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Nghiêncứuảnhhưởngcủanhiệtđộnướcthấpđếnsựgâybệnhcủavirútđốmtrắng(WSSV) trêntômhe NhậtBản(Marsupenaeusjaponicus)

Dang Thi Lua, Ikuo Hirono

Received: 08-07-2015 / Accepted: 09-12-2015
Vi rút đốm trắng (WSSV) là vi rút gây bệnh có độc lực mạnh trên tôm nhưng dễ bị ảnh hưởng bởi các yếu tố gây sốc. Các biện pháp khống chế WSSV đã và đang được nghiên cứu nhưng vẫn chưa được áp dụng vào thực tiễn, do vậy việc quản lý môi trường nhằm hạn chế các yếu tố gây sốc đóng vai trò quan trọng trong việc ngăn ngừa bệnh WSSV. Nghiên cứu này đánh giá ảnh hưởng của nhiệt độ nước, đặc biệt là nhiệt độ nước thấp, đến khả năng gây bệnh của WSSV trên tôm he Nhật Bản. Kết quả nghiên cứu cho thấy tỷ lệ tôm chết sớm và cao nhất, lên tới 100% sau 7 ngày gây nhiễm WSSV, đã quan sát thấy ở nghiệm thức tôm nuôi ở 25oC, tiếp đến là ở nghiệm thức tôm nuôi ở 20oC và tỷ lệ chết thấp nhất ở nghiệm thức tôm được giữ ở 15oC. Nghiên cứu cũng cho thấy, tỷ lệ tôm chết xuất hiện muộn và thấp hơn ở tôm thí nghiệm nuôi ở 25oC nhưng được hạ nhiệt độ xuống 15oC sau khi gây nhiễm khi so với tôm trước và sau khi gây nhiễm đều giữ ở 25oC. Ngược lại, tỷ lệ tôm chết tăng lên ở nghiệm thức tôm giữ ở 15oC sau đó được nâng lên 25oC sau khi gây nhiễm khi so với nghiệm thức tôm giữ ở 15oC trước và sau khi gây nhiễm. Kết quả này được kiểm chứng bằng kỹ thuật PCR và RT-PCR. Kết quả nghiên cứu cho thấy sự gây bệnh của WSSV trên tôm he Nhật Bản phụ thuộc vào nhiệt độ và tôm mẫn cảm nhất với WSSV ở nhiệt độ khoảng 25oC. Nhiệt độ thấp (khoảng 15oC) đã làm chậm sự nhân lên của WSSV trên tôm nhiễm bệnh và ở nhiệt độ này tôm được xem như là nguồn mang mầm bệnh WSSV tiềm ẩn, khi nhiệt độ nước tăng lên bệnh sẽ bùng phát.
Characteristics of Shrimp Resources in the Coastal Waters of Hai Phong - Quang Ninh

Vo Trong Thang, Nguyen Van Giang

Received: 07-07-2022 / Accepted: 27-01-2023
This study was conducted to identify the current status shrimp resources in the coastal of Hai Phong-Quang Ninh. From 2013-2019, a total of 88 hauls were collected during four surveys representative for the Northeast and Southwest monsoon seasons by a single-shrimp trawler. The survey was conducted applying the fixed sampling stations. Research results identified 53 species of shrimp in 23 genera belonging to 10 families, of which the Penaeidae family was most abundant with 29 species. Research results updated and supplemented 25 shrimp species, including 12 white shrimps and eight mantis shrimps, and identified 25 commercial shrimp species in the study area. Shrimps contributed to 18.31% of the total catch, their proportion in the coastal waters was 30.34% higher than in the inshore (12.92%). The average shrimp yield in the Southwest monsoon season was higher than in the Northeast, with an average was 7.31 kg/h. The average biomass density in the study area was 303.56 kg/km2, and the stock of shrimp was estimated at 2,494 tons in the Northeast monsoon season and 5,116 tons in the Southwest monsoon season. The present study provided the information for protecting and sustainably exploiting shrimp resources in the research area.
Technical Efficiency of White-Leg Shrimp (Litopenaeus vannamei)Culture over Winter Crop Between Outdoor Ponds and Indoor Shrimp Production System in Nam Dinh Province

Nguyen Huu Vinh, Dang Thi Hoa, Le Thi Cam Van, Doan Thi Nhinh, Tran Thi Trinh, Do Hoang Hiep, Truong Dinh Hoai, Kim Van Van, Pham Thi Lam Hong, Le Viet Dung

Received: 13-05-2021 / Accepted: 03-06-2021
The Indoor Shrimp Production System (ISPS) with the treating water systems at low temperature was developed in Japan. This study evaluated the applicability and technical efficiency of growing white-leg shrimp in the ISPS under Vietnamese conditions. Two ponds in the ISPS were compared with two outdoor ponds overwinter in Nam Dinh. The ISPS ponds showed a better yield (51.84 ± 1.45ton/ha) and growth of shrimp (0.175 ± 0.006 g/day) compared with the outdoor ones. The phytoplankton communities of the two treatments were diverse; however, the cyanobacteria density in the ISPS pond water (<104cell/ml) was lower than the outdoor water (> 104cell/ml). The density of Vibrio parahaemolyticusin the ISPS pond water (0.6 101- 4.4 101CFU/ml) was lower than that in the probiotic one (1.2 103- 2.1 103CFU/ml) over 11 weeks. In addition, the total Vibrio and V. parahaemolyticus densities of the shrimp’s hepatopancreas in ISPS ponds (2.3 102 - 3.2 103CFU/ml và 1.1 102- 8.9 102 CFU/ml, respectively) were lower than those in the outdoor ones (1.5 103- 1.6 104CFU/ml và 8.3 103 - 9.8 103CFU/ml, respectively). The results demonstrated the potential applicability of the ISPS in culturing shrimp in the North of Vietnam.
Survival and Growth Ratesof White-Leg Shrimp Litopenaeus Vannamei(Boone, 1931) Reared in Freshwater and Saline Brackishwater

Le Viet Dung

Received: 24-09-2018 / Accepted: 07-11-2018
This study compared the growth and survivalratesofwhite-leg shrimp (L. vannamei) which were reared in freshwater at 0 ppt and in saline brackishwater at 30 ppt. PL34 shrimps were reared at the density of 1 individiual/L (200shrimp/m2) for 21 days. Shrimps of each treatment were reared in three 40 L tanks. Results showed that there was no significant difference in survival and growthratesofthe white-leg shrimpshrimpbetween the two treatments during the whole culture period. The survival rates of shrimp reared at 0 ppt and 30 ppt were 62.5 ± 10.9% and 69.17 ± 7.64%, respectively. The weight gain of shrimp reached113.33± 15.28% for shrimp at 0 ppt and 106,67± 11,55% for those at 30 ppt. The specific growth rate of shrimp at 0 ppt and 30 ppt was 3.78 ± 0.36% and 3.63 ± 0.28%, respectively.In conclusion, white-leg shrimp could be reared in freshwater 0 ppt.
Disease Risk Management in ShrimpFarmingin the Coastal Areasof Nam DinhProvince

Nguyen Thi Minh Thu, Tran Dinh Thao

Received: 09-07-2019 / Accepted: 05-08-2019
The study aims at analyzing the situation to recommend measures to improve disease risk management in shrimp farming in Nam Dinh province. The study was conducted in three coastal districts, including Giao Thuy, Hai Hau and Nghia Hung. The data was collected through surveys with 120 shrimp farming households and note taking records in 910 shrimp pondsto analyze the disease’s likelihood, damages and households’ risk management strategies. In Nam Dinh, within 2010 and 2016, the shrimp farming area reduced from 3.632 to 2.834 hectares, corresponding to 59.52 to 45.30% of the total aquaculture area in brackish water. Over 80% of total shrimp pondssuffered loss fromdiseaseswithin 2015 and 2016. The disease risk managementcoastal areas could be improvedthroughvarious measures, including efficiency improvement in the state management in aquacultureareaplanning, infrastructuresynchronization, capacity building for the shrimp farmers,quality controlof aquacultureinputs, financial market development, agricultural insurance, promotion of the production-consumptionlinkage, and formation of value chain for the shrimp productin coming years.
Polyculture of Whiteleg Shrimp (Litopenaeus vannamei) and Red Tilapia (Oreochromissp.) -A Response to Climate Change inGiao Thuy District, Nam Dinh Province

Kim Van Van, Ngo The An

Received: 05-02-2017 / Accepted: 09-03-2017
This study aimedat examining the model of integrated culture of whiteleg shrimp with red tilapia in the context of climate change (CC), an expectation for a good model for the local farmers to deal with climate change. The experiment was carried out in six ponds, ranging from 2000 to 2500 m2, in 2015 and 2016, in Giao Phong commune, Giao Thuy district, Nam Dinh province. The trials consistedof 6 models designed in six ponds: two integrated farms in freshwater, and four monoculture shrimp farms for control, two in brackish water and two in freshwater. In the integrated culture models, red tilapia was added at a density of 2 fish per m2to a pond stocking 100 white shrimp per m2; the shrimp were stocked twice but red tilapia was stocked only once per year. In the monoculture models, whitelegshrimp was stocked at the same time and the same density as those in the integrated models. Comparingto the monoculture of shrimp in both brackish and fresh water, the polyculture of shrimp with red tilapia where whitelegshrimp was acclimatized to fresh water resulted in lower disease incidence, reduced the cost of drugs and chemicals by about 30%, and gained more than doubled the economic benefits. Farmers and the local authorities in the district highly appreciated the results of the integrated culture model. This model can be considered as a strategy to increase the adaptive capacity of aquatic production in the study area.
Productive Efficiency of Intensive White-Leg Shrimp Farming Households in Phu Yen Province

Le Kim Long

Received: 15-03-2017 / Accepted: 19-05-2017
Shrimp is the major commodityin the annual export turnover of Vietnam. This paper analyzedproductive efficiencyof the intensive white-leg shrimp farming households in Phu Yen. A total of 59 shrimp farming households practicing intensive aquaculture with the area of 45 ha (about 24% of the intensive white-leg shrimp farming in Phu Yen province) were randomly surveyed. The result showedthat although the intensive white-leg shrimp farming in Phu Yen is still profitable,but the interest for investment in shrimpfarming is rather low due to high risk and high productive capital. Moreover, this aquaculture is only profitable if its negative impact on the environment is neglected. The saturation state due to open-access mechanism for aquaculture has, however, been reached. Toward a sustainable aquaculture, it requires a further revision and issuing policies that step by step endogenize the environmental costs into the production process. Farmers’supports such as technology development, technique training and credit acess are also important.
Assessment of the Possibility White Spot Virus Infectionfrom Red Fiddler (Ucasp.) to White Shrimp (Litopenaeus vannamei)

Truong Thi My Hanh, Huynh Thi My Le, Pham The Viet, Phan Thi Van

Received: 28-02-2017 / Accepted: 10-04-2017
White spot syndrome virus (WSSV), the causative agent of white spot syndrome in shrimp, has a wide host range includingcrabs, zooplankton (Copepods), molluscs, poultry and polychaete.Ucasp.isa common fiddler living in intertidal land, estuary and sourcewaterused for settling pond of shrimp farmsin Nam Đinh, Nghe An and Quang Ninh. WSSV, an important viral pathogen of the shrimp, can replicate in crustacean species,therefore, it is a potential vector for virus transmission. The major aim of this study was to determine whether WSSV can be replicate on Ucasp and transmitted from Ucasp. to shrimp (Litopenaeus vannamei) through water environment. Uca sp. wasinfected withWSSV by injecting suspension containing WSSV in dilution 10-2on the second leg. Results showed that, WSSV was detected in infected fiddler in experimentby PCR method after 107 hours of infection. WSSV was transmitted from Ucasp. to shrimp through water environment horizontally after 83 hours of exposure to Ucasp. carrying WSSV. Our findings support the contention that Ucasp. was a potential vector for virus transmissionandcan be a source of WSSV infection of culture shrimp.
Assessment and Selection of Coastal Shrimp Farming Models Adaptable to Climate Change in Quynh Luu District, Nghe An Province

Bui Dac Thuyet, Nguyen Huu Nghia, Phan Thi Van

Received: 20-12-2016 / Accepted: 15-02-2017
This study aimedto assess and identifycoastal shrimp farming modelsthat are sustainable under climate changeconditions in Quynh Luu, Nghe An. The evaluation criteria focusedon infrastructure (6 criteria), culture techniques and cage management (7 criteria), and awareness of and response to climate change (2 criteria). Each criterion was assessed andscored on a 5 point scale (5 = very good, 4 = good, 3 = average, 2 = poor, 1 = weak). The assessment results found that most criteria were averaging upwards, except criteria on influent and effluent systems, reservoir and site location of the shrimp farm TNT2. Coastal shrimp farms (TNT1, TNT6) had a high overall score and thus can be selected as the coastal shrimp farming modelsfor the coastal shrimp farming community in this location.
Factors Affecting Intention to Choose Crab - Shrimp - Rice Farming Model in Kien Giang Province

Le Ngoc Danh, Nguyen Thi Kim Phuoc, Le Hong Hanh

Received: 06-09-2021 / Accepted: 21-01-2022
The study uses a binary regression model, rational action (TRA) theory, and the theory of intentional behavior (TPB). The study's objectives are to determine the factors affecting the intention to choose the farming model of crab - shrimp - rice of farmers in Kien Giang province. The results of the analysis of 102 extensive crab-shrimp-rice farming households showed that male respondents accounted for 82.4%, the average age of the household head was 51 years old, the average education level of the household head was 7th grade. The average number of years of experience of the household head was 10 years, the average area of the household was 2.8 ha. The results of binary regression analysis showed that 9 variables (education, training, experience, area, salinity, increased profit, model fit, impact of people around, and model implementation ease) influenced the intention to choose the farming model of crab-shrimp-rice of farmers. From the research results, the following solutions were proposed: Farmers’ management of all kinds of risks during the productionand consumption of shrimp and rice,regular monitoring of weather/environmental studies or forecasts,selection of seed sources and inputs (feed, lime, antibiotics) from reputable establishments,participating in local trainingandsqueezing the shrimp back before putting them in the pond.
Effectof Stocking Density on Growth Rate and Survival of White Leg Shrimp, Litopenaeus Vannamei,Raisedon Indoor Composite Tanks

Nguyen Phuong Toan, Vu Van Sang, Nguyen Viet Vuong, Nguyen Quang Tuat, Dang Thi Diu, Doan Thi Nhinh, Tran The Muu, Vu Van In

Received: 18-02-2013 / Accepted: 20-04-2013
The effect of stocking density of white leg shrimp SPF (Litopenaeus vannamei) was carried out at different density of 40, 60 and 80 PL15/m2 for 75 days. Each treatment was replicated three times in 4m2 indoor composite tank system and feeding ratio of 10-15% body weight with CP pellets containing 38% crude protein and four times a day. During the experiment, water temperature varied between 28 and 31ºC, whereas salinity ranged from 20-24‰ in biosecurity condition. Water in the culture tanks was renewed 50% weekly. The highest growth rate in weight was found in treatment of 40 heads/m2 (1.54 g/week), followed by 60 heads/m2 (1.47 g/week) but the rate for 30 heads/m2 (1.16 g/week) was lowest. Similarly, the survival rate of shrimp stocking at 40 heads/m2 ranked highest (79.7 ± 2.6%), followed by 60 heads/m2 (78.7 ± 2,9%) and the lowest rate for the 80 heads/m2 (70,3 ± 3,3%; P<0.05). Nevertheless, there was no significant difference in the survival rate between shrimp raised at 40 heads/m2 and 60 heads/m2 (P>0,05). Size variation (CV) for 40 heads/m2 (727 ± 1.52%) and 60 heads/m2 (8.22 ± 2.5%) were considerably lower than that for 80 heads/m2 (12.9 ±2.7%; P<0.05). However, there was no considerable disparity in feed conversion rate among the three treatments (P>0,05). All shrimp sample tissues were found negative for WSSV, YHV, TSV, MBV and IHHNV.
Effect of Salinity Stress Shock on Growth and Survival of Black Tiger Shrimp(Penaeus monodon) at the Nursery Stage in the Biofloc Technology System

Huynh Thanh Toi, Nguyen Thi Hong Van

Received: 16-12-2017 / Accepted: 16-04-2018
This study was conducted to evaluate the effect of salinity stress shock on the growth and survival of postlarval black tiger shrimps (Penaeus monodon). The experiment consisted of 7 treatments. In five treatments for salinity stress, the shrimps taken from 20‰salinity condition were abruptly transferred to 5‰, 10‰, 15‰, 20‰, and 30‰salinity environment. In other two treatments the shrimps reared at 20‰salinity were acclimated for short time (in 3 hours) and long time (in 3 days) to 5‰salinity by adding tap water at stocking density of 2 shrimps/L . After 20 days of nursing, the water condition was in a suitable range for shrimp growth. The growth of shrimp in terms of individual length and weight by sudden salinity changes was not significantly different compared to the control, but the survival was significantly lower. The highest survival rate (98,3%) was observed in the control (20‰) and the lowest survival (60,7%) was found in the salinity shock from 20‰to 5‰. The results indicated that the survival of shrimps was adversely affected when salinity was suddenly shocked at high threshold by 10 - 15‰while the increase in salinity from 20‰to 30‰did not affect shrimp survival. Both short time and long time acclimation did not affect the shrimp survival and growth.
Diversity of Zoobenthos in the Shrimp Culture Area in Ca Mau Province During Rainy Season

Au Van Hoa, Tran Trung Giang, Nguyen Thi Kim Lien, Huynh Thi Ngoc Hien, Vu Ngoc Ut, Huynh Truong Giang

Received: 05-07-2021 / Accepted: 21-01-2022
The study aimed to determine the species diversity and composition of the benthic communities during the rainy season within the shrimp culture areas in Ca Mau province. The purpose of this study was to find the changes in species composition, and density distribution within the shrimp culture area as the basis for biological monitoring of the water quality in brackishwater shrimp farming areas. Benthic samples were collected at 9 sites in June and September, 2019. The results showed a total of 34 benthic species belonging to 31 genera, 24 families, 16 orders, 5 classes and 3 phylums. The number of species were variation among the sampling sites, from 2 to 11 species with a density ranged from 9 to 2,547 inds/m2. There were 23 benthos species identified during June, lower than those in September with 25 species. Additionally, the density of the zoobenthos in June were observed 2.5 times higher in comparison to those in September. The species composition and density of Gastropoda were highest within the study area. The similarity of the distribution of benthos was 18.9% at 9 sampling sites and divided into three groups. Shannon diversity index (H') ranged from 0.3 to 1.8, which indicated that the benthic diversity richness characterized by sampling location and time was low to moderate in the shrimp culture areas during rainy season.
Development of Agro-Based Clusters in Vietnam: Case Study in Shrimp Sector of the Mekong River Delta

Luu Van Duy, Nguyen Phuong Le, Le Thi Thu Huong

Received: 24-05-2023 / Accepted: 05-10-2023
In the context of globalization, the agricultural sector of Vietnam is transforming to improve competitiveness in the global market. One of the potential solutions is the formation and development of agro-based clusters. This study aimed to analyze the preconditions of the development of shrimp clusters in the Mekong River Delta. Based on secondary data and primary data from a survey with 180 samples of five key actors across three provinces in the region, the study found out that, the Mekong River Delta possessed several favorable conditions in terms of natural and social conditions and the concentration and specialization to develop the shrimp clusters. However, conditions such as operating institutions, and the leading role of key enterprises in co-operation in production and business were the main barriers hindering the development of the shrimp clusters. Therefore, the policy of agro-based cluster development for the shrimp sector should give priority to regional spatial reorganization, reorient production organization, enhance innovation, and strengthen support for actors involved in agro-based clusters.
Growth and Survival Rate of SPF Vannamei Broodstock Candidate (Litopenaeus vannamei) Cultured in Indoor System at Different Stocking Density on Cat Ba Islands, Hai Phong

Vu Van Sang, Le Van Nhan, Nguyen Phuong Toan, Nguyen Huu Ninh, Tran The Muu, Vu Van In

Received: 03-08-2012 / Accepted: 25-09-2012
Litopenaeus vannamei) cultured in biosecurity system. Three groups of experimental shrimp (initial weigh 20.1±1.9 g/male and 21.4±2.2 g/female) were stocked at densityof10, 20 and 30 heads/m3in4m3indoor tank system. Each treatment was run in triplicate and fed with about 4% shrimp weight daily with pellet diets of CP 7704S and 7704P (38% crude protein), feeding four times a day. The water temperature ranged from 20.0 - 28.5oC and salinity ranged from 20-28‰. Water was renewed 80% volume weekly. The highest growth rate in weight was recorded in broodstock candidates cultured at 10 heads/m3(1.03 g/week/male; 1.11 g/week/female), followedby 20 heads/m3(0.89 g/week/male; 0.98g/week/female) and the least for 30 heads/m3(0.53 g/week/male; 0.62 g/week/female). Similarly, survival rate of shrimp at 10 heads/m3(71.7 ± 2.7%) ranked highest and the lowest rate for the 30 heads/m3 (60.1 ± 2.8%; P<0.05). Nevertheless, there is no significant difference in the survival rate between shrimp cultured at 10 heads/m3(71.7% ± 2.7%) and 20 heads/m3(71.5 ±3.0%; P>0.05). Size variation (CV%) and FCR recorded on 10 heads/m3 (CV%: 6.34 ± 1.12%; FCR: 2.78 ± 0.5) and 20 heads/m3(CV%: 6.68 ± 1.20%; FCR: 2.86 ± 0.3) were found remarkably lower than that for 30 heads/m3(CV%: 10.56 ±2.24%; FCR: 3.42 ± 0.8; P<0.05). The percentage ofshrimp harvested thatmet the criteria of broodstock was 67.1 ±2.6% and 66.7 ± 3.2% for the 10 and 20 heads/m3, respectively, whereasonly 23.1 ± 5.4% for the 30 heads/m3. All shrimp sample tissues were found negative for WSSV, YHV, TSV, MBVandIHHNV.
Comparison of Technical and Economic Efficiency of Specialized Artemia Culture Model and Artemia-Shrimp Rotation Model in Coastal Area of Soc Trang

Huynh Thanh Toi, Tran Thi Kim Muoi, Nguyen Thi Hong Van

Received: 19-02-2020 / Accepted: 04-08-2020
The study was conducted to compare the technical efficiency and economic efficiency of the two models of specialized Artemia culture and Artemia-shrimp rotation to make recommendations for a suitable farming model that brings high economic efficiency foraquaculture farmers in that area. Data of the study were collected by directly interviewing 60 Artemiafarmers with relevant information on Artemiaculture and other aquatic species in the 2018 coastal area of Soc Trang province. The results show that in the dry season, most of the households cultivate only Artemia, Artemiacyst production with an average return of 66 million VND/household/year, the rate of returns is 1.59. In contrast, while in the wet season, the land is used for alternately rearing other aquatic animals (about 55% of total area), the returns are quite high for the Artemia - shrimp alternative model reaching 194 million/crop/year, the rate of returns is 2.1. Based on the survey results, it is necessary to consider the investment and expansion of the Artemia- shrimp alternation model, encouraging households to uses 100% land for aquaculture which aims to stabilize the economy for households.
Study on the Virulence Factors ofVibrio parahaemolyticusCaused Acute Hepatopancreatic Necrosis Disease (AHPND) in Farmed WhiteLegShrimp (Litopenaeus vanamei) in Thua Thien Hue Province

Nguyen Ngoc Phuoc, Nguyen Thi Xuan Hong, Nguyen Cong Chung

Received: 13-03-2020 / Accepted: 24-04-2020
The aim of this study was to identified the virulence factors and the pathogenesis of Vibrio parahaemolyticusin farmed white leg shrimp in Thua Thien Hue province. In this study, 8 isolates of V. parahaemolyticuswas recovered from diseased white leg shrimp that showed typical clinical signs of AHPND such as pale-to-white hepatopancreas (HP), significant atrophy of the HP, softshells, guts with discontinuous, or no contents, black spots or streaks visible within the HP. The bacteria were identified as V. parahaemolyticusby using API 20E kit (BioMerieux). Four of 8 isolates have been detected that caused AHPND by using IQ Plus™ AHPND/EMS Plasmid Kit. Data of this study showed that the production of caseinase, phospholipase, haemolysin and mobility of these isolates were significantly stronger than others. The LD50 of isolate that caused AHPND was 105 cfu/mL. By contrast, experimental shrimp were healthy without any clinical signs and no mortality was observed in the treatment immersed in the isolate lacking toxin genes. This study showed strong relationship between virulence factors and pathogenesis of V. parahaemoliticus caused AHPND in shrimp.
Study on Enterocytozoon hepatopenaei (EHP) Diseases in White-leg Shrimpsin Quang Ninh and Nam Dinh Provinces

Truong Dinh Hoai, Dang Thi Hoa, Xa Duc Binh, Mai Van Thuong, Nguyen Thi Thuy Hong, Hoang Thi Thuy Linh, Tran Thi Diem Quynh, Tran Thi Trinh, Doan Thi Nhinh, Le Viet Dung, Kim Van Van, Truong Hong Viet

Received: 12-06-2023 / Accepted: 20-11-2023
This study aimed to determine the disease situation and disease characteristics caused by microsporidian Enterocytozoon hepatopenaei(EHP) in white-leg shrimps in farming areas in Northern Vietnam. Shrimp samples from 85 shrimp farms in Nam Dinh and Quang Ninh provinces were collected to conduct research. The detection results using the PCR assays determined that shrimp samples from 33 farms (38.8%) were positive for EHP. The analysis of diseased shrimps (n = 215) showed that the infected shrimps with EHP exhibited growth retardation (81.8%), muscle opacity, body shelling, and the appearance of larger "rice grains" in the caudal vertebra (85.1%). Diseased shrimps also showed signs of twisted intestines and intermittent food. Giemsa staining results from infected shrimp samples showed that EHP microspores were concentrated in the hepatopancreas organs the opaque muscle and “rice grains” of affected shrimps. Infected shrimps appeared mainly in the culture period from 30 to 60 days after stocking, accounting for 78.7%. The results of this study provide helpful information for the diagnosis and effective prevention measures for EHP in shrimps.
Effect of Rearing Density on Growth, Survival and Reproductive Performance of White Leg ShrimpBroodstockSPF (Litopenaeusvannamei)

Vu Van Sang, Nguyen Quang Trung, Vu Van In, Tran The Muu

Received: 03-09-2012 / Accepted: 15-12-2012
Three stocking densities of 6, 9, 12 heads/m2 of white leg shrimp broodstock SPF (Litopenaeus vannamei) were conducted in series of 14m2 indoor composite tanks at 28-29ºC and salinity of 28-30‰ under biosecurity control. Shrimp were fed 4 times a day with 50% blood worm and 50% fresh squid under water exchange of 100%/day. For induced breeding, eye ablation was applied to female after 30 days intensive rearing. There was no significant difference in growth, survival, rate of mating and spawning, fertilization and hatching rate among treatments (P>0,05). However, reproductive performance was significantly better in shrimp rearing at 6 and 9 heads/m2 than in those reared at 12 heads/m2 (P<0.05), reaching mature rate: 78.2-79.52%; number of spawning/female: 2.49-2.51; spawning fecundity: 152.600 - 153.200 eggs/female/spawn; average Nauplii/female: 123.9 - 127.5 x 103. Samples of broodstock shrimp, larvae and fresh food were found negative for WSSV, YHV, TSV, MBV and IHHNV.
Studies on designing and manufacturing of an automatic monitoring and warning systems for some environmental parameters in shrimp ponds

Dang Thi Thuy Huyen, Nguyen Kim Dung

Received: 16-02-2020 / Accepted: 06-07-2020
Our research was conducted to design and manufacture an automatic monitoring and warning system for shrimp ponds using three environmental parameters including pH, DO concentration, and salinity. Different from the manual measurement with KIT sets, hand-held meters requires many workers, or automatic monitoring of sensor network with nodes located in each pond often has a high cost, this study proposed the use of a measuring station to remotely monitor the water environment of ponds through an application installed on the smartphone. Water samples of ponds were pumped in turn to the measuring station, where parameters were determined, processed, and sent to the monitoring interface on a smartphone, and at the same time, providing timely warnings to the manager via text messages when these parameters are outside the allowed threshold. This research is not only applicable to the shrimp pond environment but also widely applicable in aquaculture. This is also an open direction in the application of automation in agricultural production. It is also possible to develop a monitoring system, automatic data storage of the pond environment, contributing to making the most effective management plan.
Effect of Ecological Zones of Fresh and Brackish Water on Rice Growth and Soil Chemical Characteristics in Rice-Shrimp System in Bac Lieu Province

Le Van Dang, Ngo Ngoc Hung

Received: 18-04-2018 / Accepted: 12-07-2018
The objectives of the study were to evaluate i) effect of ecological zones of fresh and brackish water on rice-shrimp cultivation systems, (ii) chemical characteristics of soil and water of the agro-ecological zones, and (iii) the efficiency of liming on rice growth and yield. Field experiments were conducted during August to December 2013 in Phuoc Long and Hong Dan, Bac Lieu province. Results showed that, after shrimp harvest, Phuoc Long planted rice crop in August when soil salt concentration was high (ECe: 8.0 mS/cm; ESP: 13.8%). Exchange cations in the soil decreased in the descending order: Mg2+>Na+>Ca2+>K+, corresponding to 8.0>3.0>1.5>1.0 meq/100 g, respectively. Due to salt accumulation in the soil in brackish water zone, ECe and ESP were at high levels during December (5,6 mS/cm and 7,8%, respectively), unfavourable for growth and yield of rice in comparison with fresh water zone at Hong Dan. Lime application to the salt-affected soil in Phuoc Long reduced salt damage to rice in terms of panicle number per square meter, filled grain rate, and higher grain yield (by 0.6 t ha-1) as compared to without liming. However, lime application to rice soil in fresh water zone at Hong Dan did not significantly increase the grain yield.
Bacillus sp. Isolated from Goose Grass (Eleusine indica) Enhances the Removal Efficiency of Ammonium in Shrimp Aquaculture

Do Quang Trung, Tran Thi Tuyet Thu, Luu The Anh

Received: 03-08-2021 / Accepted: 21-01-2022
Treatment of aquaculture wastewater by biological method is being more attractive to the scientists. This study aimed to screen the salt-tolerant and ammonia-oxidizing Bacillusendophytic bacteria having potential to reduce ammonium levels in shrimp aquaculture wastewater. In this study, eight Bacillusstrains were screened from endophytic bacteria isolated from gooose grass. Among these strains, two strains, MT50 and MT51 showed the highest efficiency for ammonium removal (80.36 and 82.24%, respectively). They optimally grew at pH of 7 and in highly salty condition (4% NaCl). Investigation in laboratory conditions for their ability in improving shrimp aquaculture wastewater showed that both Bacillusstrains had ammonium removal from 72.25 and 78.85% at day 7th. Notably, strain MT50 in combination with unsterilized shrimp-wastewater presented the highest ammonium removal efficiency (79.91%) with 1% cell suspension at day 4th. The results also showed the nitrite and nitrate production in all experiments and these compounds were removed by the selected Bacillusspecies. Results suggested that tưo Bacillussp. isolated might be used as heterotrophic nitrification-aerobic denitrification species.
Non-Vibrio ParahaemolyticusCausing Acute Hepatopancreatic Necrosis on Brackish Shrimps

Dang Thi Lua, Nguyen Viet Khue, Phan Thi Van

Received: 22-01-2016 / Accepted: 29-04-2016
Acute hepatopancreatic necrosis disease (AHPND), also known as Early Mortality Syndrome (EMS), has become one of the most harmful threats to the shrimp aquaculture industry in Southeast Asia, including Vietnam. It occurs on both tiger and white leg shrimps at 20 - 45 days of age with a mortality rate up to 100%. AHPND pathogens were identified as bacteria containing plasmid carrying toxin genes that cause acute hepatopancreatic necrosis. Observation of biochemical characteristics, the use of PCR technique using specific primers to detect the toxin genes and sequence analysis of 16S-rRNA gene confirmed that there were at least three strains of AHPND pathogenic bacteria on brackish shrimp cultured in Vietnam, of which two strains belong to Vibrio parahaemolyticus species, including V. parahaemolyticus KC13.14.2 and V. parahaemolyticus KC12.020; and the other strain of Vibrio sp. KC13.17.5. Vibrio sp. KC13.17.5 was confirmed as V. harveyi KC13.17.5, a non V. parahaemolyticus species. The detection of non - V. parahaemolyticus that caused AHPND is a new finding not only in Vietnam but also worldwide.
Species Composition and Distribution of Zooplankton in the Shrimp-Mangrove Field in Ngoc Hien District of Ca Mau Province

Phan Bao Tan, Au Van Hoa, Tran Trung Giang, Nguyen Thi Kim Lien, Vu Ngoc Ut

Received: 22-08-2023 / Accepted: 20-11-2023
The present study aimed to assess the species composition and distribution of zooplankton in the shrimp-mangrove fields at Ngoc Hien district, Ca Mau province. Samples were collected monthly from January to December 2022. At each sampling time, qualitative and quantitative samples of zooplankton were collected in 3 integrated shrimp-mangrove fields (3 points/field). Based on the morphological characteristics and external structure of zooplankton, the findings found 26 species of zooplankton belonging to 17 genera, 17 families and 5 different groups, viz.luding Protozoa, Rotifera, Cladocera, Copepoda and meroplankton were recorded. The number of zooplankton species in each month varied from 7 to 12 species, and the density ranged from 22,065 to 769,725 ind./m3. The highest density of zooplankton was found in June with a mean of 769,725±541,622 ind./m3. The species composition and abundance of zooplankton during the rainy season werehigher than those in the dry season. The distribution of Rotifera and Cladocera groups in the shrimp-mangrove fields was affected by salinity. The results found a number of zooplankton species such as Brachionus angularis, Brachionus plicatilis, Philodinasp., Diaphanosomasp., Oithonasp. and nauplius larvae of Copepoda had the potential as good food sources, that can be used for increasing biomass production and enrichment techniques for crustacean and fish larvae at the nursery stage.
Effect of Salinity Fluctuation Frequency on Molting Rate and Growth Performance of Postlarval White-Leg Shrimp (Litopenaeus vannamei)

Huynh Thanh Toi, Nguyen Thi Hong Van

Received: 03-01-2018 / Accepted: 17-08-2018
This study was conducted to examine the effect of salinity fluctuation frequency on molting rate and growth of postlarval white-leg shrimp (Litopenaeus vannamei). Individal shrimp was stocked in 5 L plastic bottle containing 2 L of 20 ‰ seawater with 04 treatments including salinity fluctuation in an amplitude ± 0‰ (NT1; ĐC), and an amplitude ± 5‰ with a frequency was set in 2 days (NT2), 4 days (NT3) and 6 days (TN4), 30 replicates each. The initial weight and length of postlarva was 0.007 g/ind. and 0.97 cm/ind., respectively. The results showed that the shorter molting frequency (4.9 days/times) and higher molting rate (22.1 %/day) were obtained in the treatment (NT4) where salinity fluctuation frequency was set in 6 days. In contrast, longer molting frequency (5.3 days/times) and lower molting rate (20.5 %/day) was obtained in the constant salinity treatment (ĐC). In addition, the highest growth in terms of weight after 45 days culture were obtained in NT4 (0.88 g/ind.), followed by NT3 (0.85 g/ind.), NT1 (0.83 g/ind.), and NT2 (0.74 g/ind.). The results of this study indicated that the higher molting rate and shorter molting frequency lead to significantly better growth of shrimps when salinity fluctuation in 6 days frequency was applied, compared to constant salinity.

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