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Holocephali is a subclass of chondrichthyans with ample geographic distribution in marine ecosystems. Holocephalan species are organized into three families: Callorhinchidae, Chimaeridae, and Rhinochimaeridae. Despite the critical ecological and evolutionary importance, genomic information from holocephalans is still scarce, particularly from rhinochimaerids. The present study provides the first complete mitogenome of the Atlantic longnose chimaera Rhinochimaera atlantica (Holt & Byrne, 1909). The whole mitogenome was sequenced from an R. atlantica specimen, collected on the Porcupine Bank (NE Atlantic), by Illumina high-throughput sequencing. The R. atlantica mitogenome has 17,852 nucleotides with 13 protein-coding genes, 22 transfer RNA, and two ribosomal RNA genes. Nine of these genes are in the complementary strand. This mitogenome has a GC content of 41.5% and an AT content of 58.5%. The phylogenetic reconstruction provided here, using all the available complete and partial Holocephali mitogenomes, places R. atlantica in the Rhinochimaeridae family, as expected. This genomic resource will be useful in the genomic characterization of this species. [ABSTRACT FROM AUTHOR]

Chondrichthyans (sharks, rays and chimeras) are a fascinating and highly vulnerable group of early branching gnathostomes. However, they remain comparatively poorly sampled from the point of view of molecular resources, with deep water taxa being particularly data deficient. The development of long-read sequencing technologies enables the analysis of phylogenetic relationships through a precise and reliable assembly of complete mtDNA genomes. The sequencing and characterization of the complete mitogenome of the opal chimera Chimera opalescens Luchetti, Iglésias et Sellos 2011, using the long-read technique PacBio HiFi is presented. The entire mitogenome was 23,411 bp long and shows the same overall content, i.e. 13 protein-coding genes, 22 transfer RNA and 2 ribosomal RNA genes, as all other examined Chondrichthyan mitogenomes. Phylogenetic reconstructions using all available Chondrichthyan mitogenomes, including 11 Holocephali (chimeras and ratfishes), places C. opalescens within the Chimaeridae family. Furthermore, the results reinforce previous findings, showing the genus Chimera as paraphyletic and thus highlighting the need to expand molecular approaches in this group of cartilaginous fishes. [ABSTRACT FROM AUTHOR]

Marine annelids are a globally distributed and species-rich group, performing important ecological roles in macrobenthic communities. Yet, the availability of molecular resources to study these organisms is scarcer, comparatively with other phyla. Here, we present the first complete mitogenome of the Atlantic ragworm Hediste diversicolor (OF Muller, 1776). The mitogenome (15,904 bp long) contains 13 protein-coding genes, 22 transfer RNA, and two ribosomal RNA genes, all encoded in the same strand. Gene arrangement and composition are identical to those observed in two available congeneric species, Hediste diadroma and Hediste japonica. The phylogenetic analysis using both maximum-likelihood and Bayesian inference methods reveal a well-supported monophyly of genus Hediste and the already reported paraphyletic relationships within the subfamilies Nereidinae and Gymnonereidinae. Our results highlight the relevance of increasing the molecular sampling within this diverse group of marine fauna. [ABSTRACT FROM AUTHOR]

Cartilaginous fish are fascinating taxa, present in the folklore and art of many different cultures. Moreover, they display several unique anatomical, physiological, molecular, and behavioral characteristics making them extremely interesting from a biological perspective. Nevertheless, some crucial knowledge gaps remain, including phylogenetic relationships among extant species. Here, we produced the complete mitogenome sequence of the large-eyed rabbitfish, Hydrolagus mirabilis (Chimaeriformes). The complete mitogenome is 19,435 bp long and shows the same overall content, i.e. 13 protein-coding genes, 22 transfer RNA, and two ribosomal RNA genes, as all other examined Chondrichthyan mitogenomes. Phylogenetic reconstructions including 12 Holocephalan and three outgroup Elasmobranch mitogenomes place the H. mirabilis within the family Chimaeridae but revealed paraphyletic Hydrolagus and Chimaera, in line with a previous study, highlighting the importance for collecting additional molecular data to improve phylogenetic reconstruction in this group of vertebrates. [ABSTRACT FROM AUTHOR]

Haemulidae is a widely diverse and widespread family of New World teleost fish. The Peruvian grunt, Anisotremus scapular, inhabits the South American Pacific coast where its overexploitation for human consumption. Fishing has led to the populational decline of the species and raised the need for conservation and aquaculture developments. Here we describe the complete mitogenome of the Peruvian grunt assembled from an RNA-seq dataset. The mitogenome length is 16,785 bp and, as expected for a vertebrate, composed of 13 PCGs, 22 transfer RNA, 2 ribosomal RNA genes. Phylogenetic reconstruction, including all available 25 Lutjaniformes mitogenomes, places A. scapularis within the family Haemulidae, more precisely within the subfamily Haemulinae. Furthermore, paraphyletic relationships were observed within the other groups represented in the phylogeny. Overall, our results highlight the usefulness of using mitochondrial genomes for phylogenetic analysis in Haemulinae as well as the necessity to increase taxonomic sampling within the group. [ABSTRACT FROM AUTHOR]

Cartilaginous fishes are a highly vulnerable vertebrate group but remain poorly studied, especially those occupying deep-water ecological niches. Here, we describe the complete mitogenome of the deep-water chimaeriform Hydrolagus affinis (de Brito Capello, 1868) (Holocephali: Chimaeridae). The mitogenome has 19,437 nucleotides and the same overall content, i.e. 13 protein-coding genes, 22 transfer RNA, 2 ribosomal RNA genes, as available for all cartilaginous fishes mitogenomes. Phylogenetic reconstructions including 615 cartilaginous fishes mitogenomes place the H. affinis within the family Chimaeridae but suggest that Hydrolagus and Chimera are not reciprocally monophyletic, highlighting the need for additional molecular data to improve phylogenetic reconstruction. [ABSTRACT FROM AUTHOR]

Both field and experimental data examined the influence of exposure to environmental contaminant tributyltin (TBT) on marine organisms. Although most attention focused on the imposex phenomenon in gastropods, adverse effects were also observed in other taxonomic groups. It has been shown that imposex induction involves modulation of retinoid signaling in gastropods. Whether TBT influences similar pathways in fish is yet to be addressed. In this study, larvae of the model teleostDanio reriowere exposed to natural retinoids, all-trans-retinoic acid, 9-cis-retinoic acid, and all-trans-retinol, as well as to the RXR synthetic pan-agonist methoprene acid (MA) and to TBT. Larvae were exposed to TBT from 5 days post fertilization (dpf) to adulthood, and reproductive capacity was assessed and correlated with mode of action. TBT significantly decreased fecundity at environmentally relevant levels at 1 μg TBT Sn/g in diet. Interestingly, in contrast to previous reports, TBT altered zebrafish sex ratio toward females, whereas MA exposure biased sex toward males. Since fecundity was significantly altered in the TBT-exposed group with up to 62% decrease, the potentially affected pathways were investigated. Significant downregulation was observed in brain mRNA levels of aromatase b (CYP19a1b) in females and peroxisome proliferator activated receptor gamma (PPARg) in both males and females, suggesting an involvement of these pathways in reproductive impairment associated with TBT. [ABSTRACT FROM PUBLISHER]

The difficulties involved in the study of deep-sea species imply the existence of a wide gap in knowledge of this ecosystem. Here, we have obtained the mitogenome of the Oven's halosaur, Halosaurus ovenii, for the first time using low coverage Illumina Paired-end (PE) sequencing. This species belongs to order Notacanthiformes, a poorly studied group of deep-sea fishes. Moreover, given their evolutionary placement, they are critical to investigate the early diversification of the Teleostei. The assembled mitogenome displays the expected gene arrangement for vertebrate mtDNA. Phylogenetic analyses combining all the available mitogenomes of the Order Notacanthiformes were performed. The evolutionary relationships among H. ovenii and the rest of the Halosauridae family were confirmed. This mitogenome provides a valuable baseline for future research of H. ovenii. [ABSTRACT FROM AUTHOR]

Deep-sea fish taxa are elusive, difficult to study, and in multiple cases, represent taxonomic conundrums. Here, we sequenced the complete mitogenome of the shortfin spiny eel, Notacanthus bonaparte, for the first time using low coverage Illumina Paired-end (PE) sequencing. The shortfin spiny eel belongs to the order Notacanthiformes, a relatively unknown taxon of deep-sea marine fishes mostly benthopelagic and bathydemersal. The total length of the assembled mitogenome is 16,623 bp and displays the expected gene orientation for vertebrate mtDNA. Phylogenetic analyses combining all the available mitogenomes of the order Notacanthiformes were performed. The position of N. bonaparte as a member of the Notacanthidae family was confirmed. This mitogenome provides a valuable baseline for future research of N. bonaparte. [ABSTRACT FROM AUTHOR]

The recent advances in molecular biology techniques have prompted the use of vitellogenin (VTG) gene expression as a sensitive and reliable indicator of estrogenic chemicals (EC) exposure. However, data on the dynamic response of the different VTGs genes upon EC exposure is still poorly understood, particularly in sentinel fish species used in field monitoring studies. Hence, the present study aimed at developing a sensitive real-time PCR assay for determining the response of VTG I and II in the recently proposed marine sentinel species Lipophrys pholis upon exposure to the model EC 17α-ethinylestradiol (EE2). The findings of the laboratory study indicate that L. pholis VTG I proved to be not only more inducible but also more sensitive to EE2 exposure than VTG II, for the same range of concentrations. In fact, VTG I gene induction was 475-fold higher than VTG II at 15 ng/L EE2, and 13-fold at 5 ng/L EE2. Overall, the findings of the present study indicate that in the field, expression of VTG I in L. pholis should be preferentially used in the screening of EC exposure because of its higher sensitivity. Furthermore, the present study favors L. pholis integration in monitoring programs associated with EC's pollution within the European water policy legislation. [ABSTRACT FROM AUTHOR]

Many environmental pollutants can exert adverse effects on exposed organisms, including fish, leading to disruption of the endocrine system. Enzymes involved in the sex steroid biosynthesis are potential targets for the toxic action of pollutants. In this context, we investigated the hypothesis that selected estrogenic chemicals-the pharmaceutical estrogen ethinylestradiol (EE2), the phytoestrogen genistein (GEN), and the industrial compound bisphenol A (BPA)-may cause endocrine disruption by directly disturbing steps of fish steroidogenic pathways. We studied the mRNA expression of eight selected genes encoding steroidogenic enzymes (11β-HSD2, 20β-HSD, 3β-HSD1, 17β-HSD1, 17β-HSD8, 17β-HSD12, CYP19a, CYP19b) by quantitative real-time PCR. Testis slices from adult specimens of the model fish Nile tilapia were exposed in vitro for 3 and 8 h either to individual or to mixture solutions of EE2 (100 ng/L), GEN (200 ng/L), and BPA (10 µg/L); all at the peak concentrations observed in the Douro River estuary (Portugal). Our data revealed that only the mixture of the tested chemicals directly induced the expression of 11β-HSD2, 17β-HSD1, and 17β-HSD12, after 8 h, whereas no effect was seen for chemicals tested individually. The gene expression pattern agrees with the concept of dose addition for environmental mixtures, and for the first time an interference of estrogenic EDCs is reported for 17β-HSD1 and 17β-HSD12. [ABSTRACT FROM AUTHOR]