Background: The Chinese grass shrimp,Palaemonetes sinensis, is an economically important freshwater shrimp in China, and the study of genetic diversity and structure can positively contribute to the exploration of germplasm resources and assist in the understanding ofP. sinensisaquaculture. Microsatellite markers are widely used in research of genetic backgrounds since it is considered an important molecular marker for the analyses of genetic diversity and structure. Hence, the aim of this study was to evaluate the genetic diversity and structure of wildP. sinensispopulations in China using the polymorphic microsatellite makers from the transcriptome.Results: Sixteen polymorphic microsatellite markers were developed forP. sinensisfrom transcriptome, and analyzed for differences in genetic diversity and structure in multiple wildP. sinensispopulations in China. Totally of 319 individual shrimps from seven different populations were genotyped to find that allelic polymorphisms varied in two to thirteen alleles seen in the entire loci. Compared to other populations analyzed, the two populations including LD and SJ showed lower genetic diversity. Both the genetic distance (D) and Wrights fixation index (F_ST) comparing any two populations also indicated that LD and SJ populations differed from the other five populations. An UPGMA tree analysis showed three main clusters containing SJ, LD and other populations which were also confirmed using STRUCTURE analysis.Conclusion: This is the first study where polymorphic microsatellite markers from the transcriptome were used to analyze genetic diversity and structures of different wildP. sinensispopulations. All the polymorphic microsatellite makers are believed useful for evaluating the extent of the genetic diversity and population structure ofP. sinensis. Compared to the other five populations, the LD and SJ populations exhibited lower genetic diversity, and the genetic structure was differed from the other five populations. Therefore, they needed to be protected against further declines in genetic diversity. The other five populations, LP, LA, LSL, LSY and LSH, are all belonging to Liaohe River Drainage with a relatively high genetic diversity, and hence can be considered as hot spots for in-situ conservation ofP. sinensisas well as sources of desirable alleles for breeding values.

Although co-culture of paddy fields with aquatic animals is lucrative, the ecological impacts of high-protein content entering the agricultural soil via animal pellet feed and feces have not been well studied. Moreover, the effects of dietary protein on soils and soil microbes remain unclear. To elucidate this, we examined soil bacterial and fungal community composition and temporal changes in paddy fields subjected to different protein-content diets via 16S/18S rRNA gene amplicon sequencing analysis with a high-throughput next-generation sequencer. MiSeq sequencing revealed that protein content significantly impacted fungal community structure. High-protein diets reduced bacterial community diversity and relative abundance in both July and October. The phylum-level bacterial taxonomic composition was not affected by diet treatment, while in fungi, a major phylum-level shift was evident. Hierarchically clustered analysis showed that high-protein diets significantly reduced the relative abundance of Brevundimonas in both July and October. Saprotrophic macrofungal diversity was negatively related to dietary protein content. Considering microbial community structure and environmental factors, ca. 15% protein content is appropriate for the rice-crab co-culture system that we studied.

The Chinese mitten crab, Eriocheirsinensis, is an important farmed crustacean species in China, outranking other farmed crabs in yield and economic importance. An infection called “milky disease”, caused by the yeast, Metschnikowiabicuspidata, has emerged in E. sinensis farms in northeast China and has caused progressive economic losses. The diseased crabs present with opaque, whitish muscles and milky hemolymph. Currently, there are no effective drugs to treat the infection. Clarifying the transmission route of M. bicuspidata would help to treat and prevent the disease. We investigated the effects of three different M. bicuspidata infection methods (feeding, immersion, and cohabitation) on E. sinensis. All three infection methods led to a high infection rate in healthy crabs. After 35 d, the infection rate was 76.7%, 66.7%, and 53.3% in the feeding, immersion, and cohabitation groups, respectively. Diseased crabs exhibited the typical symptom of hemolymph emulsification, with a high pathogen load of M. bicuspidata. The yeast was not detected in the oocytes of infected crabs. Fertilized embryos, zoea larvae, and megalopae of infected ovigerous crabs tested negative for yeast, indicating that direct transmission from mother to offspring does not occur. Our results highlight avenues for the prevention and control of this yeast.

Background: Chinese grass shrimp (Palaemonetes sinensis) is an important species widely distributed throughout China, which is ecologically relevant and possesses ornamental and economic value. These organisms have experienced a sharp decline in population due to overfishing. Therefore interest inP. sinensisaquaculture has risen in an effort to alleviate fishing pressure on wild populations. Therefore, we investigated the genetic diversity and variation ofP. sinensisto verify the accuracy of previous research results, as well as to assess the risk of diversity decline in wild populations and provide data for artificial breeding.Methods: Palaemonetes sinensisspecimens from seven locations were collected and their genetic variability was assessed based on mitochondrialCOIgene segments. DNA sequence polymorphisms for each population were estimated using DNASP 6.12. The demographic history and genetic variation were evaluated using Arlequin 3.11. At last, the pairwise genetic distance (Ds) values and dendrograms were constructed with the MEGA 11 software package.Results: Our study obtained sequences from 325 individuals, and 41 haplotypes were identified among the populations. The haplotype diversity (H_d) and nucleotide diversity (π) indices ranged from 0.244 ± 0.083 to 0.790 ± 0.048 and from 0.0004 ± 0.0001 to 0.0028 ± 0.0006, respectively. Haplotype network analyses identified haplotype Hap_1 as a potential maternal ancestral haplotype for the studied populations. AMOVA results indicated that genetic variations mainly occurred within populations (73.07%). Moreover, according to the maximum variation among groups (F_CT), analysis of molecular variance using the optimal two-group scheme indicated that the maximum variation occurred among groups (53.36%). Neutrality and mismatch distribution tests suggested thatP. sinensisunderwent a recent population expansion. Consistent with the SAMOVA analysis and haplotype network analyses, theDs andF_STbetween the population pairs indicated that the JN population was distinctive from the others.Conclusions: Our study conducted a comprehensive characterization of seven wildP. sinensispopulations, and our findings elucidated highly significant differences within populations. The JN population was differentiated from the other six populations, as a result of long-term geographical separation. Overall, the present study provided a valuable basis for the management of genetic resources and a better understanding of the ecology and evolution of this species.