Characiformes is a diverse and evolutionarily significant order of freshwater fish encompassing over 2,300 species. Despite its diversity, our understanding of Characiformes\' evolutionary relationships and adaptive mechanisms is limited due to insufficient genome sequences. In this study, we sequenced and assembled the genomes of four Characiformes species, three of which were chromosome-level assemblies. Our analyses revealed dynamic changes in gene family evolution, repeat sequences and variations in chromosomal collinearity within these genomes. With the assembled genomes, we were not only able to elucidate the evolutionary relationship of the four main orders in Otophysi but also indicated Characiformes as the paraphyletic group. Comparative genomic analysis with other available fish genomes shed light on the evolution of genes related to tooth development in Characiformes. Notably, variations in the copy number of secretory calcium-binding phosphoproteins (SCPP) genes were observed among different orders of Otophysi, indicating their potential contribution to the diversity of tooth types. Our study offers invaluable genome sequences and novel insights into Characiformes\' evolution, paving the way for further genomic and evolutionary research in fish.

Triploidization plays an important role in aquaculture and surrogate technologies. In this study, we induced triploidy in the matrinxã fish (Brycon amazonicus) using a heat-shock technique. Embryos at 2 min post fertilization (mpf) were heat shocked at 38°C, 40°C, or 42°C for 2 min. Untreated, intact embryos were used as a control. Survival rates during early development were monitored and ploidy status was confirmed using flow cytometry and nuclear diameter analysis of erythrocytes. The hatching rate reduced with heat-shock treatment, and heat-shock treatments at 42°C resulted in no hatching events. Optimal results were obtained at 40°C with 95% of larvae exhibiting triploidy. Therefore, we report that heat-shock treatments of embryos (2 mpf) at 40°C for 2 min is an effective way to induce triploid individuals in B. amazonicus.

The Dotted Gizzard Shad (Konosirus punctatus) was one of the most important commercial fish species in China, Japan and Korea. In this study, the complete mitochondrial genome of K. punctatus was presented. The full length of the mitochondrial genome was 16,705 bp, including 13 protein-coding genes (PCGs), two ribosomal RNAs, 22 transfer RNA genes, one non-coding control region (CR) and one origin of replication on the light-strand. The total nucleotide composition of mitochondrial DNA was 25.79%A, 25.09%T, 29.05%C, 20.08%G, and AT was 50.88%. The mitochondrial genome provides an important resource for solving taxonomic problems and studying molecular evolution.

In this study, the complete mitochondrial genome of Hyphessobrycon herbertaxelrodi is presented, and we also discussed its mitochondrial characteristics. The full length of the mitochondrial genome was 17,417 bp, including 13 protein coding genes (PCGs), 2 ribosomal RNAs (12S and 16S), 22 transfer RNA genes, 1 non-coding control region (D-loop), and 1 origin of replication on the light-strand. The total nucleotide composition of mitochondrial DNA was 29.76%A, 29.88%T, 25.35%C, 15.01%G, and AT was 59.64%. The phylogenetic tree suggested that H. herbertaxelrodi shared the most recent common ancestor with Astyanax giton, Grundulus bogotensis, Astyanax paranae, and Oligosarcus argenteus.

The presence of intermuscular bones in fisheries products limits the consumption and commercialization potential of many fish species, including tambaqui (Colossoma macropomum). These bones have caused medical emergencies and are an undesirable characteristic for fish farming because their removal is labor-intensive during fish processing. Despite the difficulty in identifying genes related to the lack of intermuscular bone in diverse species of fish, the discovery of individuals lacking intermuscular bones in a Neotropical freshwater characiform fish has provided a unique opportunity to delve into the genetic mechanisms underlying the pathways of intermuscular bone formation. In this study, we carried out a GWAS among boneless and wt tambaqui populations to identify markers associated with a lack of intermuscular bone. After analyzing 11 416 SNPs in 360 individuals (12 boneless and 348 bony), we report 675 significant (Padj  < 0.003) associations for this trait. Of those, 13 associations were located near candidate genes related to the reduction of bone mass, promotion of bone formation, inhibition of bone resorption, central control of bone remodeling, bone mineralization and other related functions. To the best of our knowledge, for the first time, we have successfully identified genes related to a lack of intermuscular bones using GWAS in a non-model species.

Mitochondrial genome sequencing has become widely used in numerous fields, including systematics, phylogeny, and evolutionary genomics. To elucidate phylogenetic relationships among members of the family Characidae, we sequenced the mitogenomes of four species within this family, namely, Aphyocharax rathbuni, Hyphessobrycon herbertaxelrodi, Hyphessobrycon megalopterus, and Prionobrama filigera. The mitogenomes were found to be 16,678-16,841 bp and encode 37 typical mitochondrial genes (13 protein-coding, 2 ribosomal RNA, and 22 transfer RNA genes). Gene arrangements in the studied species are consistent with those in the inferred ancestral fish. Most protein-coding genes in these mitogenomes have typical ATN start codons and TAR or an incomplete stop codon T-. Phylogenetic relationships based on Bayesian inference and maximum-likelihood methods indicated that A. rathbuni, H. herbertaxelrodi, H. megalopterus, and P. filigera belong to the Characidae family. Of the 15 Characidae species studied, three pairs were of the same genus, but the results for only one pair were well supported. This phylogenetic classification is inconsistent with those described in previous morphological and taxonomic studies on this family. Thus, systematic classification of the Characidae requires further examination. Our findings yield new mitogenomic data that will provide a basis for future phylogenetic and taxonomic studies.

This study investigated whether a meridian-like distribution of Alcian blue (AB) existed after it was injected into a fish\'s body and suggested a new animal model for meridian study. Twenty Gephyrocharax melanocheir fish with translucent bodies were injected with AB at a point near the spinal column or the dorsal fin. Distribution of AB was observed using a digital camera and a stereomicroscope. Three or more obvious blue tracks were found: one along the spinal column, another along the posterior margin of the abdomen extending to the superior margin of the anal fin, and a third along both sides of the dorsal fin. They were similar to the locations of the governor, conceptual vessel, and urinary bladder meridians, respectively, on the human body according to the classic theory of traditional Chinese medicine. A few other blue tracks were also found, which apparently did not correspond to any known meridians. The results show that the tracks of AB share important similarities with the locations of classically described meridians and that they are mainly distributed in the interstitial space around bones and blood vessels and inside muscular interstices. This study may provide a new experimental animal model for exploring acupuncture meridians.

Colossoma macropomum (Cuvier, 1816) is the largest characin of South America. This species and its congeners mainly feed on zooplankton, insects, snails and decaying plants. In this paper, we sequenced and annotated the complete mitogenome of C. macropomum. The total length is 16,703 bp, and it typically consist of 37 genes, including 13 protein-coding genes, two rRNAs, 22 tRNA, a light-strand replication origin (OL) and a large control region (D-loop). The overall base composition is 29.9%, 24.6%, 29.5% and 15.9% for A, T, C and G, respectively, with a slight bias on AT content (54.6%). All protein-coding genes share the start codon ATG, except for COI, which begins with GTG. Most of them have TAA or TAG as the stop codon, except COII, ND4 use AGA and COI, Cytb use an incomplete stop codon T. This information could provide useful molecular data and contribute to further phylogenetic studies of Characiformes and Serrasalmidae.

We first sequenced the complete mitochondrial genome of silvertip tetra (Hasemania nana). The mitogenome was determined to be 16,581 bp long circular molecule with a typical gene arrangement of vertebrate mitochondrial DNA. All genes were encoded on the heavy strand with the exception of ND6 and eight tRNA genes. Mitochondrial DNA information provided the basis for the studies in species identification and conservation of the species\' natural resources.

This study investigated the molecular mechanisms of polypeptides from Chlamys farreri (PCF)\'s anti-apoptotic effects in ultraviolet A-rays (UVA) exposed HaCaT cells. UVA-induced apoptosis in HaCaT cells was confirmed with Hoechst 33258 fluorescent staining; PCF treatment inhibited UVA-induced apoptosis in HaCaT cells, increased transcriptional activities of heat shock factor protein 1 (HSF1) and the expression of heat shock protein 70 (HSP70), whereas inhibited activation of c-Jun N-terminal kinases (JNK), expression of xanthine oxidese (XO), inducible nitric oxide synthase (iNOS) and release of nitric oxide (NO)/reactive oxygen species (ROS). Meanwhile, the HSF1 transcription inhibitor quercetin increased UVA-induced apoptosis, activation of JNK, expression of XO and iNOS and release of NO/ROS. Among the two NO release peaks we found in UVA exposed HaCaT cells, XO inhibitor oxypurinol was found to be able to inhibit NO release at 3h post UVA exposure but not 18h, while iNOS inhibitor S-methylisothiourea sulfate (SMT) was found to inhibit iNOS expression and NO release at 18h but not 3h. PCF\'s protection against UVA-induced apoptosis in HaCaT cells involves increased transcriptional activity of HSF1, increased expression of HSP70, and the subsequential inhibition of JNK pathway, XO and iNOS expression and ROS/NO release.