A Significant Genetic Admixture in Farmed Populations of the Noble Scallop Chlamys nobilis Revealed by Microsatellite DNA Analysis in Southern China

The noble scallop, Chlamys nobilis, is an important bivalve mollusk with high commercial value and is usually farmed in the waters of southern China. To date, very little is known about the genetic diversity and population structure of C. nobilis. In this study, 10 microsatellite loci of four farmed C. nobilis populations were compared with one another and compared wild population in southern China. A total of 83 alleles were found. Surprisingly, the level of genetic diversity of the farmed C. nobilis populations was higher than that of the wild population. Although the population genetic of wild population was completely in the Hardy–Weinberg equilibrium, due to heterozygote deficiency, significant deviations from the Hardy–Weinberg equilibrium were found in all farmed populations, suggesting a genetic admixture caused by the mixing of seeds from various hatcheries. The Fst and AMOVA values showed significant genetic differences between wild and farmed populations. The Bayesian assignment also confirmed that genetic admixture was significant and widespread in artificial breeding of C. nobilis. Furthermore, the UPGMA tree topology and PCA demonstrated that the genetic diversity of wild population can be clearly distinguished from farmed populations. In a nutshell, the findings of this study not only fill the knowledge gaps in genetic diversity of wild and farmed C. nobilis populations, but also serve as a guide for maintaining the genetic diversity of C. nobilis in both farmed and wild populations.

Dietary Exposure Assessment of Paralytic Shellfish Toxins through Shellfish Consumption in Shenzhen Population, China

Paralytic shellfish toxins (PSTs) produced by certain marine dinoflagellates accumulate in filter-feeding marine bivalves. We used LC-MS/MS to detect and quantify 13 PSTs in 188 shellfish samples of 14 species collected from Shenzhen city’s Buji seafood wholesale market from March 2019 to February 2020. Twenty-six of 188 shellfish samples (13.8%) were PST- positive, with highest values in samples of the Noble clam Chlamys nobilis (10/34, 29.4%). Samples originating from Nan’ao island among 11 source sites in China recorded the highest detected rate (7/17, 41.2%). Samples containing PSTs were concentrated in Spring and Winter, with the highest levels in March > December > January. Among PSTs detected, C1 was dominant. Acute dietary exposure assessments for Shenzhen residents were based on P99 consumption data (139.2g/day) and maximum PST concentration for each shellfish species. The outcome for Chlamys nobilis was 2.4 ~ 3.7-fold higher than recommended ARfDs (0.5 ~ 0.7 µg STX eq./kg bw/day). Mean PST concentration (10.9 ~ 134.1 µg STX Eq. /kg), mean shellfish consumption (4.8 g/day) and P99 consumption data were used to assess chronic dietary exposure. The results were lower than the recommended ARfDs. In conclusion, residents in Shenzhen are at risk for acute PST poisoning, while relatively safe from chronic PST exposure.