The barramundi (Lates calcarifer), a significant aquaculture species, typically displays silver to bronze coloration. However, attention is now drawn to rare variants like the \"panda\" phenotype, characterized by blotch-like patterns of black (PB) and golden (PG) patches. This phenotype presents an opportunity to explore the molecular mechanisms underlying color variations in teleosts. Unlike stable color patterns in many fish, the \"panda\" variant demonstrates phenotypic plasticity, responding dynamically to unknown cues. We propose a complex interplay of genetic factors and epigenetic modifications, focusing on DNA methylation. Through a multiomics approach, we analyze transcriptomic and methylation patterns between PB and PG patches. Our study reveals differential gene expression related to melanosome trafficking and chromatophore differentiation. Although the specific gene responsible for the PB-PG difference remains elusive, candidate genes like asip1, asip2, mlph, and mreg have been identified. Methylation emerges as a potential contributor to the \"panda\" phenotype, with changes in gene promoters like hand2 and dynamin possibly influencing coloration. This research lays the groundwork for further exploration into rare barramundi color patterns, enhancing our understanding of color diversity in teleosts. Additionally, it underscores the \"panda\" phenotype\'s potential as a model for studying adult skin coloration.

The red spotted grouper Epinephelus akaara is a marine species of economic importance and also at risk of extinction. This study investigated the effects of high water temperature on the growth and maturation of juvenile E. akaara females. From 160-420 days post-hatching (dph), the fish were maintained under natural water temperature (NT) and a constant high-water temperature (HT). From 240 dph, both the total length and body weight in the HT group were greater than in NT group. After 360 dph, the gonadosomatic index was also increased in the HT group compared to NT group. Mature oocytes were only observed in the HT group at 330, 360, and 390 dph. Both kiss1 and kiss2 levels increased at 240 and 270 dph in both groups; however, they were greater in the HT group at 240 dph. Similarly, gpr54 levels after 360 dph were greater in the HT group, suggesting that kisspeptin is related to maturation via its receptor gpr54. Levels of fshβ and lhβ were greater in the HT group after 360 dph. Estradiol-17β (E2) levels after 160 dph (except 300 dph) were greater in the HT group than in the NT group, suggesting that the higher E2 levels trigger maturation, and is related to increased fshβ and lhβ. This study provides evidence that high water temperature is effective in accelerating growth and triggering early maturation of juvenile E. akaara, via regulating gpr54, fshβ, lhβ, and E2 levels.

Early embryonic development is crucially important but also remarkably diverse among animal taxa. Axis formation and cell lineage specification occur due to both spatial and temporal control of gene expression. This complex system involves various signaling pathways and developmental genes such as transcription factors as well as other molecular interactants that maintain cellular states, including several types of epigenetic marks. 5mC DNA methylation, the chemical modification of cytosines in eukaryotes, represents one such mark. By influencing the compaction of chromatin (a high-order DNA structure), DNA methylation can either repress or induce transcriptional activity. Mammals exhibit a reprogramming of DNA methylation from the parental genomes in the zygote following fertilization, and later in primordial germ cells (PGCs). Whether these periods of methylation reprogramming are evolutionarily conserved, or an innovation in mammals, is an emerging question. Looking into these processes in other vertebrate lineages is thus important, and teleost fish, with their extensive species richness, phenotypic diversity, and multiple rounds of whole genome duplication, provide the perfect research playground for answering such a question. This review aims to present a concise state of the art of DNA methylation reprogramming in early development in fish by summarizing findings from different research groups investigating methylation reprogramming patterns in teleosts, while keeping in mind the ramifications of the methodology used, then comparing those patterns to reprogramming patterns in mammals.

Teleost fish exhibit the most pronounced and widespread adult neurogenesis. Recently, functional development and the fate of newborn neurons have been reported in the optic tectum (OT) of fish. To determine the role of neurogenesis in the OT, this study used histological, immunohistochemical, and electron microscopic investigations on 18 adult Molly fish specimens (Poecilia sphenops). The OT of the Molly fish was a bilateral lobed structure located in the dorsal part of the mesencephalon. It exhibited a laminated structure made up of alternating fiber and cellular layers, which were organized into six main layers. The stratum opticum (SO) was supplied by optic nerve fibers, in which the neuropil was the main component. Radial bipolar neurons that possessed bundles of microtubules were observed in the stratum fibrosum et griseum superficiale (SFGS). Furthermore, oligodendrocytes with their processes wrapped around the nerve fibers could be observed. The stratum album centrale (SAC) consisted mainly of the axons of the stratum griseum centrale (SGC) and the large tectal, pyriform, and horizontal neurons. The neuronal cells of the SO and large tectal cells of the SAC expressed autophagy-related protein-5 (APG5). Interleukin-1β (IL-1β) was expressed in both neurons and glia cells of SGC. Additionally, inducible nitric oxide synthase (iNOS) was expressed in the neuropil of the SAC synaptic layer and granule cells of the stratum periventriculare (SPV). Also, transforming growth factor beta (TGF-β), SRY-box transcription factor 9 (SOX9), and myostatin were clearly expressed in the proliferative neurons. In all strata, S100 protein and Oligodendrocyte Lineage Transcription Factor 2 (Olig2) were expressed by microglia, oligodendrocytes, and astrocytes. In conclusion, it was possible to identify different varieties of neurons in the optic tectum, each with a distinct role. The existence of astrocytes, proliferative neurons, and stem cells highlights the regenerative capacity of OT. RESEARCH HIGHLIGHTS: The OT of the Molly fish exhibited a laminated structure made up of alternating fiber and cellular layers, which were organized into six main layers. Radial bipolar neurons that possessed bundles of microtubules were observed in the stratum fibrosum et griseum superficiale (SFGS). The stratum album central (SAC) consisted mainly of the axons of the stratum griseum centrale (SGC) and the large tectal, pyriform, and horizontal neurons. Inducible nitric oxide synthase (iNOS) was expressed in the neuropil of the SAC synaptic layer and granule cells of the stratum periventricular (SPV). Also, transforming growth factor beta (TGF-β), SRY-box transcription factor 9 (SOX9), and myostatin were clearly expressed in the proliferative neurons. The existence of astrocytes, proliferative neurons, and stem cells highlights the regenerative capacity of OT.

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This comprehensive review examines the role of fish thrombocytes, cells considered functionally analogous to platelets in terms of coagulation, but which differ in their origin and morphology. Despite the evolutionary distance between teleosts and mammals, genomic studies reveal conserved patterns in blood coagulation, although there are exceptions such as the absence of factors belonging to the contact system. Beyond coagulation, fish thrombocytes have important immunological functions. These cells express both proinflammatory genes and genes involved in antigen presentation, suggesting a role in both innate and adaptive immune responses. Moreover, having demonstrated their phagocytic abilities, crucial in the fight against pathogenic microorganisms, underscores their multifaceted involvement in immunity. Finally, the need for further research on the functions of these cells is highlighted, in order to better understand their involvement in maintaining the health of aquaculture fish. The use of standardized and automated methods for the analysis of these activities is advocated, emphaiszing their potential to facilitate the early detection of stress or infection, thus minimizing the economic losses that these adverse situations can generate in the field of aquaculture.

Turquoise killifish (Nothobranchius furzeri) evolved a naturally short lifespan of about six months and exhibit aging hallmarks that affect multiple organs. These hallmarks include protein aggregation, telomere shortening, cellular senescence, and systemic inflammation. Turquoise killifish possess the full spectrum of vertebrate-specific innate and adaptive immune system. However, during their recent evolutionary history, they lost subsets of mucosal-specific antibody isoforms that are present in other teleosts. As they age, the immune system of turquoise killifish undergoes dramatic cellular and systemic changes. These changes involve increased inflammation, reduced antibody diversity, an increased prevalence of pathogenic microbes in the intestine, and extensive DNA damage in immune progenitor cell clusters. Collectively, the wide array of age-related changes occurring in turquoise killifish suggest that, despite an evolutionary separation spanning hundreds of millions of years, teleosts and mammals share common features of immune system aging. Hence, the spontaneous aging observed in the killifish immune system offers an excellent opportunity for discovering fundamental and conserved aspects associated with immune system aging across vertebrates. Additionally, the species\' naturally short lifespan of only a few months, along with its experimental accessibility, offers a robust platform for testing interventions to improve age-related dysfunctions in the whole organism and potentially inform the development of immune-based therapies for human aging-related diseases.

The telencephalon of ray-finned fishes undergoes eversion, which is very different to the evagination that occurs in most other vertebrates. Ventricle morphogenesis is key to build an everted telencephalon. Thus, here we use the apical marker zona occludens 1 to understand ventricle morphology, extension of the tela choroidea and the eversion process during early telencephalon development of four teleost species: giant danio (Devario aequipinnatus), blind cavefish (Astyanax mexicanus), medaka (Oryzias latipes), and paradise fish (Macroposus opercularis). In addition, by using immunohistochemistry against tubulin and calcium-binding proteins, we analyze the general morphology of the telencephalon, showing changes in the location and extension of the olfactory bulb and other telencephalic regions from 2 to 5 days of development. We also analyze the impact of abnormal eye and telencephalon morphogenesis on eversion, showing that cyclops mutants do undergo eversion despite very dramatic abnormal eye morphology. We discuss how the formation of the telencephalic ventricle in teleost fish, with its characteristic shape, is a crucial event during eversion.

Based on long-term and often frustrating experiences with the poor quality of tapeworms (Cestoda) collected throughout the world for taxonomic and phylogenetic studies, and considering the increasing obstacles to obtaining new material, a simple, easy-to-use and illustrated methodological guide (manual) is provided. It focusses mainly on key steps in examining hosts, collecting cestodes from poikilothermous vertebrates except elasmobranchs, i.e., from ray-finned fish (Actinopterygii), amphibians and \'reptiles\' (a paraphyletic group comprising all sauropsids except birds), and fixing them for subsequent morphological and molecular study. It is proposed that the following methodological points should be followed: (i) ideally only freshly euthanised hosts (not previously frozen) should be used for parasitological examination; (ii) hosts examined should be documented by photographs; host tissue should also be preserved for future genotyping if necessary; (iii) tapeworms should be detached carefully to keep the scolex intact and properly cleaned before fixation; (iv) a small piece of cestode tissue should be always preserved in molecular grade ethanol for DNA sequencing; (v) tapeworms should be fixed as quickly as possible after collecting them and while they are still alive, always using hot (heated) fixatives; this prevents unnatural contraction or deformation and ensures uniform fixation; (vi) each sample (vial) should be properly labelled (a unique code should be given to every cestode sample); (vii) vouchers of sequenced specimens (hologenophores or paragenophores) should always be preserved for identification, and deposited in internationally recognised collections. It is hoped that this guide helps researchers and students to properly process valuable material of cestodes to make it suitable for reliable identification including genotyping and comparative anatomy, which is a prerequisite for any subsequent ecological, biogeographical, phylogenetic life cycle or molecular study.

A macrourid, Coryphaenoides yaquinae sp. inc., was observed to be attracted to bait and exhibiting normal foraging behaviour during a period of 80 min within view of a baited video camera on the sea floor at 7259 m - the deepest ever observation of a fish species with a swim bladder. The buoyancy provided by an oxygen-filled swim bladder at 74.4 MPa pressure was estimated to be 0.164 N, at a theoretical energy cost of 20 kJ, 200 times less than the cost of equivalent lipid buoyancy. During normal metabolism, 192 days would be required to fill the swimbladder. At these depths, oxygen is very incompressible, so changes in volume during ascent or descent are small. However, swimbladder function is crucially dependent on a very low rate of diffusion of oxygen across the swimbladder wall. The oxygen in the swimbladder could theoretically sustain aerobic metabolism for over 1 year but is unlikely to be used as a reserve.