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The gut microbiome is thought to play vital roles in host fitness and local adaptation to new environments, thereby facilitating the invasion of the host species. The Nile tilapia (Oreochromis niloticus) (NT) is an aggressive and omnivorous species that competes with native fishes for food resources, and it has successfully invaded much of the Pearl River basin in China. Here, we investigated the gut microbiomes of invasive Nile tilapia and indigenous black Amur bream (BA) in the same river section using high-throughput 16S rRNA gene sequencing. The results indicated that the gut microbiome of NT had several special characteristics, e.g., higher alpha diversity and greater niche breadth, compared with the bream. The gut microbiota of the small size of Nile tilapia (NTS) and small size of black Amur bream (BAS) groups were dominated by Proteobacteria, while those of the NTS and large size of Nile tilapia (NTL) and BAS and large size of black Amur bream (BAL). BAL and NTL were characterized by Firmicutes and Fusobacteriota, respectively. We found that Pseudomonas, Cetobacterium, Ralstonia, and Romboutsia were biomarkers of the NTS, NTL, BAS, and BAL groups, respectively. Moreover, the results collectively suggested that the clustering coefficients of BAL and NTL networks were greater than those of BAS and NTS networks, and BAS had the smallest network among the four groups. Positive interactions between two ASVs dominated the BAS, NTS, and NTL networks, while the proportion of negative interactions between two ASVs in the BAL network was remarkably increased. Low levels of interspecies competition in the NT gut microbiome would contribute to high diversity in the dietary niches and would also benefit the survival and local adaptation of the host. Our results identified specific biomarkers of gut microbial species in invasive Nile tilapia and provided useful information concerning how to monitor and manage invasive Nile tilapia populations.

Abstract Determining the temporal community composition of fish eggs in particular regions and understanding the reproductive times of regional fish taxa are key aspects of the management and regulation of regional fish stocks. However, it is extremely difficult to accurately identify fish eggs due to the absence of diagnostic morphological characters. We sampled fish eggs in the lower Hongshuihe River (an upper mainstem of the Pearl River) between May and September 2020. We then used DNA barcoding to determine the species composition of the egg pool and to predict the spawning periods of the identified species. A total of 641 eggs and 17 larvae were chosen for molecular identification; 397 eggs and 17 larvae yielded high‐quality barcoding sequences. The high failure rate (~38%) was most likely due to long‐term storage in low concentrations of ethanol prior to molecular analysis. We successfully classified 392 eggs into 10 species and 13 larvae into four species using public databases. Most of the species identified in the egg pool were small and/or benthic, and migratory species were rare. This may partially reflect the adverse effects of hydropower cascade development in this river section. We also found that spawning periods tended to be species‐specific. Our study provides a reference for the conservation and management of regional fishery stocks.

Abstract Genome complexity such as heterozygosity may heavily influence its de novo assembly. Sequencing somatic cells of the F1 hybrids harboring two sets of genetic materials from both of the paternal and maternal species may avoid alleles discrimination during assembly. However, the feasibility of this strategy needs further assessments. We sequenced and assembled the genome of an F1 hybrid between Silurus asotus and S. meridionalis using the SequelII platform and Hi-C scaffolding technologies. More than 300 Gb raw data were generated, and the final assembly obtained 2344 scaffolds composed of 3017 contigs. The N50 length of scaffolds and contigs was 28.55 Mb and 7.49 Mb, respectively. Based on the mapping results of short reads generated for the paternal and maternal species, each of the 29 chromosomes originating from S. asotus and S. meridionalis was recognized. We recovered nearly 94% and 96% of the total length of S. asotus and S. meridionalis. BUSCO assessments and mapping analyses suggested that both genomes had high completeness and accuracy. Further analyses demonstrated the high collinearity between S. asotus, S. meridionalis, and the related Pelteobagrus fulvidraco. Comparison of the two genomes with that assembled only using the short reads from non-hybrid parental species detected a small portion of sequences that may be incorrectly assigned to the different species. We supposed that at least part of these situations may have resulted from mitotic recombination. The strategy of sequencing the F1 hybrid genome can recover the vast majority of the parental genomes and may improve the assembly of complex genomes.

Teleost omnivorous fish that coexist partially sharing resources are likely to modify their gut traits and microbiome as a feedback mechanism between ecological processes and evolution. However, we do not understand how the core gut microbiome supports the metabolic capacity of the host and regulates digestive functions in specialized omnivorous fish gut traits. Therefore, we evaluated the gut microbiome of eight omnivorous fish from a single family (i.e., Cyprinidae) in the current study. We examined the correlation between host phylogeny, diet composition, and intestinal morphological traits related to the intestinal microbiome. The results indicated that cyprinid fish with similar relative gut lengths had considerable gut microbiome similarity. Notably, the SL (short relative gut length) group, as zoobenthos and zooplankton specialists, was abundant in Proteobacteria and was less abundant in Firmicutes than in the ML (medium relative gut length) and LL (long relative gut length) groups. These fish could extract nutrients from aquatic plants and algae. Additionally, we found the relative abundance of Clostridium and Romboutsia to be positively correlated with host relative gut length but negatively correlated with the relative abundance of Cetobacterium, Plesiomonas, Bacteroides, and Lactobacillus, and host-relative gut length. We also show a positive linear relationship between host gut microbiome carbohydrate metabolism and relative gut length, while the amino acid and lipid metabolism of the gut microbiome was negatively correlated with host-relative gut length. In addition, omnivorous species competing for resources improve their ecological adaptability through the specialization of gut length, which is closely related to variation in the synergy of the gut microbiome. Above all, specialized gut microbiota and associated gut morphologies enable fish to variably tolerate resource fluctuation and improve the utilization efficiency of nutrient extraction from challenging food resources.

Global warming is influencing the life history traits of fishes globally. However, the impacts of elevated temperature on fish reproduction are diverse in different regions. Previous studies have revealed that the spawning timing of silver carp (Hypophthalmichthys molitrix) in the Pearl River, in China, has changed over the past decade. However, few studies have explored the potential reasons, which are critical for determining fishing-moratorium periods and developing sustainable fisheries. The current study used discharge suitability index (DSI), temperature suitability index (TSI), correlation and time-series analyses to determine (i) the optimal discharge and temperature for silver carp spawning; (ii) relationships among the thermal regime, hydrological parameters, and spawning timing based on an 11-year time-series dataset. Our results indicated that the most suitable discharge and temperature for silver carp spawning were 13,000–15,000 m3/s and 25–26°C, respectively. The start date of spawning fluctuated with a slight tendency to delay, while the spawning peak and end date obviously occurred earlier during the study period. Correlation analyses suggested that the increasing average temperature between January and March likely caused the initial spawning delay. Moreover, elevated temperatures in August and September probably promoted the anticipated end of silver carp spawning. However, increases in discharge did not significantly correlate with the start of spawning but were significantly and positively correlated with the spawning peak. These results indicated that elevated temperatures shorten the spawning period of silver carp in the Pearl River. Moreover, the initial spawning of silver carp seems to be triggered by temperature rather than changes in discharge; flow pulses can probably create more suitable spawning niches for H. molitrix. This study enhances our understanding of the effect of warming on fish reproduction in subtropical regions.

River dynamics have been hypothesized to substantially influence the genetic structure of freshwater fish taxa. Southern China harbors abundant independent river systems, which have undergone historical rearrangements. This river system is thus an excellent model with which to test the abovementioned hypothesis. In this study, a cyprinid widespread in many independent rivers in southern China, Toxabramis houdemeri, was chosen as an exemplar species with which to explore the effects of river configuration changes on spatial genetic structure using mitochondrial and nuclear markers. The results indicated that the T. houdemeri populations fell into four mitochondrial haplotype groups, each genetically endemic to a single river or two adjacent river systems. The mitochondrial haplotype network recovered a clear genetic boundary between Hainan Island populations and mainland populations. Notable genetic differentiation was observed within populations from distinct river systems in both mitochondrial and nuclear loci. River system separation, mountain barriers, and mobility were the key factors shaping the genetic structure of T. houdemeri populations. Late Pleistocene divergence and historical immigration were identified within the four mitochondrial haplotype groups, indicating that river rearrangements triggered by the Late Pleistocene glacial cycles were important drivers of the complex genetic structure and demographic history of T. houdemeri. Historical demographics suggested that T.houdemeri populations expanded during the Late Pleistocene. The present study has important consequences for the management and conservation of T. houdemeri.

The Pearl River is a global hotspot of fish biodiversity, yet has the most threatened endemic fish species in China. Since the establishment of the Changzhou Dam in the lower reach, changes in hydrological rhythm have negatively impacted fish downstream of the dam, but their spatiotemporal distribution in response to flood alteration has received little attention. In this study, hydroacoustic surveys were undertaken monthly in 2016 to monitor the distribution and behavior of fish. Fish densities were higher during the water discharge rising stage than during the falling stage, indicating that the fish aggregate during flooding (coefficient of variation [CV] > 100%) and depart after flooding (CV < 100%), especially aggregations of large fish. The target strength (TS) was allocated to two groups as per their frequency distributions, defined as small fish (−55 dB < TS < −40 dB) and large fish (TS > −40 dB). The sizes of both groups were significantly larger during the rising stage when compared to those during the falling stage (p < 0.01). Comparatively more fish were present with a greater average TS, and a substantially greater proportion of large fish was detected during rising stages. Hydrological variation importantly influences fish aggregations, including the numbers and sizes present, with the differences being particularly pronounced between the rising and falling stages. Combined with relevant studies, it is suggested that water releases from the Changzhou Dam should be regulated to satisfy fish spawning and migration demands during the main breeding season.

Pseudobagrus gracilis is an endemic bagrid catfish in the Pearl River. To date, sparse studies conducted on this species have blocked our understanding of this species. In this study, the complete mitochondrial genome of P. gracilis was sequenced and reported using Illumina MiSeq platform. The P. gracilis mitogenome was 16,527 bp in length and comprised 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and one control region (D-loop). Its overall nucleotide base composition was 31.0% (A), 15.6% (G), 26.3% (C), and 27.1% (T), with an AT content 58.1%. Phylogenetic analyses based on Neighbor-joining approach revealed that Pseudobagrus species formed three lineages (I, II and III) and P. gracilis had close relationship with P. emarginatus, P. pratti and P. truncatus.

In this study, the complete mitochondrial genome of Carassioides acuminatus was first sequenced and annotated. The entire mitogenome is 16,579bp in length, which consists of 13 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes, and a control region (D-loop). The overall nucleotide composition of the C. acuminatus mitochondrial genome shows an obvious anti-G bias. The accuracy of the fresh sequences was verified by phylogenetic analysis. The complete mitochondrial genome of C. acuminatus is useful to population genetics and molecular systematics.

Understanding fish migration patterns and habitat use is essential for fisheries management. We conducted an acoustic fine-scale tracking experiment from March to June 2017 to determine the common carp movement pattern and habitat use in the downstream area of the Pearl River. The eight tagged common carp were detected for 39.38 ± 29.57 d, on average, with a total average detection period of 42.12 ± 28.02 d. A general linear mixed model suggested they were detected more during the night than during the day. Common carp preferred habitats near the sandbar and riparian shallow habitats, as revealed by their movement tracks and habitat selection indexes. The general additive mixed model (GAMM) analysis of their shortest distances to riverbanks and depth indicated that they migrated to shallower riparian habitat more frequently during the night than during the day. The continuous wavelet spectrum further confirmed the significant diel pattern of their vertical movement. Their habitat use was also influenced by the water temperature, water level, and river discharge, as suggested by the GAMM. Our results provide novel information on common carp spatiotemporal movement and habitat use patterns, and have important implications for its native population restoration and the invasive population control/exclusion.

The genus Silurus, an important group of catfish, exhibits heterogeneous distribution in Eurasian freshwater systems. This group includes economically important and endangered species, thereby attracting considerable scientific interest. Despite this interest, the lack of a comprehensive phylogenetic framework impedes our understanding of the mechanisms underlying the extensive diversity found within this genus. Herein, we analyzed 89 newly sequenced and 20 previously published mitochondrial genomes (mitogenomes) from 13 morphological species to reconstruct the phylogenetic relationships, biogeographic history, and species diversity of Silurus. Our phylogenetic reconstructions identified eight clades, supported by both maximum-likelihood and Bayesian inference. Sequence-based species delimitation analyses yielded multiple molecular operational taxonomic units (MOTUs) in several taxa, including the Silurus asotus complex (four MOTUs) and Silurus microdorsalis (two MOTUs), suggesting that species diversity is underestimated in the genus. A reconstructed time-calibrated tree of Silurus species provided an age estimate of the most recent common ancestor of approximately 37.61 million years ago (Ma), with divergences among clades within the genus occurring between 11.56 Ma and 29.44 Ma, and divergences among MOTUs within species occurring between 3.71 Ma and 11.56 Ma. Biogeographic reconstructions suggested that the ancestral area for the genus likely encompassed China and the Korean Peninsula, with multiple inferred dispersal events to Europe and Central and Western Asia between 21.78 Ma and 26.67 Ma and to Japan between 2.51 Ma and 18.42 Ma. Key factors such as the Eocene-Oligocene extinction event, onset and intensification of the monsoon system, and glacial cycles associated with sea-level fluctuations have likely played significant roles in shaping the evolutionary history of the genus Silurus. [ABSTRACT FROM AUTHOR]

Common carp (Cyprinus carpio) is an important valuable cyprinid in China and has been a popular cultured aquaculture species around the globe. Understanding the genetic diversity of wild native common carp not only provides basic data for the protection and utilisation of common carp resources but also assesses the effect of human activities on the genetic diversity of this species. In this study, genetic diversity and population structure of the common carp from 15 sampling populations in the Pearl River and Nandujiang River were determined using a coalescent mitochondrial locus (MLS), including mitochondrial cytochrome b gene (Cytb) and a control region (D‐loop) segment. The haplotype diversity and nucleotide diversity were 0.962 and 0.00628 in the Pearl River and 0.808 and 0.00376 in the Nandujiang River, respectively. Phylogenetic and haplotype network analyses indicated that three sub‐species (a) C. c. rubrofuscus, (b) C. c. haematopterus and (c) C. c. carpio all occur in both rivers. AMOVA revealed that the variation within populations (86.2%) was the main source of the total variation. Statistically significant genetic differentiation among different Pearl River populations of C. c. rubrofuscus (Fst = 0.05–0.25) and relatively high genetic differentiation between the Nandujiang River population and the Pearl River populations (Fst > 0.238) are apparent. Bayesian clustering analyses detected that global populations consisted of eight genetic clusters and examined that Nandujiang River population included relatively pure genetic clusters. Neutrality tests suggested that native populations experienced recent population expansion, and Extended Bayesian Skyline Plot indicated that the common carp populations likely experienced a historical expansion during 0.125–0.250 MYA. Artificial fish propagation and release, escape from fish farms and Fang Sheng may explain the invasion of non‐native sub‐species in many river sections, such as Laibin, Rongjiang, Huizhou, Heyuan and Zhaoqing. To conserve the native common carp populations, release station should be established to culture native common carp fry. Overall, the findings can be contributed to complementing scientific knowledge for conservation and management of the wild native common carp. [ABSTRACT FROM AUTHOR]

Cirrhinus molitorella is one of the most important commercial fish species in the Pearl River, but there are few published studies on the early growth of this species. In the present study, seasonal recruitment patterns, temporal variations in early growth rates and environmental variables were analysed. In all, 1512 individuals were collected during monthly sampling from July 2015 to January 2016, ranging from 30.8- to 84.9-mm standard length (SL). A subsample of 276 juveniles was aged from 68 to 193 days, with hatch dates between 2 February and 19 September, by determining daily increments in otoliths. Monthly abundance data and SL frequency distributions showed that there were two major temporal cohorts of juvenile recruitment, which hatched primarily in April and July. Average growth rate, estimated by the linear relationship between age and SL, was greater for the April cohort (0.49 mm day-1) than the July cohort (0.37 mm day-11). Mean increment widths from the 23rd increment onwards were significantly greater for the April than July cohort (P < 0.05). The slower growth observed in the July cohort was probably due to poorer food availability caused by high river discharge volumes. These results are important for predicting recruitment dynamics and managing the C. molitorella fishery. [ABSTRACT FROM AUTHOR]

Introduction: A prediction model for the 1-, 3-, and 5-year survival rates of metastatic colon cancer (mCC) patients was developed by analyzing important risk factors for the prognosis of mCC patients based on the SEER database.Method: The characteristic of 10,946 patients diagnosed with mCC between 2010 and 2015 was obtained from the SEER database. The population was randomly divided into a training cohort and an internal validation cohort in a 7:3 ratio. Univariate and multivariate cox for independent predictors of mCC prognosis were performed, and nomogram was constructed. The accuracy of the model was verified by calibration curves, ROC curves, and C-index, and the clinical utility of the model was analyzed using decision analysis curves.Result: Age, primary site, grade, surgery, and other eight factors were significantly associated with the prognosis of mCC patients, and these predictors were included in the construction of the nomogram. The C-index was 0.731 (95% CI 0.725–0.737) and 0.736 (95% CI 0.726–0.746) for the training cohort and the validation set, respectively. The results of the ROC curve analysis indicated that the area under the curve (AUC) exceeded 0.7 for both the training cohort and the validation set at 1, 3, and 5 years.Conclusion: The constructed prediction model had an excellent predictive accuracy, which will help clinical decision-making of mCC patients after surgery and individualized treatment.

Length-weight relationships (LWRs) were estimated for four fish species [Spinibarbus hollandi (Oshima, 1919), Distoechodon tumirostris (Peters, 1881), Bangana decora (Peters, 1881), Ptychidio longibarbus (Fang, 1981)] from Liujiang River, China. Fishes were collected from local fish markets that using various fishing gears such as gillnets, castnets and shrimp cages in July and December 2018. The LWRs parameters a and b values for the four species varied 0.008861-0.02018 and 3.041-3.367. New maximum standard lengths for one species was presented in this paper. And the LWRs for two species: Bangana decora and Ptychidio longibarbus is reported for the first time. The result will be very helpful in fisheries management and species conservation. [ABSTRACT FROM AUTHOR]

Abstract: Based on the analysis and deduction of the respective advantages and disadvantages between the traditional teaching methods and computer-aided teaching methods, we explore and summarize the teaching strategies and implementation of the complementary advantages between the traditional teaching methods and computer-aided teaching methods. We think that computer- aided teaching and traditional teaching have their own unique function and that they have their own advantages and disadvantages which cannot replace each other. We cannot simply replace and negate the use of the former to the latter. And in turn, we cannot deny or replace the latter to the former. They should be mutually learn from each other and complement each other. The means of improving teaching quality and effectiveness is not simply the traditional teaching methods, or merely the multimedia teaching mode, but their organic combination. Only well dealing with the relationship between the traditional teaching mode and computer-aided teaching mode based on the teaching concept, combining their characteristics, can achieve the full effect of improving teaching quality and purpose. [Copyright &y& Elsevier]