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Portunus trituberculatus is an important economic species of crab that is artificially bred and released in the Yangtze River Estuary and its adjacent sea areas. Based on six microsatellite markers, we investigate the genetic diversity and structure of 101 P. trituberculatus specimens collected from two hatcheries in Nantong and Zhoushan that participated in stock enhancement in the year 2019. We compared these with 124 wild specimens caught from 13 localities in the estuary. Analysis of several genetic diversity parameters (NA, RS, I, HO, HE, FIS, and FST) for the 15 populations demonstrates that both released and wild populations possess relatively rich genetic diversity. Furthermore, the released groups demonstrate no less genetic variation between themselves than do the wild crabs. Most FIS values are greater than zero, which shows inbreeding is common among specimens with geographically open sites. However, insufficient sampling may have led to a wide distribution of null alleles, a Hardy–Weinberg test disequilibrium in microsatellite markers PN22 and P04, and a lack of crab genetic diversity in site 14. All populations (except locality 14) have not suffered the bottleneck effect. Four subgroups can be seen to roughly spread longitudinally along the sample area by performing pairwise comparisons of genetic distance and FST values among the populations. No obvious topological heterogeneity is discovered among the four subgroups in a phylogenetic tree. The existence of genetic exchange and differentiation among the subgroups is also verified using structure analysis. Therefore, based on this evidence, we propose that the hatchery stock enhancements performed in Nantong and Zhoushan result in no reduction in genetic diversity for wild populations in the Yangtze Estuary in 2019. [ABSTRACT FROM AUTHOR]

Portunus trituberculatus is an important invertebrate species distributed in the Yangtze Estuary. However, its biomass and enrichment have been affected seriously by ongoing human activity in recent decades. The length-based Bayesian biomass estimator (LBB) is a novel and potent method to estimate the stocks for most commercial fishes and invertebrates in offshore using only length and frequency data. In this study, the results showed that the ratio of current exploited biomass relative to unexploited biomass (B/B0) was smaller than relative biomass capable of producing maximum sustainable yields (BMSY/B0) after handling of the catches of the P. trituberculatus collected from the Yangtze Estuary in 2018 using the LBB method. Therefore, this evidence indicated that the biomass of the swimming crab was relatively low as a result of the overfishing in this water area and the catches of the crabs should be controlled at a reasonable level in the future. Meanwhile, LBB is a promising method providing a theoretical basis for the management and protection of fishery resources. [ABSTRACT FROM AUTHOR]

Surveys and assessments based on environmental DNA are not only efficient and time-saving, but also cause less harm to monitoring targets. Environmental DNA has become a common tool for the assessment and monitoring of aquatic organisms. In this study, we investigated fish resources in the Yangtze River mainstream using environmental DNA, and the variations in fish during two seasons (spring and autumn) were compared. The results showed that 13 species were identified in spring, and nine species of fish were identified in autumn. The fish with higher eDNA detection were Sinibotia superciliaris, Tachysurus fulvidraco, Cyprinus carpio, Ctenopharyngodon Idella, Monopterus albus, Acanthogobius hasta, Saurogobio dabryi, Oncorhynchus mykiss, Mugil cephalus, Odontamblyopus rubicundus. Seasonal variation between spring and autumn was not significant, and the environmental factors had different effects on fish assemblages during the two seasons. Our study used the eDNA technique to monitor the composition of fish in the spring and autumn in the Yangtze River mainstream, providing a new technology for the long-term management and protection of fishery resources in the region. Of course, problems such as pollution and insufficient databases are the current shortcomings of environmental DNA, which will be the focus of our future research and study. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome ofAnguilla japonicacollected from Yangtze estuary was determined by next-generation sequencing. The mitogenome is a circular molecule 16 715 bp in length, including the typical structure of 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and a control region. The TAS, central CSB and CSB were detected in the control region. The gene contents of the mitogenome are identical to those observed in most bony fishes. The phylogenetic tree in the genusAnguillashowed thatA. japonicaclustered in a separate branch. [ABSTRACT FROM AUTHOR]