Vol. 23 No. 10 (2025): Tạp chí Khoa học Nông nghiệp Việt Nam

The oriental river prawn (Macrobrachium nipponense, de Haan 1849) is a freshwater crustacean species with high economic value and strong development potential. The success of artificial reproduction greatly depends on broodstock conditioning and the method of egg incubation. This study aims to determine the appropriate broodstock rearing density and incubation method in river prawn seed production. In this experiment, male and female prawns were reared at densities of 50, 100, and 150 individuals per square meter in tanks, using commercial feed for white-leg shrimp with a protein 40% and lipid 7%. The results showed that at a rearing density of 50 individuals/m², the survival rate (71.0%) and maturation rate (79.1%) were significantly higher ( P <0.05) compared to the densities of 100 and 150 individuals/m². During the broodstock maturation process, female prawns carrying eggs on days 9-10 were selected to test two egg incubation methods: natural incubation (eggs carried by the female) and artificial incubation (eggs removed from the female and incubated separately). After 9 days of observation at temperatures ranging from 24.5 to 26.5°C, the results showed that natural incubation achieved a higher hatching rate (80.4%) compared to artificial incubation (71.8%). However, artificial incubation offers advantages in environmental control and is more suitable for large-scale production.

This study aimed to evaluate the effects of two probiotic products (Bacillus spp.: Biofloc02 and ProbioAqua) and the chemical compound benzalkonium chloride (BAC) on the growth of green microalgae and cyanobacteria under both laboratory and field conditions. The results showed that all three treatments reduced the cell density of the green alga Chlorella vulgaris, with BKC causing a rapid decline from day four, while the two probiotic products exhibited a milder effect, likely due to nutrient competition. For Arthrospira platensis, all treatments inhibited growth, with BKC causing complete mortality within four days. Similar trends were observed in freshwater nursery ponds, where the overall densities of green algae and cyanobacteria also declined. Algal density in treated ponds did not increase during 7-day trial. The findings provide practical insights into the effectiveness and impacts of commonly used algal control products in freshwater aquaculture, contributing to informed decision-making when selecting appropriate management strategies for pond ecosystems.

This study investigated the production process of smoked shrimp sausage from whiteleg shrimp, a plentiful resource in Vietnam. The objective was to identify factors affecting product quality, including raw material ratios, additive content, grinding time, and smoking duration. Experiments were conducted in laboratory conditions using sensory evaluation and shear force measurement. The results suggested production process with a raw material ratio of pork meat/peeled shrimp/pork fat at 25/60/15, adding 5% modified starch, 2% egg white powder, and 0.4% sodium tripolyphosphate. Grinding for 5 minutes and smoking with lemon wood chips at 90-100°C for 120 minutes yielded the best shear force and sensory scores. The final product achieved a sensory score of 18.4/20 with a shear force of 11.5 ± 0.2 N, rated good according to TCVN 3215-79. This research contributes to enhancing shrimp value for convenient food production.

This study aimed to evaluate the impact of key environmental factors on the growth of Streptococcus iniae, a pathogenic bacterium affecting Pompano (Trachinotus spp.), under in vitro conditions. Fish samples (n = 54) exhibiting exophthalmia and hemorrhages, collected from Quang Ninh, Hai Phong, and Ninh Binh, were used for bacterial isolation. Bacterial identification was performed through morphological analysis, biochemical characterization, PCR techniques, and experimental infection. A representative S. iniae isolates from each province was utilized to assess the effects of temperature, pH, and salinity on bacterial growth. A total of nine S. iniae strains were successfully isolated and identified. The evaluation of environmental influences after 36 hours of cultivation on three representative isolates revealed that S. iniae can grow within a temperature range of 15-45°C, with optimal growth observed between 25-40°C. The bacteria grow well at pH of 6-8, with optimal at neutral pH (pH = 7). Additionally, S. iniae can survive and develop at salinities ranging from 0 to 60‰. However, its growth capacity tends to decline gradually with increasing salinity. The findings provide a scientific basis for developing strategies to prevent S. iniae-related diseases in pompano fish.

The study was aimed to determine the effects of these factors on the survival rate and metamorphosis time from megalopa to early juvenile of mitten crab. Mitten crab larvae, megalopa, were collected from artificial breeding tanks of the Northern National Broodstock Center for Mariculture (under the Research Institute for Aquaculture 1) and arranged into 3 independent experiments: temperature; salinity and stocking density. The temperature experiment consisted of five levels: 18; 20; 22; 24C and the control (about 20-22C). The survival rate tended to increase but the metamorphosis time shortened when the water temperature increased from 18; 20 to 22C, respectively, 22.0; 28.0; 34.1% and 299.8; 237.3; 196.2 hours. Regarding salinity, the experiment was at the levels of 0; 5; 10; 15‰ and control (about 22‰). The results showed that at salinity of 5‰, the survival rate was 36.0%, much higher than other salinities. When the salinity of the nursery water increased, the metamorphosis time was prolonged, respectively 163.5; 172.6; 194.3; 211.5 and 230.2 hours. Experiments with stocking density at levels of 5; 10; 20 and 30 megalopa/liter showed that stocking density exerted great influence on the survival rate and metamorphosis time from megalopa to early juvenile. The survival rate decreased significantly and the metamorphosis time tended to be prolonged when stocking density increased.

This study aimed to evaluate the biological characteristics of the red bigeye (Priacanthus macracanthus Cuvier, 1829) in the central coastal region of Vietnam. The biological characteristics were analyzed based on fishery biological data collected in the study area from January to December 2019, involving 1,798 individuals. The results indicated that the total length (TL) distribution ranged from 70 to 273 mm, with an average of 137.9 ± 0.97mm. The total length-body weight relationship was estimated as W = (7.41e – 5) × TL(2.69), with R² = 0.98. The von Bertalanffy growth function of the red bigeye was calculated as TLt = 294 × (1 – e-0.97 × (t – 1.058)). The total mortality rate (Z), fishing mortality rate (F), and natural mortality rate (M) were assessed at 2.94 yr⁻¹, 1.99 yr⁻¹, and 0.94 yr⁻¹, respectively, and the exploitation rate (E) was 0.68. Females were dominant throughout the study period, with a male-to-female ratio of 0.75:1. The red bigeye spawns once a year with the spawning season extending from July to October and peaking in August and September. The estimated length at first maturity (TL₅₀) was 190.9mm. The results indicated that the red bigeye population is dramatically overexploited in the central coastal region of Vietnam.

A study on the reproductive biology of river catfish Silurus asotus Linnaeus, 1758 was conducted from May 2024 to May 2025 that is a scientific basis for developing artificial breeding protocols, and conserving and enhancing the genetic resources of this species. Monthly samples were collected from the Hòa Bình hydropower reservoir and transferred to Northern national Freshwater Aquaculture seed Center for analysis of condition factors including fat indices, gonadosomatic index (GSI), fecundity, and gonadal development stages. Results showed that the condition factor (CF) of females ranged from 0.0077 to 0.0242, and of males from 0.0035 to 0.0134, this factor is highest and lowest in May and December, respectively. The Fulton and Clark fat indices of females reached their highest levels in December (Fulton: 1.24%, Clark: 0.95%) and their lowest in June (Fulton: 0.38%, Clark: 0.28%) while the GSI peaked in June (females: 17.2%, males: 3.5%) and dropped to 0% in November and December. The mean relative fecundity was 71,040 eggs/kg, and the mean absolute fecundity was 157,758 ± 14,224 eggs per female. This study confirmed that female fish weighing 3.5-4.5kg and males weighing 2.0-2.5kg are most suitable for artificial reproduction, and the time for artificial reproduction is mainly from May to August.

This study investigated biological characteristics of white-spotted rabbitfish in the northern coastal waters of Quang Tri province, Vietnam. The analysis was based on fishery biological data collected from January to December 2024 with 1,544 individuals. The results showed that the distribution of length ranges from 61 to 192mm FL (fork length) with an average of 138.8 ± 0.66mm FL. The fork length-body weight relationship was expressed with the equation W=(0,206e – 4) × FL(2,91925) with correlation coefficient r = 0.97. The von Bertalanffy growth function of white-spotted rabbitfish was expressed as FLt = 210 × (1 – e-0.7 × (t – 0.8705)). The total mortality (Z), fishing mortality (F), and natural mortality (M) were estimated as 3.17 yr(-1), 2.35 yr(-1), 0.82 yr(-1), respectively and the level of exploitation (E) was 0.74. Males were dominant throughout the period of study, male-to-female ratio was 1.55:1. The breeding season of white-spotted rabbitfish concentrated during March-June, with the peak in March. The first maturity length Lm50 was 151.4mm. The rabbitfish resource is being overexploited in the coastal waters of Quang Tri (E = 0.74) and this value exceeds the commonly recommended threshold (E ≈ 0.5). Further research is needed to convert this species into a marine aquaculture target to reduce the pressure on the exploitation of this species in the wild.

This study was conducted to isolate and screen Bacillus spp. as probiotic strains from water and sediment of Artemia culture systems. The research method includes sample collection, isolation, identification, preliminary screening and evaluation of Bacillus strains capable of producing extracellular enzymes, bacterial strain identification and safety assessment on Artemia. A total of 78 strains were isolated and characterized by morphological and physiological features similar to Bacillus genus by the conventional taxonomic method according to Bergey’s Manual (2015), which are rod-shaped cells, Gram-positive or negative, positive reactions to catalase and oxidase, motility and sporulation. Most isolates secreted extracellular enzymes (protease, amylase, and cellulase) capable of degrading casein, starch, and CMC, but 4 strains exhibited strong secretion of two types of extracellular enzymes by the spot-inoculated method. Notably, strain BC24.4 showed significantly higher protease and α-amylase activities (P<0.05) compared to the others. The result of the 16S rRNA gene sequencing showed that BC24.4 shared 99.3% similarity with Bacillus subtilis and safe on Artemia. Hence, strain BC24.4 is considered as potential for developing probiotic for enhancing degradation of organic matter in aquaculture systems, especially in Artemia culture ponds.

The study was conducted to provide data on species composition, diversity indexes, and community structure of plankton, contributing to the scientific foundation for biodiversity conservation efforts in the Dong Chau - Khe Nuoc Trong Nature Reserve. Samples were collected during two survey periods: the rainy season (November 2024) and the dry season (June 2025) at 10 representative water bodies. The study recorded 72 taxa of phytoplankton, belonging to 34 genera, 24 families, 19 orders, 4 classes, and 4 phyla. The phylum Heterokontophyta was dominant, accounting for 43% of the taxa. The number of taxa ranged from 64 species (first survey) to 70 species (second survey). The density ranged from 5,627 to 86,625 cells/l, with an average of 19,181 cells/l. The Shannon-Wiener diversity index (H’) ranged from 1.55 to 2.20, averaging 1.83, indicating a relatively low level of diversity. As for zooplankton, the study recorded 28 species and species groups, belonging to 9 orders, 20 families, and 19 genera. The Copepoda group accounted for the highest proportion of species (39%), with slight increase in the number of species and groups between the two survey periods. The density ranged from 240 to 580 individuals/m3, averaging 407 individuals/m3. The H’ index ranged from 1.87 to 2.49, with an average of 2.26, indicating a moderate level of diversity.

The study aimed to evaluate the current status of exploitation of Pangasius krempfi fingerlings in the estuaries of the Tien and Hau rivers. Primary data were collected by interviewing 75 households using stow nets and push nets from December 2024 to April 2025. The results showed that the fishermen operated for about four months each year, from August to November in the lunar calendar. The stow net caught about 5,200 fingerlings/net/year in the estuaries of the Hau river and 8,700 fingerlings/net/year in the estuaries of the Tien river, while the push net caught 27,800 fingerlings/ship/year and 27,500 fingerlings/ship/year, respectively. The push net in the Hau estuary was more financially efficient than that in the Tien estuary, with benefit and cost ratios of 0.54 and 0.17, respectively. Most of the fishermen reported a decline in fingerling yield and significant fluctuations in the number of exploiting households between the two areas. Some solutions for managing and protecting Pangasius krempfi fingerlings include continuing to raise fishermen's awareness of protecting aquatic resources, promoting and supporting livelihood conditions for fishermen in estuarine areas, and developing Pangasius krempfi fingerling production.

The study aimed to research status of livelihood capitals and propose solutions to improve the livelihood of households engaged in integrated mangrove-shrimp farming model through interviewing 92 households in Ngoc Hien, Ca Mau province. The survey results indicate that the shrimp–mangrove farming model yields significant economic benefits while maintaining environmental sustainability. Experienced households effectively utilized both natural and physical capital in this integrated system. Additionally, social capital was relatively strong, as residents have access to credit and actively participate in socio-economic organizations such as cooperatives, production groups, and women's unions. Facilities for production and supporting lives were well equipped. The total income of the household was 139.5 million VND/year/househol, equivalent to 35.8 million VND/year/per capita. However, the level of livelihood diversity was still quite low, putting pressure on natural capital. Based on the analysis, this study proposes a set of solutions aimed at enhancing local livelihoods. Key recommendations include increased investment in education, vocational training programs, capacity building for livelihood diversification, and the implementation of policies to strengthen the role and effectiveness of cooperatives.

The abalone species, H. diversicolor, is a high-value marine gastropod widely distributed in tropical and subtropical coastal waters, including Vietnam. In response to the decline of wild seed resources, artificial seed production has emerged as a key strategy for resource restoration and sustainable aquaculture development. This paper provides a comprehensive review of domestic and international studies on the reproductive biology of H. diversicolor, encompassing gonadal development, reproductive seasonality, environmental drivers, spawning behavior, and hatchery/ induced - spawning techniques. Comparative analysis indicates that countries such as Japan and South Korea,.. have adopted advanced molecular biotechnology and seed production protocols, whereas Vietnam still faces significant gaps in research capacity and technological readiness. The review also highlights existing knowledge gaps, particularly in reproductive endocrinology and the critical bottleneck during the metamorphosis from veliger larvae to spat. Building upon this critical review, the authors propose future research directions aimed at enhancing artificial seed production efficiency, ensuring a reliable supply of high-quality seed, and fostering the sustainable development of abalone aquaculture in Vietnam.