Xuefen Yang

The genus Triplophysa exhibits remarkable adaptability to the unique environment found at the Qinghai-Tibet Plateau (QTP). Higher quality genomes are helpful to the study of the adaptability to the extreme environment in the plateau. This study utilized PacBio HiFi, Ultra-long ONT, and Hi-C sequencing of Triplophysa yaopeizhii to construct the first telomere-to-telomere (T2T) gapless genome assembly of the genus Triplophysa. The genome size is 671.58 Mb, with a contig N50 length of 26.04 Mb. The sequences were anchored onto 25 chromosomes with all centromeres and telomeres. Furthermore, 293.98 Mb (43.77%) of repetitive sequences and 26,487 protein-coding genes were identified. Comparative analyses with the genomes of closely related species demonstrated high completeness, continuity, and accuracy of the genome. The genomic quality was further substantiated by the QV of 31.82 with 96.60% of BUSCO. This study provides a valuable genetic resource of the genus Triplophysa and serves as an essential reference for elucidating the adaptive genetic mechanisms of plateau fish to the high altitude.

To clarify how the digestive tract of the weatherloach, Misgurnus anguillicaudatus, serves a dual function of digestion and respiration simultaneously, the histological structures of its digestive tract, the passage of digesta and air passing through its intestine and the rate of intestinal evacuation have been studied. The results indicate that the digestive tract is divided into five functional regions, i.e., esophagus, anterior intestine, middle intestine, posterior intestine and rectum. The diverse intestinal structures have the specialized function of coordinating digestion and respiration. An X-ray barium meal examination showed in the normal breathing state, the contents of the intestine are diffusely semifluid, and air is distributed as bubbles in the dorsal intestine 2 h after feeding. After 5 h, the contents accumulated in the mid and posterior intestine, and gas flowed above the contents as bundles. After 8 h, the intestinal food was basically evacuated. In the intestinal air-breathing restricted group, the contents of the intestine remained diffuse, and a large number of digesta entered and remained in the rectum after 5 h. After the inhibition was relieved, the contents of the rectum were rapidly discharged. Measurement of the intestinal evacuation rate in the intestine showed that the evacuation of the intestinal contents lagged behind that of the normal group in the air-breathing restricted group. Compared to the normal state and inhibited GAB (gastrointestinal air breathing), we could deduce that GAB could promote the movement of the intestine.

A total of 81,868 All-Unigenes were sequenced and assembled by the transcriptome in the dorsal skin, the lateral skin, and the peritoneal wall layer of Triplophysa stenura with a total assembly length of 123,827,585 bp, and 68,750 unigenes were annotated to seven functional databases. A total of 588 DEGs were screened between the dorsal and lateral skin, 17,097 DEGs were screened between the dorsal skin and the peritoneal wall layer, and 16,598 DEGs were screened between the lateral skin and the peritoneal wall layer. Most of DEGs in three tissues were annotated to GO terms related to cellular structures, binding, cellular processes, and catalytic activity. They were also annotated to KEGG pathways such as the MAPK signaling pathway, PI3K-Akt signaling pathway, Wnt signaling pathway, melanogenesis, tyrosine metabolism, and cell cycle. A total of twenty-three DEGs were found to be enriched in the melanin synthesis pathway by a local Blast comparison, of which nine DEGs were significantly upregulated in the peritoneal wall layer and six DEGs were significantly upregulated in the dorsal and lateral skin. The results suggest that these genes may be associated with the molecular mechanism of melanin synthesis in T. stenura, and the differential regulation of genes may be related to the differences in UVR intensity and tissue sites of melanin synthesis. Further investigation is needed on how these genes specifically regulate melanin synthesis.

To understand the molecular evolution of mitochondrial genomes (mitogenomes) in the genus Odontobutis, the mitogenome of Odontobutis yaluensis was sequenced and compared with those of another four Odontobutis species. Our results displayed similar mitogenome features among species in genome organization, base composition, codon usage, and gene rearrangement. The identical gene rearrangement of trnS-trnL-trnH tRNA cluster observed in mitogenomes of these five closely related freshwater sleepers suggests that this unique gene order is conserved within Odontobutis. Additionally, the present gene order and the positions of associated intergenic spacers of these Odontobutis mitogenomes indicate that this unusual gene rearrangement results from tandem duplication and random loss of large-scale gene regions. Moreover, these mitogenomes exhibit a high level of sequence variation, mainly due to the differences of corresponding intergenic sequences in gene rearrangement regions and the heterogeneity of tandem repeats in the control regions. Phylogenetic analyses support Odontobutis species with shared gene rearrangement forming a monophyletic group, and the interspecific phylogenetic relationships are associated with structural differences among their mitogenomes. The present study contributes to understanding the evolutionary patterns of Odontobutidae species.

Water samples and sediment cores were taken at 5 sites of Nanhu Lake, Wuhan to investigate the seasonal dynamics of phosphorus in water body, sediments and their interstitial water, as well as the phosphorus forms in sediments. The results showed that the average concentrations of total phosphorus (TP) and orthophosphate (PO4(3-) -P) in water body were 0.240 and 0.033 mg x L(-1), respectively, with the highest concentrations of TP and PO4(3-)-P in November and the lowest concentration of TP and of PO4(3-) -P in February and August, respectively. The concentration of TP in sediments was averagely 1.005 mg x g(-1), being increased from April to November and becoming stable from November to February, and decreased with sedimentation depth. The concentration of PO4(3-) -P in interstitial water was 0.209 mg x L(-1) on average, being the highest in November and the lowest in February, with the same vertical distribution pattern like TP in sediments. The dominant form of phosphorus in sediments was inorganic phosphorus (IP), occupying 61.4%-77.1% of total extracted phosphorus. The concentration of bio-available phosphorus (BA-P) in sediments was very high, but decreased significantly with sedimentation depth. According to the significant correlations between phosphorus forms in sediments and PO4(3-) -P in interstitial water, the BA-P and auto-calcium bound phosphorus (ACa-P) in sediments should be the main P sources released from sediments to water body.