Chinese Longsnout Catfish Leiocassis Longirostris Research Articles

Identification of male sex-specific markers using genome re-sequencing in the Chinese longsnout catfish Leiocassis longirostris

The Chinese longsnout catfish (Leiocassis longirostris Günther), an indigenous commercially important fish species in China, exhibits markedly sex dimorphism in growth, which the males grow much faster than females. So, we aimed to develop sex-specific DNA markers to accelerate the development of sex control techniques for L. longirostris. In this study, 15 individuals of each sex were sequenced using whole-genome re-sequencing technology. A total of 238.51 Gb clean data was used to detect the sex associated markers and we found that 2472 loci were enriched in the first 18 Mb of Chr 7, the putative sex-determination region for L. longirostris. All candidate markers were male heterozygous, implying that the sex-determination system of the L. longirostris is the XX/XY type. Using the sequence polymorphism of male and female individuals in this region, we designed six pairs of primers to develop sex-specific markers, of which three markers exclusively exhibited male-specific bands. Further validation showed that the accuracy of sex prediction was up to 100% for individuals in the Meishan, Chengdu, Yibin and Shishou regions, suggesting wide applicability among local populations. Importantly, marker 3 was located in the ACAP1 gene, which may be involved in sex determination or differentiation of L. longirostris. This method for developing sex-specific markers is efficient, simple, and provides a useful reference that can be applied to other fish species. The markers developed in this work could be instrumental for sex control breeding to increase the yield in the L. longirostris aquaculture industry.

Molecular characteristics, polymorphism and expression analysis of mhc Ⅱ in yellow catfish(pelteobagrus fulvidraco)responding to Flavobacterium columnare infection

The major histocompatibility complex (MHC) is an important component of the immune system of vertebrates, which plays a vital role in presenting extrinsic antigens. In this study, we cloned and characterized the mhc ⅡA and mhc ⅡB genes of yellow catfish Pelteobagrus fulvidraco. The open reading frames (ORFs) of mhc ⅡA and mhc ⅡB genes were 708 bp and 747bp in length, encoding 235 and 248 amino acids, respectively. The structure of mhc ⅡA and mhc ⅡB includes a signal peptide, an α1/β1 domain, an α2/β2 domain, a transmembrane region and a cytoplasmic region. Homologous identity analysis revealed that both mhc ⅡA and mhc ⅡB shared high protein sequence similarity with that of Chinese longsnout catfish Leiocassis longirostris. mhc ⅡA and mhc ⅡB showed similar expression patterns in different tissues, with the higher expression level in spleen, head kidney and gill and lower expression in liver, stomach, gall bladder and heart. The mRNA expression level of mhc ⅡA and mhc ⅡB in different embryonic development stages also showed the similar trends. The higher expression was detected from fertilized egg to 32 cell stage, low expression from multicellular period to 3 days post hatching (dph), and then the expression increased to a higher level from 4 dph to 14 dph. The mRNA expression levels of mhc ⅡA and mhc ⅡB were significantly up-regulated not only in the body kidney and spleen, but also in the midgut, hindgut, liver and gill after challenge of Flavobacterium columnare. The results suggest that Mhc Ⅱ plays an important role in the anti-infection process of yellow catfish P. fulvidraco.

Histological Observations and Regeneration of Barbels in Juveniles of the Chinese Longsnout Catfish Leiocassis longirostris

Barbel structure and regenerated barbel length in the juvenile Chinese longsnout catfish Leiocassis longirostris (G<TEX>$\ddot{u}$</TEX>nther), were evaluated. The barbles consisted of an epidermis, a dermis, and a central rod. The epidermis harbored taste buds, granular cells and epidermal cells. The taste buds were basophilic and situated along the distal portion of the epidermis. The dermis was composed of loose connective tissue containing blood vessels pigment cells. The innermost central region was cartilage enclosed within layers of muscle layers. After 30 days, the regenerated barbel length measured <TEX>$0.92{\pm}0.404mm$</TEX> at <TEX>$15^{\circ}C$</TEX> (regenerated growth curve: y = 0.5085x + 4.0678, <TEX>$r^2$</TEX> = 0.9654, where y is regenerated length and x is experimental period in days), <TEX>$1.88{\pm}0.521mm$</TEX> at <TEX>$20^{\circ}C$</TEX> (y = 0.1806x + 4.808, <TEX>$r^2$</TEX> = 0.9822), and <TEX>$6.44{\pm}0.751mm$</TEX> at <TEX>$25^{\circ}C$</TEX> (y = 0.0914x + 4.9918, <TEX>$r^2$</TEX> = 0.9944). Fifteen days after amputation, the regenerated length was significantly longer at <TEX>$25^{\circ}C$</TEX> than at 15 or <TEX>$20^{\circ}C$</TEX> (P < 0.05). The barbels of the Chinese longsnout catfish was the tender and flexible type, and our experimental findings provide evidence of temperature-dependent regeneration. Additional investigation of the behavior and physiology of the Chinese longsnout catfish is needed, particularly histological studies of regenerated barbels and the measurements of the numbers of taste buds per barbel under various environmental conditions.

Genetic variation of the Chinese longsnout catfish Leiocassis longirostris in the Yangtze River revealed using mitochondrial DNA cytochrome b sequences

The mitochondrial DNA cytochrome b of 132 Leiocassis longirostris collected from 12 localities in the upper to lower reaches of the Yangtze River were amplified and partially sequenced using the PCR technique. The results showed that 27 nucleotide sites were variable along 817bp length of homologous sequence (3.3%), base substitutions happened mostly at the third codon position. A total of 22 haplotypes were identified, which were characterized with moderate haplotype diversity (h=0.5417±0.0519), but low nucleotide diversity (π=0.0019±0.0012). Median-joining network analysis revealed star-shaped patterns with one common central haplotype (H3), whereas mismatch distribution analysis found that the Chinese longsnout catfish fitted a smooth unimodal distribution, which suggested that this species underwent population expansion following bottlenecks and/or they originated from a small number of founding individuals. The time that the total population of Chinese longsnout catfish in the Yangtze River expanded was estimated 169,000–337,000years before present. The analysis of molecular variance (AMOVA) and phylogenetic reconstructions did not detect significant geographic structure between different river sections, especially between above and below the Gezhouba Dam and the Three Gorges Dam, which suggested that these recently developed dams might have not significantly resulted in population genetic differentiation in the Chinese longsnout catfish.

Genetic variation at mtDNA and microsatellite loci in Chinese longsnout catfish (Leiocassis longirostris)

Genetic variability and population structure of the Chinese longsnout catfish Leiocassis longirostris Günther in the Yangtze River was examined with mitochondrial control region sequences and nuclear microsatellite markers. A 705-bp segment of the mitochondrial DNA control region was sequenced from 132 samples, which identified a total of 61 haplotypes. The Chinese longsnout catfish in the Yangtze River was characterized with high haplotype diversity (h=0.9770±0.0041) but low nucleotide diversity (π=0.0081±0.0043). Median-joining network analysis revealed a star-shaped pattern and mismatch distribution analysis found a smooth unimodal distribution, which suggested that this species in the Yangtze River underwent a population expansion following bottlenecks and/or they originated from a small size of founding population. It was estimated that the possible time of population expansion was 139,000-435,000years before present, a time period in the middle Pleistocene. The analysis of molecular variance and phylogenetic reconstructions did not detect significant geographic structure between different river sections. This pattern of genetic variation was further evidenced with nuclear microsatellite markers. The genetic differentiation between above and below the Gezhouba Dam and Three Gorges Dam is very small at mitochondrial and nuclear levels, which suggested that these recently developed dams might have not significantly resulted in population genetic fragmentation in the Chinese longsnout catfish. However, the potential exacerbation of genetic structuring by the dams should not be overlooked in the future.

The complete mitochondrial genome of the Chinese longsnout catfish Leiocassis longirostris (Siluriformes: Bagridae) and a time-calibrated phylogeny of ostariophysan fishes

The complete mitogenome sequence of the Chinese longsnout catfish Leiocassis longirostris was determined using long-polymerase chain reaction (long-PCR) and directly sequenced with primer walking method. The complete mtDNA was 16,534 bp in length and contained 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and a control region (D-loop), the gene composition/order of which was identical to that observed in most other vertebrates. Phylogenetic relationship of 15 ostariophysan fishes was reconstructed using Bayesian inference and maximum likelihood methods based on a total of 15,658 nucleotides from all the 13 protein-coding, two rRNA, and 22 tRNA genes, using recently developed models of rate autocorrelation, which resolved the phylogenetic relationship of the major ostariophysan lineages with a high statistical support. The present result was consistent with some previous molecular cladistic work which supported the grouping of (((((Characiformes, Gymnotiformes), Siluriformes), Cypriniformes), Gonorynchiformes), outgroup). The Chinese longsnout catfish together with the Bagrid catfish (both from the same family Bagridae) had a closer affinity with Amblycipitidae than with other four analyzed catfish families. The relaxed molecular clock method incorporated into the program BEAST vl.5.3 was used to estimate divergence dates among ostariophysan lineages, which revealed that the major ostariophysan lineages diversified in the middle Jurassic (around 164.5 million years ago (Mya)) and the split of Leiocassis/Pseudobagrus occurred in the Oligocene to Miocene (8.9-25.1 Mya). The time-calibrated tree generated in this study would provide a powerful evolutionary tool for broad-scale comparative studies of the catfishes and the ostariophysan fishes.