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Background Tor putitora , the largest freshwater fish of the Indian subcontinent, is an endangered species. Several factors have been attributed towards its continuous population decrease, but very little is known about the gut microbiome of this fish. Also, the fish gut microbiome serves as a reservoir of virulence factors and antibiotic resistance determinants. Therefore, the shotgun metagenomic approach was employed to investigate the taxonomic composition and functional potential of microbial communities present in the gut of Tor putitora , as well as the detection of virulence and antibiotic resistance genes in the microbiome . Results The analysis of bacterial diversity showed that Proteobacteria was predominant phylum, followed by Chloroflexi , Bacteroidetes, and Actinobacteria . Within Proteobacteria , Aeromonas and Caulobacter were chiefly present; also, Klebsiella, Escherichia, and plant symbionts were noticeably detected. Functional characterization of gut microbes endowed the virulence determinants, while surveillance of antibiotic resistance genes showed the dominance of β-lactamase variants. The antibiotic-resistant Klebsiella pneumoniae and Escherichia coli pathovars were also detected. Microbial genome reconstruction and comparative genomics confirmed the presence of Aeromonads , the predominant fish pathogens . Conclusions Gut microbiome of endangered Tor putitora consisted of both commensals and opportunistic pathogens, implying that factors adversely affecting the non-pathogenic population would allow colonization and proliferation of pathogens causing diseased state in asymptomatic Tor putitora. The presence of virulence factors and antibiotic resistance genes suggested the potential risk of dissemination to other bacteria due to horizontal gene transfer, thereby posing a threat to fish and human health. The preservation of healthy gut microflora and limited use of antibiotics are some of the prerequisites for the conservation of this imperilled species.

Tor mahanadicus was originally described as Tor mosal mahanadicus with inadequate information on its morphological traits and no designated type specimen. Currently, T . mahanadicus is synonymized with Tor putitora , solely based on partial molecular data despite significant morphological differences. In this study, we performed an integrated morphological and molecular analysis to redescribe T . mahanadicus from the Mahanadi River. Tor mahanadicus is distinguished from all known Indian Tor species by the presence of 2 complete rows of scales between pelvic fin origin and lateral line, small eye (15.3–16.9% in head length), and a wide mouth gap (21.7–23.8% in head length). Moreover, it undoubtedly distinguished from the closely related species Tor putitora by having a wider body depth (26.8–28.2% in standard length vs. 14.5–19.9%), short snout length (23.3–26.4% in head length vs. 28.0–29.3%) and wide inter orbit space (30.5–37.3% in head length vs. 27.6–28.5%). Additionally, the molecular phylogenetic tree generated from a combination of three genes demonstrates a monophyletic clade separate from the Tor putitora clade. Based on the distinct morphological traits and mitochondrial gene sequences, we established Tor mahanadicus as separate species under the genus Tor .

Increasing temperature due to global warming in the Himalayan regions has severe implications for the survival of aquatic ectotherms. To study the thermal acclimation and heat tolerance of an endangered Himalayan fish species, Tor putitora , we examined tissue-specific mRNA expression patterns of heat-shock proteins ( HSP90β ; HSP70 , HSP60 , HSP47 , HSP30 , and HSP20 ), warm-temperature acclimation proteins ( WAP65-1 ) and cyclin-dependent kinase inhibitor 1B ( CDKN1B ) genes in liver, brain, gill, kidney, muscle, and gonad tissues at the intervals of 10, 20, and 30 days during a high-temperature treatment (34.0 °C) for 30 days. All the tested genes have exhibited tissue-specific and time-dependent expression patterns. Heat shock proteins’ differential expression and modulation across examined tissues indicate their role in long-term cellular adaptation, protection against the cytotoxic effect of hyperthermia, and species acclimation to higher temperatures. WAP65-1 and CDKN1B expression in treatment groups suggests its involvement in maintaining homeostasis, long-term temperature acclimation, and thermotolerance during chronic thermal exposure. The response of studied genes under heat stress indicates their potential use as environmental stress biomarkers in this species. The present study elucidates molecular mechanisms regulating the thermal acclimation capacity and thermotolerance of T. putitora and its survival under future projections of widespread warming in the Himalayan region.

Mahseers, the members of the fish genus Tor, are economically important as sport and food fishes, but their population is declining in South and Southeast Asia. Taxonomic discrepancies exist in discussions surrounding a few species of mahseer in India. In this study, we hypothesize that Tor mosal is wrongly synonymized with T. putitora, and T. barakae with T. tor. To test this, we collected samples from the type localities, and from known distribution areas. We observed a clear morphological distinctiveness among these four species using Principal Component Analysis. The most prominent distinctive parameters among the four species were body depth and head length. Phylogenetic analysis using Bayesian Inference and Maximum Likelihood for both partial mtCOI and mtCytb datasets revealed monophyletic origin, and supported distinctive species level delimitation which was consensus with morphological identity. Moreover, the automatic species delimitation methods (ABGD and PTP) also quantify the four species. The mean K2P distance was 1.57% between T. putitora and T. tor, 2.60% between T. mosal and T. putitora, 3.27% between T. mosal and T. tor, and 2.63% between T. barakae and T. tor. Based on this study, we validate T. mosal and T. barakae, and provide taxonomic keys to the species.

Tor putitora is an endangered cyprinid fish constrained to cold water and is also considered an indicator of a healthy aquatic ecosystem. The present study aimed to examine the haplotypic diversity, genetic variation and population structure of T. putitora isolates using COI and Cyt b gene sequences submitted in GenBank. Bioinformatic analysis was carried out using 106 COI and 183 Cyt b gene sequences as well as 2 reference genome sequences. Analysis of COI and Cyt b gene reveals 18 and 85 haplotypes respectively. Mutation was observed at 44 different sites in COI and 173 in Cyt b gene sequences. Haplotype 4 and haplotype 37 were considered ancestral in COI and Cyt b respectively. Analysis of COI gene reveals moderate haplotype diversity (0.630) and low Nucleotide diversity (0.00662) whereas Cyt b has higher haplotype diversity (0.804) and low Nucleotide diversity (0.00582). Moreover, the neutrality test such as Tajima’s D, and Fu’s Fs showed negative values in both gene sequences, suggesting population expansion attributed to habitat destruction. So, comprehending the genetic variability within and among the T. putitora population is crucial for conserving and managing this species. Integration of genetic diversity into conservation planning can enhance the effectiveness of breeding programs and habitat restoration efforts.

In many aquatic species, alteration of habitats and human-induced barriers shape the population's genetic structure in rivers with longitudinal connectivity. The golden mahseer, Tor putitora (GM) is an endangered and sensitive cyprinid species. It is considered an indicator of a healthy freshwater ecosystem and is found in cold-water habitats. Therefore, it is crucial to understand how longitudinal connectivity and anthropogenic factors affect the diversity and population genetic structure of GM. The population genetic structure, gene flow and demography of the GM in four Himalayan rivers were investigated by mitochondrial cytochrome b gene (cyt b) as well as microsatellite genotyping. The results showed overall high mtDNA diversity (hd: 0.795) couple with low nucleotide diversity ([qi]: 0.0012) in all GM populations. We also found significant levels of observed heterozygosity (ranging from 0.618 to 0.676), with three genetic clusters. The mtDNA and microsatellite analysis suggested that there are close genetic relationships between the Bhagirathi and Ganga populations; whereas, significant level of genetic differentiation was observed with that of Alaknanda and Yamuna populations. Haplotype distribution, unimodal distribution graph and results of the neutrality test indicated a sign of recent population growth in the GM population. Analysis of molecular variance (AMOVA) and spatial molecular variance (SAMOVA) revealed existence of genetic structures in GM populations. In addition, spatial genetic analysis detected a significant correlation between the pairwise genetic and geographical distances for the entire study area (Mantel test, rM = 0.126; P = 0.010). Considering the significant level of heterozygosity, high rate of unidirectional migration and the intra-population structuring in Alaknanda and Yamuna, it is crucial to propose an effective conservation plan for the GM populations. In general, dams obstruct continuous water flow and create isolated microhabitats. Therefore, we recommend the establishment of microscale protected areas near GM breeding sites and construction of fish pass to maintain the genetic connectivity of fish species that enhance viable populations.

The king of rivers or mahseer comprises three genera: Tor, Neolissochilus, and Naziritor, under the Cyprinidae family. The Tor genus has been classified as the true mahseer due to the presence of a median lobe among the three genera. The Tor species are widely distributed across Southeast (SE) Asia, and 13 Tor species have been reported previously: Tor ater, Tor dongnaiensis, Tor douronensis, Tor laterivittatus, Tor mosal, Tor mekongensis, Tor putitora, Tor sinensis, Tor soro, Tor tambra, Tor tambroides, Tor tor and Tor yingjiangensis. However, the exact number of valid Tor species remains debatable. Different and unstandardized approaches of applying genetic markers in taxonomic identification and morphology variation within the same species have further widened the gap and ameliorated the instability of Tor species taxonomy. Therefore, synchronized and strategized research among Tor species researchers is urgently required to improve and fill the knowledge gap. This review is a current update of SE Asia’s Tor species, outlining their distribution, morphology, and genetic identification. In addition, the present review proposes that there are ten valid Tor species in the SE Asian region. This list will serve as a template and standard to improve the taxonomy of the SE Asian Tor species, which could serve as a basis to open new directions in Tor research.

An exopolysaccharide (EPS) synthesizing potentially probiotic Gram-positive bacterial strain was isolated from fish (Tor putitora) gut, and its EPS was structurally characterized. The isolate, designated as FW2, was identified as Lactobacillus reuteri through 16S rRNA gene sequencing and phylogenetic analysis. This isolate produces fructan-type EPS using sucrose as a substrate. Based on 13C-NMR spectroscopy, methylation analysis and monosaccharide composition, the EPS was identified as a linear levan polymer with fructose as main constituent linked via β(2 → 6) linkages. Based on molecular weight (MW) distribution, two groups of levan were found to be produced by the isolate FW2: one with high MW (4.6 × 106 Da) and the other having much lower MW (1.2 × 104 Da). The isolate yielded about 14 g/L levan under optimized culturing parameters including aeration conditions, pH, temperature and substrate concentration. The obtained bimodal molecular weight linear levan is the first of its type to be synthesized by a L. reuteri isolate from fish gut. Bimodal molecular weight prebiotic levan together with the probiotic potential of the producing strain would provide a new promising synbiotic combination for use in aqua culture.

Abstract In South and South East Asia three genera of fish species i.e. Tor, Neolissochilus and Naziritor are commonly known as Mahseer with at least 47 species. Among these 23 belongs to genus Tor, 22 to Neolissochilus and one to Naziritor i.e. Naziritor zhobensis. Recently another species added to genus Naziritor is Naziritor chelynoides in India. Among Tor species Tor putitora (Hamilton) is the most widely distributed Mahseer in Pakistan and other countries of the Indian subcontinent. However, based alone on morphological characters some authors identify the Pakistani counterparts as Tor macrolepis (Heckel), (a species presumed to be found exclusively in the Indus River system) distinct from Tor putitora (a species found in Ganga Brahmaputra River system). In order to resolve this taxonomic ambiguity, present study carried out meristic and morphometric measurements of Mahseer collected from a total of 11 water bodies of Pakistan. Ratios between the morphometric characters were calculated and statistically analyzed using t-test and correlation coefficient. Two species identified as Tor putitora and Naziritor zhobensis were the sole Mahseer inhabitants of Indus system in Pakistan. Tor putitora occurred at all surveyed sites while Nazirtor zhobensis had a distribution range from river Zhob to tributaries of river Gomal the right bank tributaries of River Indus. The study corroborates that there are no unequivocal morphological synapomorphies in any existing populations of both species. The study further demonstrates that head length, a character frequently used in Mahseer taxonomy, is not a good measure for species identification. Finally the present study establishes that Naziritor zhobensis still exists in the water bodies of Pakistan and that golden Mahseer occurring in Indus riverine system of Pakistan is Tor putitora. Resumo No sul e sudeste da Ásia, três gêneros de espécies de peixes, ou seja, Tor, Neolissochilus e Naziritor, são comumente conhecidos como Mahseer com pelo menos 47 espécies. Entre estas, 23 pertencem ao gênero Tor, 22 a Neolissochilus e um a Naziritor, ou seja, Naziritor zhobensis. Recentemente, outra espécie adicionada ao gênero Naziritor é Naziritor chelynoides na Índia. Entre as espécies de Tor, Tor putitora (Hamilton) é o Mahseer mais amplamente distribuído no Paquistão e em outros países do subcontinente indiano. No entanto, com base apenas em caracteres morfológicos, alguns autores identificam as contrapartes paquistanesas como Tor macrolepis (Heckel) (uma espécie que se presume ser encontrada exclusivamente no sistema do rio Indo), distinta de Tor putitora (uma espécie encontrada no sistema do rio Ganga Brahmaputra). A fim de resolver essas ambiguidades taxonômicas, o presente estudo realizou medidas merísticas e morfométricas de Mahseer coletadas em um total de 11 corpos d’água do Paquistão. As razões entre os caracteres morfométricos foram calculadas e analisadas estatisticamente usando o teste t e o coeficiente de correlação. Duas espécies identificadas como Tor putitora e Naziritor zhobensis foram os únicos habitantes Mahseer do sistema fluvial Indo no Paquistão. Tor putitora ocorreu em todos os locais pesquisados, enquanto Nazirtor zhobensis tinha uma faixa de distribuição do rio Zhob aos afluentes do rio Gomal, afluentes da margem direita do rio Indo. O estudo corrobora que não há sinapomorfias morfológicas inequívocas em nenhuma das populações existentes de ambas as espécies. O estudo demonstra ainda que o comprimento da cabeça, um caractere frequentemente usado na taxonomia de Mahseer, não é boa medida para identificação das espécies. Finalmente, o presente estudo estabelece que Naziritor zhobensis ainda existe nos corpos d’água do Paquistão e que o Mahseer dourado ocorrendo no sistema fluvial Indo do Paquistão é Tor putitora.

The endangered golden mahseer (Tor putitora) (Hamilton, 1822) is a famed gamefish that has a restricted area of occupancy in the Himalayas. Owing to overexploitation, hydrologic alteration along rampant riverbed mining in its spawning grounds, both its number and size have significantly declined. A lack of study on the habitat status of the species is hindering the identification of local habitat threats. Planning evidence‐driven conservation demands the identification of critical habitats and local habitat of golden mahseer. Hence, the overall aim of the study was to ascertain the habitat suitability of golden mahseer in its early life stage. For this, Species Distribution Modeling was conducted using spawning and nursing occurrence records. These habitats were mostly restricted to the northern region of its range. Almost 90% of the priority area identified as spawning and nursing habitat by this study is currently unprotected. With the identification of such habitats, conservation intervention can be further planned. The occurrence records of golden mahseer into early life stages: Spawning and nursing and has successfully delineated the current distribution of such habitats across its entire range. Almost 90% of the priority area identified as spawning and nursing habitat by this study is currently unprotected. Our findings stress the importance of community‐based conservation interventions and the necessity to address multiple stressors, including channel modifications and fishing practices.