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In this study, we aimed to clarify the taxonomic status of Belonidae species distributed in the Mediterranean Sea and the Black Sea by conducting detailed genetic and morphological markers. A total of 550 needlefish samples were caught between January 2022 and January 2024. The data set used in the study contains a total of 171 sequences for the COI gene and 120 sequences for the 12s rRNA gene from different Belonidae species, including data from GenBank. Systematic analysis of needlefish species was investigated by using sequencing of mtDNA COI and 12s rRNA gene regions and morphological characters in the Turkish Marine Waters. A separate analysis of the two mitochondrial genes supported by morphological characters revealed that each species is grouped within itself. The genetic and morphological analyses showed that Belone belone acus and Belone belone euxini which are considered as the subspecies of Belone belone are not subspecies of the genus Belone and should be considered at the species level, Belone belone . Belone svetovidovi is also considerably different from Belone belone and should be considered as a different species. T. acus imperialis , which is thought to be distributed in the Mediterranean Sea, is not a subspecies of Tylosorus acus and should be revised as Tylosorus imperialis which genetically differs from Tylosorus acus and also other Tylosorus species at the species level.

Isopods infest fish worldwide, but their role as disease vectors remains poorly understood. Here, we describe infestation of Atlantic bonefish ( Albula vulpes ) in Belize with isopods in two of three locations studied, with infestation rates of 15 and 44%. Isopods fed aggressively, and infested fish showed missing scales and scars. Gross morphologic and molecular phylogenetic analyses revealed the isopods to cluster within the family Aegidae and to be most closely related to members of the genus Rocinela , which are globally distributed micro-predators of fish. Metagenomic analysis of 10 isopods identified 11 viruses, including two novel reoviruses ( Reovirales ) in the families Sedoreoviridae and Spinareoviridae . The novel sedoreovirus clustered phylogenetically within an invertebrate-specific clade of viruses related to the genus Orbivirus , which contains arboviruses of global concern for mammal health. The novel spinareovirus clustered within the fish-infecting genus Aquareovirus , which contains viruses of global concern for fish health. Metagenomic analyses revealed no evidence of infection of bonefish with the novel aquareovirus, suggesting that viremia in bonefish is absent, low, or transient, or that isopods may have acquired the virus from other fish. During field collections, isopods aggressively bit humans, and blood meal analysis confirmed that isopods had fed on bonefish, other fish, and humans. Vector-borne transmission may be an underappreciated mechanism for aquareovirus transmission and for virus host switching between fish and other species, which has been inferred across viral families from studies of deep virus evolution.

Understanding factors driving diversity across biodiversity hotspots is critical for formulating conservation priorities in the face of ongoing and escalating environmental deterioration. While biodiversity hotspots encompass a small fraction of Earth's land surface, more than half the world's plants and two-thirds of terrestrial vertebrate species are endemic to these hotspots. Tropical Southeast (SE) Asia displays extraordinary species richness, encompassing four biodiversity hotspots, though disentangling multiple potential drivers of species richness is confounded by the region's dynamic geological and climatic history. Here, we use multilocus molecular genetic data from dense multispecies sampling of freshwater fishes across three biodiversity hotspots, to test the effect of Quaternary climate change and resulting drainage rearrangements on aquatic faunal diversification. While Cenozoic geological processes have clearly shaped evolutionary history in SE Asian halfbeak fishes, we show that paleo-drainage re-arrangements resulting from Quaternary climate change played a significant role in the spatiotemporal evolution of lowland aquatic taxa, and provide priorities for conservation efforts.

A new genus and species of monogenean belonging to Axinidae, Ondoella sajori n. g., n. sp. , is described based on specimens collected from the gill of Japanese halfbeak, Hyporhamphus sajori (Temminck & Schlegel) (Beloniformes: Hemiramphidae) from the Seto Inland Sea, Japan. Ondoella n. g. differs from all other genera of axinids mainly by the possession of an unarmed cirrus. Ondoella n. g. is characterised by the following features: (i) the spherical cirrus present; (ii) spines on the cirrus absent; (iii) the genital pore with a crown of a row of spines; (iv) the elongate body; (v) the vaginal pore with a horn-like spine, and (vi) vaginal pore dorsolateral. The phylogenetic analysis based on 28S rDNA sequences suggests that O. sajori and Axinidae constitute a monophyletic group. A comprehensive list of parasites known to infect H . sajori provided.

The garfish Belone belone represents the only valid endemic Belone species for the Mediterranean Sea and the eastern Atlantic Ocean. It shows a wide global distribution range, with a high commercial value and ecological relevance in the pelagic domain. Despite this, there needs to be more knowledge regarding the otoliths of this species, with the total absence of descriptions regarding asterisci and lapilli from Mediterranean populations and a lack of studies on the reliability of shape analysis on its sagittae. The present paper aims to provide the first main contours description of the three otoliths pairs from a Mediterranean population, providing an accurate investigation of morphology, morphometry, and intra-specific variability of sagittae, lapilli, and asterisci. Results showed (i) the absence of directional bilateral asymmetry and sexual asymmetry for the three otoliths pairs, (ii) a different morphology and morphometry of sagittae, lapilli and asterisci than those described in the literature, and (iii) an enhanced variability between sagittae morphometry and shape between the three investigated size classes. All these data confirmed the reliability of the studied species of shape analysis, showing a geographical and size-related variability of otoliths features probably related to genetics, environmental conditions, and life habits variations.

The Pacific saury ( Cololabis saira ) is one of the most commercially important pelagic fishes in Asia–Pacific countries. The oceanographic environment, especially the Oyashio Current, significantly affects the distribution of Pacific saury, and may lead to variations in their migration route and the formation of fishing grounds in Japanese coastal region and the high seas. In this study, six oceanographic factors, sea surface temperature (SST), sea surface chlorophyll- a concentration (SSC), sea surface salinity (SSS), sea surface height (SSH), mixed layer depth (MLD), and eddy kinetic energy (EKE), were associated with the monthly catch per unit effort 1 (monthly CPUE 1 , ton/vessel) and the monthly CPUE 2 (ton/day) of Pacific saury from Chinese fishing vessels during the optimal fishing periods (September–November) in 2014–2017. The gradient forest analysis showed that the performance of monthly CPUE 1 was higher than monthly CPUE 2 and SST was the most important oceanographic factor influencing monthly CPUE 1 , followed by EKE. The generalized additive model indicated that SST, SSH, and EKE negatively affected monthly CPUE 1 , whereas SSC, SSS, and MLD induced dome-shaped increases in monthly CPUE 1 . The distributions of fishing locations are likely to form along Offshore Oyashio current and meanders, especially in October and November. Synchronous trends in the relationship between the intrusion area of the Oyashio and relative abundance variation index suggest that an increase in the intrusion area of the Oyashio causes more Pacific saury to migrate to the Japanese coastal region, and vice versa. These findings extend our understanding of the effects of the oceanographic environment on Pacific saury.

Geographical distribution plays a major role in our understanding of marine biodiversity. Some marine fish trematodes have been shown to have highly restricted geographical distributions, while some are known to occur over very wide ranges; however, very few of these wide distributions have been demonstrated genetically. Here, we analyse species of the genus Schikhobalotrema (Haplosplanchnidae) parasitizing beloniforms from the tropical west Pacific, the eastern Pacific and the Gulf of Mexico (GoM). We test the boundaries of these trematodes by integrating molecular and morphological data, host association, habitat of the hosts and geographical distribution, following a recently proposed and standardized delineation method for the recognition of marine trematode species. Based on the new collections, Schikhobalotrema huffmani is here synonymized with the type-species of the genus, Schikhobalotrema acutum; Sch. acutum is now considered to be widely distributed, from the GoM to the western Pacific. Additionally, we describe a new species, Schikhobalotrema minutum n. sp., from Strongylura notata and Strongylura marina (Belonidae) from La Carbonera coastal lagoon, northern Yucatán, GoM. We briefly discuss the role of host association and historical biogeography of the hosts as drivers of species diversification of Schikhobalotrema infecting beloniforms.

Flying fishes (Exocoetidae) are a highly specialized group of Beloniformes, with 4 subfamilies, 7 genera, and 78 species. However,only a small number of species of flying fishes have the mitochondrial genome described sof ar. Considering the importance of mitogenomes in evolution, in this study we aimed to expand the description of mitochondrial genomes and the phylogenetic relationships of Exocoetidae. We used publicly available DNA-Seq libraries to assemble the mitochondrial genomes of 7 species of flying fishes. The mitochondrial genomes of Exocoetidae showed conserved features among all species. With 22 tRNAs, 2 rRNAs, and 13 protein-coding genes, they share common features among vertebrates. was reconstructedaspolyphyletic, with four clades, which reinforces previous studies that recovered as non-monophyletic.Werecoveredallfour subfamilies as monophyletic,with Parexocoetinae as the sister group of all other subfamilies.The genetic distance between Exocoetidae species was two times smaller than the genetic distance among the species, indicating a low genetic divergence in the family. Hereby, this study expanded the knowledge of mitochondrial genome features and presented one of the most comprehensive mitochondrial genome datasets used for studying flying fishestodate. This was achievable using publicly available data, reinforcing the importanceof the re-use of such data in the fields of mitogenomics and phylogenetics.

Background The caudal fin of teleosts is a highly diverse morphological structure and a valuable source of information for comparative analyses. Within the Atherinomorpha a high variation of conditions of the caudal-fin skeleton can be found. These range from complex but basal configurations to simple yet derived configurations. When comparing atherinomorph taxa, it is often difficult to decide on the homology of skeletal elements if only considering adult specimens. However, observing the development of caudal-fin skeletons allows one to evaluate complex structures, reveal homologies and developmental patterns, and even reconstruct the grundplan of the examined taxa. Results We studied the development of the caudal-fin skeleton in different atheriniform, beloniform and cyprinodontiform species using cleared and stained specimens. Subsequently we compared the development to find similarities and differences in terms of 1) which structures are formed and 2) which structures fuse during ontogeny. For many structures, i.e., the parhypural, the epural(s), the haemal and neural spines of the preural centra and the uroneural, there were either no or only minor differences visible between the three taxa. However, the development of the hypurals revealed a high variation of fusions within different taxa that partly occurred independently in atheriniforms, beloniforms and cyprinodontiforms. Moreover, comparing the development of the ural centra exposed two ways of formation of the compound centrum: 1) in atheriniforms and the beloniforms Oryzias and Hyporhamphus limbatus two ural centra develop and fuse during ontogeny while 2) in cyprinodontiforms and Exocoetidae (Beloniformes) only a single ural centrum is formed during ontogeny. Conclusions We were able to reconstruct the grundplan of the developmental pattern of the caudal-fin skeleton of the Atheriniformes, Beloniformes and Cyprinodontiformes as well as their last common ancestors. We found two developmental modes of the compound centrum within the Atherinomorpha, i.e., the fusion of two developing ural centra in atheriniforms and beloniforms and the development of only one ural centrum in cyprinodontiforms. Further differences and similarities for the examined taxa are discussed, resulting in the hypothesis that the caudal-fin development of a last common ancestor to all atherinomorphs is very much similar to that of extant atheriniforms.