency, and unsuccessful surrogate offspring production in some fish species. These obstacles need to be overcome through further technology developments. Thus, we thoroughly reviewed the studies on fish germ cell transplantation reported to date, focusing on the practicality, and proposed potential solutions and future perspectives.

DNA methylation is a key regulator of eukaryotic genomes, most commonly through 5-methylcytosine (5mC). In contrast, the existence and function of N ⁶ -methyladenine (6mA) in eukaryotes have been controversial, with conflicting reports resulting from methodological artifacts. Nevertheless, some unicellular lineages, including ciliates, early-branching fungi and the alga Chlamydomonas , show robust 6mA signals, raising questions about their origin and evolutionary role. Here we apply Oxford Nanopore sequencing to profile 6mA at base-pair resolution across 18 unicellular eukaryotes representing all major supergroups. We find that robust 6mA patterns occur only in species that encode the adenine methyltransferase AMT1. Notably, 6mA consistently accumulates downstream of transcriptional start sites, positioned between H3K4me3-marked nucleosomes, indicating a conserved association with transcriptional activation. Our results support the idea that the last eukaryotic common ancestor had a dual methylation system, with transcription-linked 6mA and repressive 5mC, which has been repeatedly simplified in both multicellular and unicellular lineages through the loss of the AMT1 pathway.

Undesired maturation and reproduction are major challenges in fish aquaculture regarding genetic introgression, precocious maturation, and reproduction-related mortality, which can have profound ecological or economic impacts. Farming reproductively sterile fish can effectively mitigate these challenges. In this paper, we transferred and applied a novel immersion-based, non-transgenic gene silencing technology to sterilize coho salmon for the first time. Unfertilized eggs were bath immersion-treated with csdnd-MO-Vivo in different immersion media. Eyed rates of treated groups ranged from 0.9 to 63.5%. Sterile fish lacking germ cells, and those with arrested germ cells/atretic oocytes, were obtained at 14 and 20 months of age, albeit at a low percentage (2.3 to 10.0% based on females). Gonadal histology and vasa/nanos3 gene expression profile were provided for comparing fertile and sterile gonads, as well as retarded ovaries. Future directions and strategies for optimizing the technology and improving sterility induction were also proposed. The successful production of sterile coho salmon achieved in this study demonstrates the proof of principle for this new sterilization technology. As we continue to expand upon these findings and refine the technology, achieving coho salmon sterile population farming would facilitate the future transfer and application to other commercially important aquaculture fish.

The movement of viruses in aquatic systems is rarely studied over large geographic scales. Oceanic currents, host migration, latitude-based variation in climate, and resulting changes in host life history are all potential drivers of virus connectivity, adaptation, and genetic structure. To expand our understanding of the genetic diversity of Callinectes sapidus reovirus 1 (CsRV1) across a broad spatial and host life history range of its blue crab host (Callinectes sapidus), we obtained 22 complete and 96 partial genomic sequences for CsRV1 strains from the US Atlantic coast, Gulf of Mexico, Caribbean Sea, and the Atlantic coast of South America. Phylogenetic analyses of CsRV1 genomes revealed that virus genotypes were divided into four major genogroups consistent with their host geographic origins. However, some CsRV1 sequences from the US mid-Atlantic shared high genetic similarity with the Gulf of Mexico genotypes, suggesting potential human-mediated movement of CsRV1 between the US mid-Atlantic and Gulf coasts. This study advances our understanding of how climate, coastal geography, host life history, and human activity drive patterns of genetic structure and diversity of viruses in marine animals and contributes to the capacity to infer broadscale host population connectivity in marine ecosystems from virus population genetic data.

Across invertebrates, DNA methylation is largely restricted to the bodies of highly and constitutively expressed genes. This pattern has led to the widespread hypothesis that gene body methylation regulates gene expression and contributes to environmental adaptation and developmental plasticity, often by analogy to its roles in vertebrate genomes. However, mechanistic evidence testing these ideas remains scarce, limiting the interpretation of epigenetic variation in evolutionary and ecological contexts. Here, using the cnidarian model Nematostella vectensis , an early-branching animal which retains an ancestral methylation pattern, we show that loss of DNA methylation produces viable embryos with minimal effects on gene expression. Instead, methylation depletion causes widespread chromatin opening and spurious transcription initiation, particularly from transposable elements embedded within gene bodies. We further demonstrate that methylation is selectively restored in the germline, guided by transcription-associated chromatin, but is not globally reprogrammed after fertilization. As a result, aberrant methylation states can be inherited across generations. These findings identify gene body methylation as an evolutionarily conserved genome defence mechanism, clarify its ancestral function in animal genomes and reveal how incomplete epigenetic resetting can generate heritable regulatory variation with potential evolutionary consequences.