Hatchery-reared enhancement program for silver carp (Hypophthalmichthys molitrix) in the middle Yangtze River: monitoring the effectiveness based on parentage analysis

Introduction A hatchery-reared silver carp (Hypophthalmichthys molitrix) program has been intensively carried out since 2010 to enhance the rapidly declining fisheries production in the middle Yangtze River. However, only a little information regarding the effectiveness of the enhancement program has been reported. In this context, this study investigates on an enhancement program through monitoring the efficacy based on parentage analysis. Methods A total of 1,529 hatchery-reared fish and 869 larvae were sampled from the middle Yangtze River in 2016 and 2017 and were genotyped by thirteen microsatellite loci. Based on the results of parentage analysis the larvae were divided into three populations: (1) larvae population with both parents being hatchery-reared fish (=R), (2) larvae population with only a male or a female parent being hatchery-reared fish (=H), and (3) larvae population with no hatchery-reared fish parent (=W). The following analyses were also carried out: (1) assessing the contribution of hatchery-reared offspring to larval resources, and (2) evaluating the genetic effect of stock enhancement on the wild population. Results In total, 10.37% and 11.56% of larvae were identified as the offspring produced by hatchery-reared fish released in 2016 and 2017, respectively. In 2017, some of the larvae were assigned unambiguously to hatchery-reared fish released in 2016. In terms of the number of offspring produced, the hatchery-reared fish have shown significant variations. No significant differences were found among all the larvae populations concerning genetic parameters for diversity. High levels of genetic diversity of all larvae populations were obtained. Low FSTvalues obtained from pairwise FST analysis, as well as the analysis of molecular variance (AMOVA), revealed high genetic structural similarity among all the larvae populations. The genetic composition of the W larvae population in 2017 was different from that of all other larvae populations (all larvae populations in 2016, and R and H larvae populations in 2017), as demonstrated from the results of STRUCTURE and PCA analyses. Conclusion It was demonstrated that hatchery-reared fish are successful in producing the offspring in the natural environment during multiple years, which might assist in increasing the abundance of larvae. The hatchery-reared fish had variations in terms of the success rates on reproduction. Also, the hatchery-reared enhancement program had no significant effect on the genetic diversity or the genetic structure of wild populations. However, the genetic component of the W larvae population in 2017 was changed as compared to 2016, which was not due to the hatchery-reared enhancement program for silver carp. This could be due to flooding, but the specific causes need further studies. Our results clearly show the necessity to continuously inspect the genetic impact of the enhancement program so that historical information can be utilized for further research

Species diversity of drifting fish eggs in the Yangtze River using molecular identification

The dam constructions greatly changed the hydrologic conditions in the Yangtze River, and then significantly affected the spawning activities of indigenous river fish. Monitoring the species composition of drifting eggs during spawning season is important for protection issues. In this study, we have sampled drifting fish eggs in nine locations from 2014 to 2016. Eggs were identified using the mitochondrial cyt b gene sequence. A total of 7,933 fish eggs were sequenced successfully and blasted into the NCBI database. Thirty-nine fish species were identified, and were assigned to four families and two orders. Approximately 64% of the species identified, and 67% of the eggs, were classified in the Family Cyprinidae. Abundance and Shannon–Wiener diversity index of species were higher in the main river than in tributaries of the river. However, tributaries may be important spawning grounds for some fish species. The Jaccard’s similarity index and river-way distances among sampled stations were negatively correlated suggesting the environment shapes species composition in the sampled spawning grounds. These results showed that mitochondrial DNA sequence is a powerful and effective tool for fish egg identification in Yangtze River and these data are useful for conservation efforts

Role of Pirh2 in Mediating the Regulation of p53 and c-Myc

Ubiquitylation is fundamental for the regulation of the stability and function of p53 and c-Myc. The E3 ligase Pirh2 has been reported to polyubiquitylate p53 and to mediate its proteasomal degradation. Here, using Pirh2 deficient mice, we report that Pirh2 is important for the in vivo regulation of p53 stability in response to DNA damage. We also demonstrate that c-Myc is a novel interacting protein for Pirh2 and that Pirh2 mediates its polyubiquitylation and proteolysis. Pirh2 mutant mice display elevated levels of c-Myc and are predisposed for plasma cell hyperplasia and tumorigenesis. Consistent with the role p53 plays in suppressing c-Myc-induced oncogenesis, its deficiency exacerbates tumorigenesis of Pirh2−/− mice. We also report that low expression of human PIRH2 in lung, ovarian, and breast cancers correlates with decreased patients' survival. Collectively, our data reveal the in vivo roles of Pirh2 in the regulation of p53 and c-Myc stability and support its role as a tumor suppressor

Stable Isotope Analysis Reveals the Importance of Riparian Resources as Carbon Subsidies for Fish Species in the Daning River, a Tributary of the Three Gorges Reservoir, China

The patterns of carbon flow in large rivers influenced by dams are still not well known. We hypothesized that spatial variation in fish assimilation of basal production sources would be affected by heterogeneity of landscape-scale hydrology within a watershed due to the impoundment. We used stable isotope analysis and Bayesian mixing models to estimate relative contributions of basal production sources to fish consumers in a tributary of the Three Gorges Reservoir (TGR) with remarkably heterogeneous habitats between the upper and lower reaches. Model estimates indicated that riparian C3 plants were the main basal food source irrespective of reaches or feeding groups. Autochthonous algae carbon also appeared to be important as secondary carbon sources. However, the major contributive aquatic algae in the upstream were benthic algae while planktonic algae were important in the downstream, and this difference was related to their distinct hydrological characteristics. The contribution from C4 plants was comparatively less important to all fish consumers. Our results highlighted the significance of the riparian C3 carbon source to fish consumers in the TGR tributary and that the difference in landscape-scale characteristics was not enough to influence the pattern, which may be attributed to abundant standing stock of the riparian plants as well as hydrologic regimes in this river

Effects of Predation Stress on the Physiological Responses of Juvenile Four Major Chinese Carps

As low-level aquatic vertebrates, fish are highly dependent on the water environment, and general activities such as growth, foraging, and reproduction are easily affected by changes in the external environment. Changes in environmental factors can lead to different degrees of stress response in fish, and trigger a series of physiological changes, which then affect the stability of the organism's internal environment. Predation is one of the main environmental factors affecting the survival of individuals. In nature, almost all species face the risk of predation. Brief encounters with predators can reduce feeding and other health-related activities in prey fish and/or trigger primary and secondary stress responses, including the release of stress substances into the bloodstream. In predation stress, after initially sensing stress, fish initiate a stress response to overcome the stress and restore homeostasis. The degree of physiological stress depends primarily on the intensity and duration of the stress. If the appearance of predators is intermittent, then the physiological state of the prey fish returns to normal quickly, which allows the stress response to promote physiological changes in the prey fish to better adapt to the environment. However, repeated or persistent and unavoidable stress situations cause the normal physiological response mechanisms of prey fish to become compromised. Physiological stress may have long-term negative effects on the immune system, growth, or reproduction, and may reduce the adaptability and survivability of prey fish in the environment. Many studies have confirmed that predation stress can cause physiological stress in fish. Different species of fish and even different groups of the same species vary greatly in the degree of stress and stress mode. More species-specific studies are required to determine the effects of different levels of predation stress on physiological stress in fish.Black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molitrix), and bighead carp (Aristichthys nobilis) are known as the four major Chinese carps. As common fish species in Chinese inland watersheds, the four major Chinese carps are ecologically and economically valuable. Over the years, many reasons such as hydraulic construction, environmental pollution, and overfishing have led to sharp declines in wild populations. In addition, the prevalence of predators in natural waters also threaten population growth. It remains unclear how the juveniles of the four major Chinese carps adjust their physiological processes to cope with predation stress. We investigate the physiological and energy metabolism adaptations by black carp, grass carp, silver carp, and bighead carp to predatory stress. We selected the common local enemies of natural waters, the snakehead carp (Channa argus) and the southern catfish (Silurus meridionalis) as predators. The levels of serum cortisol and biochemical parameters in the juveniles of the four major Chinese carps under the stress of no-predation (control), low-predation (indirect stress) and high-predation (direct stress) over 0 d, 7 d, and 14 d were investigated. Changes in the biochemical parameters were analyzed. The effects of different predation stress levels on serum cortisol and biochemical parameters were also analyzed. The results showed: (1) under different levels of predation stress, the biochemical parameters and serum cortisol levels of juveniles of the four major Chinese carps varied to different degrees but the trends were consistent; (2) the serum cortisol levels of juveniles of the four major Chinese carps increased significantly with the degree of predation stress and the stress duration, and showed the following patterns: non-predation group < low predation group < high predation group, 0 d < 7 d < 14 d. (3) Among the biochemical parameters, serum total protein concentration and cholesterol concentration were relatively stable and did not vary significantly. Glucose concentration and alkaline phosphatase increased with predation stress, while triglyceride had a decreasing trend. The results showed that juveniles of the four major Chinese carps adjust their physiological responses to enhance their own survivability according to the predation risk. After the predation stress treatment, the juveniles of the four major Chinese carps all underwent a stress response. Compared with indirect predation, direct predation had a more significant effect on the physiological response of fish, and the degree of stress increased with the stress duration. Among the detection parameters, serum total protein and cholesterol may not be sensitive parameters for stress in fish under predation stress. The most significant changes were in cortisol and glucose and may compensate for the increased energy demand by the organism during stress. The adaptation of physiological stress and energy metabolism to predation stress in juveniles of the four major Chinese carps under predation stress conditions provides a theoretical basis for the stress responses of an organism to environmental changes, and can also provide a scientific reference for exploring the ecological interactions between predator and prey

Ecological Flow Assessment to Improve the Spawning Habitat for the Four Major Species of Carp of the Yangtze River: A Study on Habitat Suitability Based on Ultrasonic Telemetry

Four major species of Chinese carp, namely black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), are important economic freshwater fish varieties in China. They primarily inhabit and breed in the Yangtze River. Unfortunately, the construction and operation of the Gezhouba Dam and the Three Gorges Dam have dramatically changed the hydrodynamic conditions in the middle reaches of the Yangtze River, leading to a sharp decline in the reproduction rates of these carp. The egg abundance of the four species of carp downstream from the Three Gorges Dam reached 8.35 billion in 1965, but abundance during 2005&ndash;2012 was only 0.25 billion. One of the main reasons was that the hydrodynamic conditions of the spawning ground could not meet the four species&rsquo; breeding requirements. However, due to the limitations of traditional detection tools, the spawning characteristics of these four species of carp were still unclear. In this study, the ultrasonic telemetry and a three&ndash;dimensional hydrodynamic model were utilized to build the habitat suitability index (HSI) curves for the four species of carp. The habitat suitability model was then built based on HSI curves to assess spawning habitat quantity under different flow conditions. Finally, the habitat suitability model in the Yidu spawning ground was validated using 32 groups of sampling data in 2015 and 2017. The statistical results showed that the most suitable velocity ranged from 0.78 m/s to 0.93 m/s. The most suitable water depth ranged from 14.56 m to 16.35 m, and the most suitable Froude number ranged from 0.049 to 0.129. The habitat suitability model simulation results indicated that when the discharge was between 15,000 m3/s and 21,300 m3/s, the weighted usable area (WUA) values in both the Yidu and Zhicheng spawning grounds would remain at a high level. The validation results showed that most spawning activities occurred at a high level of WUA, and that the daily spawning egg numbers increased with the WUA value. Therefore, discharges of between 15,000 m3/s and 21,300 m3/s could be recommended as ecological operation target flows. We propose a feasible ecological operation scheme by setting the initial flow at 15,000 m3/s and maintaining the daily discharge increase at 1500 m3/s for 4 days

Comparative Analysis of Metabolites between Different Altitude <i>Schizothorax nukiangensis</i> (Cyprinidae, Schizothoracine) on the Qinghai-Tibet Plateau in Nujiang River

In order to investigate the influence of the high-altitude aquatic environment on indigenous fish metabolites, metabolomics studies were applied in this study. Widespread throughout the main stem of the Nujiang River of Schizothorax nukiangensis, we established sampling sites at high (3890 m) and low (2100 m) altitudes and selected six S. nukiangensis at each location, each weighing approximately 150 g and looking healthy. Then, metabolomics analysis was performed to compare the various metabolites of the two groups. Low concentrations of amino acids, dipeptides, eicosapentaenoic acid, docosahexaenoic acid, pentadecanoic acid, Thioetheramide-PC, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine, 1-Stearoyl-sn-glycerol-3-phosphocholine, 1-Myristoyl-sn-glycero-3-phosphocholine and 1-Palmitoyl-sn-glycero-3-phosphocholine, high concentrations in S-Methyl-5’-thioadenosine, creatine, D-mannose-6-phosphate, D-mannose-1-phosphate, oleic acid and myristoleic acid were found in high-altitude fish liver. These differentially accumulated metabolites were involved in oxidative stress, energy metabolism, carbohydrate metabolism and lipid metabolism. mTOR signaling pathway, apoptosis and lysosome were the KEGG pathways that were enriched between different groups to ensure energy supply and limit tissue damage of fish at high altitudes. All these results contributed to the understanding of the high-altitude adaptation of S. nukiangensis in the Nujiang River. Nicotine and methoprene, two organic pollutants, performed differently in fish at different altitudes. Overall, our findings advanced the fundamental understanding of fish responses to high-altitude environments, adaptive mechanisms and organic contaminants pollution in the Nujiang River

The complete mitochondrial genome of Pseudobagrus pratti and its phylogeny

Pseudobagrus pratti is a unique freshwater fish and mainly distributed in the Yangtze River and Pearl River systems. In this study, the complete mitochondrial genome of P. pratti was first determined. The total length of the complete mitochondrial genome is 16,533 bp, contained 13 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes, one D-loop locus, and an origin of replication on the light-strand (OL). The overall nucleotide composition was 31.55% A, 26.76% T, 26.78% C, 14.91% G, with 58.31% AT, respectively. Phylogenetic analysis both highly supported that P. pratti showed a close relationship with P. ussuriensis and P. emarginatus. These data would contribute to elucidate the evolutionary mechanisms and biogeography of Pseudobagrus and is useful for the conservation of genetics and stock evaluation for P. pratti

Relationship between the Distribution of Broodstock and Vorticity of Spawning Grounds of Four Major Chinese Carps in the Middle Reaches of the Yangtze River during Ecological Operation of the Three Gorges Dam

Hydrodynamic characteristics of spawning grounds are important factors affecting the spawning of four major Chinese carps (Mylopharyngodon piceus, Ctenopharyngodon idella, Hypophthalmichthys molitrix, and Aristichthys nobilis). To investigate the relationship between the preferred hydrodynamic characteristics of spawning sites and the response of fish spawning behavior, we monitored the flow field of spawning sites during ecological operation of the Three Gorges Dam (i.e., man-made flood regulation) in 2014 and 2015. We used the data to explore the correlation between vorticity changes in spawning grounds and the spawning amount. Pearson correlation coefficients of the average vorticity in all cross-sections of the Yidu spawning ground and spawning amount in 2014 and 2015 were 0.730 and 0.822, respectively, indicating a significant positive correlation between vorticity and spawning activity. In some specific regions, this correlation was even stronger (Pearson correlations of the regional vorticity and egg production were &gt;0.95). To further corroborate and analyze the relationship between these specific regions and the distribution of broodstock during the breeding season, an ultrasonic telemetry test of broodstock was conducted in the Yidu spawning ground in 2016. The results showed that the broodstocks were concentrated in the reach near the Quantong Pier (~76 km from the Three Gorges Dam). These regions were consistent with areas of river characterized by highly correlated vorticity and egg production levels, suggesting that these regions are areas preferred by four major Chinese carps for spawning

Monitoring the genetic effects of broodstock enhancement of silver carp (Hypophthalmichthys molitrix) in middle Yangtze River based on cytb gene and D-loop sequences

In this study, we first evaluated the genetic effects of the stock enhancement program of silver carp (Hypophthalmichthys molitrix) on wild populations in the middle Yangtze River using the sequences of the mitochondrial Cytochrome b gene and control region (D-loop). 129 cytb individuals and 135 D-loop individuals were sequenced successfully, and the results obtained by two markers were similar. T test results showed that there was no significant difference in haplotype diversity (Hd) values and nucleotide diversity (Pi) values before and after release. The exact test result of population differentiation based on haplotype frequencies was consistent with no significant change in haplotype frequency after release. Pairwise genetic differentiation index (FST) and gene flow (Nm) revealed no genetic differentiation among four populations. Results of the Bayesian clustering analysis performed with STRUCTURE and analysis of molecular variance (AMOVA) confirmed that the genetic component did not change after release. In summary, there was no significant genetic effect of broodstock enhancement of silver carp on wild populations in the middle Yangtze River