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The red swamp crayfish, Procambarus clarkii (Girard, 1852), is currently an economically important aquaculture animal. Its genetic basis has been scarcely reported, however, partly due to the absence of abundant molecular markers in the genome. In this study, Simple Sequence Repeat (SSR) loci were mined, based on genome survey sequencing via the next generation sequence of the red swamp crayfish. A total of 4897 SSR loci were identified, with the most abundant type being the di-nucleotide repeat motifs (75.2%), followed by tri- (20.4%), tetra- (3.8%), penta- (0.5%), and hexanucleotide (0.2%) repeats. In total, 1546 SSR markers were validated to be amplified, and 721 of these were identified as polymorphic SSR markers. Fifty polymorphic SSR markers were randomly selected for the identification of the genetic diversity of the 14 red swamp crayfish populations in China. The expected and observed heterozygosity and polymorphism information content were 0.39, 0.30, and 0.29, respectively, on average. The results indicated a medium genetic diversity among the 14 investigated populations. These probably cluster into three genetic populations. The current study provides abundant genetic markers and information on the 14 populations, which can be helpful for genetic diversity estimation and molecular breeding of the red swamp crayfish. Résumé: L'écrevisse rouge de Louisiane, Procambarus clarkii (Girard, 1852), est une espèce d'aquaculture importante économiquement. Sa base génétique est peu connue, due en partie à l'absence de marqueurs moléculaires abondants dans son génome. Dans cette étude, l'analyse des microsatellites (SSR) de l'écrevisse rouge a été effectuée, sur la base d'un séquençage du génome par séquençage nouvelle génération (NGS). Un total de 4897 loci SSR ont été identifiés, le type le plus abondant de motifs répétés étant les di-nucléotides (75,2%), suivi par les répétitions à tri- (20,4%), tétra- (3,8%), penta- (0,5%), et hexa-nucléotides (0,2%). Au total, 1546 marqueurs ont été validés pour être amplifiés, et 721 d'entre eux ont été identifiés comme marqueurs SSR polymorphiques. 50 marqueurs SSR polymorphiques ont été sélectionnés au hasard pour l'identification de la diversité génétique des 14 populations d'écrevisse rouge de Louisiane en Chine. L'hétérozygotie attendue et observée et l'indice de polymorphisme ont été, en moyenne, respectivement de 0,39, 0,30, et 0,29. Les résultats montrent une diversité génétique moyenne parmi les 14 populations étudiées, qui se regroupent probablement dans trois populations génétiques. Cette étude fournit des marqueurs génétiques abondants et des informations sur les 14 populations, qui peuvent être utiles pour l'estimation de la diversité génétique et la sélection moléculaire de l'écrevisse rouge de Louisiane. [ABSTRACT FROM AUTHOR]

• Accumulation of Mn, Fe, Cu, Zn and Se in crayfish of China was assessed. • Concentrations of the five elements in muscle were lower than those in hepatopancreas. • Se is highly enriched in the investigated crayfish, carp and crab. • Humans can obtain sufficient Se by consuming crayfish, carp and crab. The red swamp crayfish is an important aquatic food for humans. In this study, the accumulation of trace elements, such as manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), and selenium (Se) in the hepatopancreas, abdominal muscle, and exoskeleton of red swamp crayfish from four regions in China were investigated. The mean concentrations of Mn (21.01 mg/kg) and Fe (34.85 mg/kg) in the abdominal muscle were remarkably lower than those in the hepatopancreas (236.07 mg/kg and 2517.94 mg/kg) and exoskeleton (274.67 mg/kg and 111.34 mg/kg). The mean concentrations of Cu (19.62 mg/kg), Zn (73.95 mg/kg), and Se (1.04 mg/kg) in the abdominal muscle were remarkably higher than those (16.52 mg/kg, 21.79 mg/kg, 0.38 mg/kg) in the exoskeleton and lower than those (116.85 mg/kg, 124.74 mg/kg, 2.56 mg/kg) in the hepatopancreas, respectively. The concentrations of Cu (23.56 mg/kg) and Se (1.12 mg/kg) in the abdominal muscle of crayfish from the Ensi region were higher those in the other three regions. There was a highly significant positive correlation between the concentrations of Cu and Se in crayfish and those in the environment (r ≥ 0.68, P < 0.01). In addition, Se could be specifically enriched in the red swamp crayfish, and a similar situation was found in bighead carp and Chinese mitten crabs. These results highlight the level of intake of essential elements by humans. Importantly, the consumption of the abdominal muscles of crayfish does not result in the overdose of the five essential elements. Therefore, these findings provide new insights into food nutrition and safety control for the consumption of crayfish and other freshwater animals. [ABSTRACT FROM AUTHOR]

The food safety of a popular aquatic product, red swamp crayfish (Procambarus clarkii), has caused widespread public concern. Rice-crayfish mixed farming currently takes advantage of crayfish production and is becoming the dominant farming method. It is still unknown whether this new aquaculture model produces crayfish with safe accumulated doses of toxic heavy metals and metalloids. In the current study, eleven farms in the Hubei and Hunan provinces, which account for more than 60% of the crayfish production in China, were selected to sample crayfish and their culture environment background (sediment and water), and determine their As, Cr, Cd, and Pb levels. The estimated daily intake (EDI) risk model was used to evaluate the human health risk of consuming crayfish. The concentrations of the four toxic elements were lower in the abdominal muscle than in the exoskeleton and hepatopancreas that is not suggested to be consumed. As the edible part, abdominal muscle did not exceed the national safety threshold for toxic elements. The geographic environmental background had little impact on the accumulation of toxic elements in the abdominal muscle of crayfish. The EDI results suggest that neither children nor adults exceed the provisional tolerable daily intake threshold, and the target hazard quotient (THQ) and cancer health risk (CR) for both children and adults were less than 0.12 and 1.5 × 10−9, respectively, which are far less than the thresholds (THQ < 1 and CR < 10−6). Furthermore, 139 and 488 kg crayfish were the critical values for the annual consumption by children (20 kg) and adults (70 kg), respectively. • It is not suggested to consume hepatopancreas of crayfish for human. • Arsenic accumulates more than Cd, Cr, and Pb in the abdominal muscle of crayfish. • There is a low or no health risk for consumption of abdominal muscle of crayfish. • The critical value of crayfish consumption by children (20 kg) is 139 kg/year. • The critical value of crayfish consumption by adults (70 kg) is 488 kg/year. [ABSTRACT FROM AUTHOR]