Lua Thi Dang

Intertidal clam productivity is shaped by interacting water-column, sediment and biological conditions, but these components are usually assessed separately. Integrated assessment is therefore needed to identify habitat signals related to production and size-independent meat condition. Water quality, sediment properties, plankton, benthic fauna, clam density and clam performance were monitored at two Meretrix lyrata farming grounds during eight sampling periods in 2025. Size-standardized meat indicators were derived from shell–meat allometric residuals, and habitat–response relationships were examined using pooled and adjusted Spearman correlations, principal component analysis and exploratory integrated models. Total suspended solids (TSS) and water sulfide were the strongest negative indicators, correlating with fresh meat, dry meat, shell length and condition index (CI) (r=-0.64 to -0.69); TSS was also negatively related to size-standardized meat condition and the proportion of clams reaching ≥15 g (r=-0.41 to -0.47). Sediment total nitrogen and silt were negatively associated with clam responses, whereas sand showed positive associations with raw and size-standardized endpoints (r=0.44 - 0.60). After adjustment for station and month, water-quality indicators contributed 55.2% of the indicator-explained variation in raw production responses, whereas biological indicators contributed 59.1% of that in size-standardized meat condition; TSS (22.3%) and clam density (35.0%) ranked highest for the two response groups, respectively. These findings show that raw production traits and size-standardized meat residuals capture complementary dimensions of clam performance. Monitoring should prioritize TSS, water sulfide, sediment total nitrogen, sand–silt composition and clam density.

Fisheries and Aquatic Sciences

This is the first study to examine the effect of three different cultivation methods (bottom-tray culture, suspended-tray culture, and beach/bottom culture) on the growth and survival rates of the snout otter clam, Lutraria philippinarum, after 12 months of grow-out cultivation from seed to commercial size. Analyses included weight, survival, shell size, and total fat. Although the results showed limited differences in growth among cultivation methods, survival rates were significantly different among three different culture methods. The bottom-tray cultivation method had the highest survival rate (76.5%), compared with suspended-tray cultivation (31.6%) and beach/bottom cultivation (52.5%). This demonstrates that the most suitable method for commercial snout otter clam farming is cultivation trays placed on the bottom of the substrate. Improving commercial farming of the species will support the development and expansion of aquaculture in Vietnam and elsewhere, while reducing the harvest pressure on wild populations.

The integrated agriculture-aquaculture (IAA) farming system has been considered a form of diversified agriculture applied in Asia. In this paper, several IAA farming systems practiced in Vietnam are described, and their impacts are also reviewed. It is speculated that in developing countries like Vietnam, the IAA farming system should be targeted for support as a sustainable food safety model and a form of ecosystem-based technology to reduce environmental impacts, adapt to climate change, help avoid risks from market fluctuation, and increase incomes in comparison with monoculture farming.

The study aims to evaluate the infection prevalence, virulence gene distribution and antimicrobial resistance of Aeromonas hydrophila associated in diseased outbreaks of cultured freshwater fish in Northern Vietnam. The confirmed A. hydrophila were screened for the presence of the five pitutative-virulence genes including aerolysin (aerA), hemolysin (hlyA), cytotonic enterotoxin (act), heat-labile cytotonic enterotoxin (alt), and heat-stable enterotoxin (ast), and examined the susceptibility to 16 antibiotics. A total of 236 A. hydrophila isolates were recovered and confirmed from 506 diseased fish by phenotypic tests, PCR assays, and gyrB, rpoB sequenced analyses, corresponding to the infection prevalence at 46.4%. A total of 88.9% of A. hydrophila isolates harbored at least one of the tested virulence genes. The genes aerA and act were most frequently found (80.5% and 80.1%, respectively) while the ast gene was absent in all isolates. The resistance to oxacillin, amoxicillin and vancomycin exhibited the highest frequencies (>70%), followed by erythromycin, oxytetracycline, florfenicol, and sulfamethoxazole/trimethoprim (9.3–47.2%). The multiple antibiotic resistance (MAR) index ranged between 0.13–0.88 with 74.7% of the isolates having MAR values higher than 0.2. The results present a warning for aquaculture farmers and managers in preventing the spread of A. hydrophila and minimizing antibiotic resistance of this pathogen in fish farming systems.

This study focussed on the use and knowledge of antibiotics of tilapia and traditional freshwater species fish farmers in Hai Duong province, the major freshwater fish producing area in Red River Delta, Vietnam. As found from this cross‐sectional survey, antibiotics were used by 91.7% of a total 60 surveyed farmers for the purposes of disease prevention and treatment. However, 98.2% of these farmers carried out no form of antibiotic susceptibility testing before choosing, buying and using antibiotics. Additionally, 78.9% of the respondent farmers who experienced significant mortalities in their stocks immediately treated with antibiotics without any diagnostic analysis or support. Within those surveyed, whilst 76.7% believed that antibiotics could be used to treat bacterial diseases, 13.3% farmers thought that antibiotics could also be used to treat viral diseases. The use of antibiotics by surveyed farmers can be influenced by unreliable sources of information, such as sometimes given by drug manufacturers and sellers. Several antibiotics listed as ‘critically important’ in human medicine, along with antibiotics prohibited by the government, were used by surveyed farmers. Findings from this study indicate that government, academia and private sectors should work collaboratively together to improve consultative services, provide training on disease diagnosis, promote responsible use of antibiotics and develop alternative solutions/treatments replacing antibiotics. The authorities concerned should look to other national country models for monitoring and regulation of antibiotics use in aquaculture and identify constituent parts which can be appropriate, relevant and implementable in the context of Vietnamese aquaculture.

Objectives: The objectives are aimed to investigate the antibacterial properties of five Vietnamese medicinal plants against acute hepatopancreatic necrosis disease (AHPND)-caused bacterial pathogens, to verify their potentials to apply as a new treatment therapy.Methods: Extracts from plants, such as Psidium guajava leaf, Piper betle L. leaf, Phyllanthus amarus leaf, Rhodomyrtus tomentosa seed, and Allium sativum bulb, were tested against three AHPND-caused bacteria. Agar infusion and broth dilution methods were employed to evaluate extract in vitro antibacterial effects, while experiments with cultured whiteleg shrimps were applied to access their safety when applied in vivo. High-performance liquid chromatography (HPLC) analysis was applied to identify components in the extracts.Results: P. amanus and R. tomentosa extracts exerted the strongest inhibition on tested bacteria. Other extracts, including P. betel and P. guajava, were less effective, while A. sativum showed no effects against bacteria. In safety assessment experiments, we observed that only crude extracts of R. tomentosa and A. satium were safe, while others significantly reduced their survival rates. HPLC showed that extracts of high antibacterial properties had rich phenol constituents. In addition, the phenolic profile of R. tomentosa showed the presence of piceatannol.Conclusion: Considering both of antibacterial effects and safety properties altogether, we concluded that among the five examined plant materials of this study, R. tomentosa had the highest potential to apply in AHPND treatment, as only this plant showed the high effects on pathogenic bacteria while were still safe for host aquatic shrimps.