Dissecting the chromosome-level genome of the Asian Clam (Corbicula fluminea)

The Asian Clam (Corbicula fluminea) is a valuable commercial and medicinal bivalve, which is widely distributed in East and Southeast Asia. As a natural nutrient source, the clam is rich in protein, amino acids, and microelements. The genome of C. fluminea has not yet been characterized; therefore, genome-assisted breeding and improvements cannot yet be implemented. In this work, we present a de novo chromosome-scale genome assembly of C. fluminea using PacBio and Hi-C sequencing technologies. The assembled genome comprised 4728 contigs, with a contig N50 of 521.06 Kb, and 1,215 scaffolds with a scaffold N50 of 70.62 Mb. More than 1.51 Gb (99.17%) of genomic sequences were anchored to 18 chromosomes, of which 1.40 Gb (92.81%) of genomic sequences were ordered and oriented. The genome contains 38,841 coding genes, 32,591 (83.91%) of which were annotated in at least one functional database. Compared with related species, C. fluminea had 851 expanded gene families and 191 contracted gene families. The phylogenetic tree showed that C. fluminea diverged from Ruditapes philippinarum, ~ 228.89 million years ago (Mya), and the genomes of C. fluminea and R. philippinarum shared 244 syntenic blocks. Additionally, we identified 2 MITF members and 99 NLRP members in C. fluminea genome. The high-quality and chromosomal Asian Clam genome will be a valuable resource for a range of development and breeding studies of C. fluminea in future research.

Antibiogram of Escherichia coli isolated from semi-closed system farmed Asian clam (Corbicula fluminea)

In the present study, antibiogram of Escherichia coli isolated from farmed Asian clam, Corbiculafluminea was characterised. Asian clam or locally known as ‘etak’ is processed to became smokedclam and consumed as snack by Kelantanese. However, there are many diarrhoea cases afterconsuming smoked clam. Furthermore, there are also insufficient information about the E.coli levelin Asian clam farm and effective antibiotic in controlling the bacteria in the litereature. Hence, thisstudy was carried out to provide information of antibiogram of E.coli to be reference in the future.Eosin Methylene Blue agar (EMB) was used to isolate E. coli. A total of 100 isolated bacteria weresubjected to antibiotic sensitivity test using disk diffusion method. A total of 18 types of antibioticsnamely novobiocin (30µg/disk), fosfomycin (50 µg/disk), tetracycline (30µg/disk), lincomycin(15µg/disk), flumequine (30µg/disk), sulphamethoxazole (25 µg/disk), amoxycillin (25 µg/disk),chloramphenicol (30 µg/disk), oleandomycin (15 µg/disk), spiramycin (100 µg/disk), ampicillin(10 µg/disk), oxytetracycline (30 µg/disk), doxycycline (30 µg/disk), nalidixic acid (30 µg/disk),florfenicol (30 µg/disk), erythromycin (15 µg/disk), kanamycin (30 µg/disk) and oxolinic acid (2µg/disk). The findings of the present study showed total plate count of E. coli was 6.45 x 103 colonyforming unit (CFU/100g) of sampled Asian clam. Hence, the clam is needed to be under cleansingtreatment before can consider safe for human consumption. Antibiotic results showed 51 % wasrecorded as antibiotic resistance case, 44 % antibiotic sensitive case and 5 % as antibioticintermediary sensitive case. None of the tested antibiotics was successfully inhibited the growth ofthe present bacterial isolates indicating more antibiotics are needed to be screen in the future studyto find out the most effective antibiotic in controlling isolated E. coli.

Effects of Feeding Treatments on Growth and Survival of Asian Clam (Corbicula fluminea) in the Hatchery

Asian clam (Corbicula fluminea) is potentially reared as aquaculture species but feeding regimes and nutrition for this clam remain questioned. The growth and survival of C. fluminea were evaluated with the assessment of feeding regimes raised in captive rearing treatments (with substrates) fed with spirulina (Arthrospira platensis). Three feeding methods were applied, Treatment A: deposit-feeding, Treatment B: suspension feeding, and Treatment C: combination deposit and suspension-feeding. Shell length (SL) and weight of the individuals were taken every 7 d which last for 6 wk. Condition index (CI), instantaneous growth rates of weight (Kw), and SL (KL) were determined after the experiment ends. Water parameters such as temperature (°C), pH, ammonia (NH4), and dissolved oxygen (DO) also being monitored along the experimental period. Significant weight gained (Kw) and CI was found higher in C. fluminea fed in Treatment C, where the increment was recorded at 6.24x10-3±2.4x10-3gday-1 and 4.34 ±0.3 respectively. Whereas, the increment of SL (KL) was insignificant in all treatments. Survival rates (SR) were greater than 95% in all treatments. The rearing conditions are significant factors that affect the feed utilization for their growth. The growth and survival indicate the specific feeding methods for captive C. fluminea and spirulina feasibility as their feed.

Cold tolerance varies among invasive populations of the Asian clam Corbicula fluminea

The distribution of the subtropical Asian clam Corbicula fluminea (Müller, 1774), one of the world’s most invasive freshwater molluscs, is reportedly constrained by a lower thermal tolerance limit of 2°C. Although its occurrence in north temperate regions is typically restricted to artificially heated waterbodies, the species has been found to overwinter in unheated lakes and rivers. In laboratory experiments, we compared the cold tolerance of populations from several geographically distinct sites spanning 35°N to 46°N in eastern North America. Each population contained individuals that fully recovered from two months of continuous exposure to near freezing (1°C) conditions, contrary to published accounts of C. fluminea’s thermal ecology. Survivorship increased with body size and was enhanced by prior acclimation to a low temperature (10°C) compared to a higher one (18°C). When acclimated to 10°C, clams from northern populations exhibited greater survivorship (55.0 ± 16.1%) than those from southern populations (26.7 ± 19.2%). However, one southern population demonstrated survivorship as great as that of the most tolerant northern population, suggesting that its clams could overwinter in unheated northern waterbodies. Differences among populations indicate either that contemporary evolution has occurred or that developmental plasticity shapes future acclimation responses.

Smoke on the Water: Comparative Assessment of Combined Thermal Shock Treatments for Control of Invasive Asian Clam, Corbicula fluminea

Suppression of established populations of invasive alien species can be a complex and expensive process, which is frequently unsuccessful. The Asian clam, Corbicula fluminea (Müller, 1774), is considered a high impact invader that can adversely alter freshwater ecosystems and decrease their socioeconomic value. To date, C. fluminea continues to spread and persist within freshwater environments worldwide, despite repeated management attempts to prevent dispersal and suppress established populations. As extensive C. fluminea beds can often become exposed during low-water conditions, the direct application of hot or cold thermal shock treatments has been proposed as suitable mechanism for their control. Further, mechanical substrate disturbance may enhance the efficacy of thermal shock treatments by facilitating exposures to multiple layers of buried clams. In the present study, we advanced these methods by assessing combined applications of both hot and cold thermal shock treatments for control of C. fluminea, using steam spray (≥100 °C; 350 kPa), low- or high-intensity open-flame burns (~1000 °C) and dry ice (−78 °C). In a direct comparison of raking combined with hot thermal shock applications, both steam and high-intensity open-flame treatments tended to be most effective, especially following multiple applications. In addition, when hot thermal treatments are followed by a final cold shock (i.e. dry ice), steam treatments tended to be most effective. Further, when dry ice was applied either alone or prior to an application of a hot shock treatment, substantial if not complete C. fluminea mortality was observed. Overall, this study demonstrated that combined applications of hot and cold thermal shock treatments, applied following the disruption of the substrate, can substantially increase C. fluminea mortality compared to separate hot or cold treatments.

Dissecting the Chromosome-Level Genome of The Asian Clam (Corbicula Fluminea)

The Asian Clam (Corbicula fluminea) is a valuable commercial and medicinal bivalve, which is widely distributed in East and Southeast Asia. As a natural nutrient source, the clam is high in protein, amino acids, and microelements. The genome of C. fluminea has not yet been characterized; therefore, genome-assisted breeding and improvements cannot yet be implemented. In this work, we present a de novo chromosome-scale genome assembly of C. fluminea using PacBio and Hi-C sequencing technologies. The assembled genome comprised 4,728 contigs, with a contig N50 of 521.06 Kb, and 1,215 scaffolds with a scaffold N50 of 70.62 Mb. More than 1.51Gb (99.17%) of genomic sequences were anchored to 18 chromosomes, of which 1.40 Gb (92.81%) of genomic sequences were ordered and oriented. The genome contains 38,841 coding genes, 32,591 (83.91%) of which were annotated in at least one functional database. Compared with related species, C. fluminea had 851 expanded gene families and 191 contracted gene families. The phylogenetic tree showed that C. fluminea diverged from Ruditapes philippinarum, ~ 228.89 million years ago (Mya), and the genomes of C. fluminea and R. philippinarum shared 244 syntenic blocks. Additionally, we identified 2 MITF members and 99 NLRP members in C. fluminea genome. The high-quality and chromosomal Asian Clam genome will be a valuable resource for a range of development and breeding studies of C. fluminea in future research.