Current status and biological characteristics of giant freshwater prawn (macrobrachium rosenbergii de man, 1879) cultured in the brackish water environment

MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY SUMMARY DISSERTATION OF DOCTOR DEGREE Subject: Aquaculture Code: 62 62 03 01 HUYNH KIM HUONG CURRENT STATUS AND BIOLOGICAL CHARACTERISTICS OF GIANT FRESHWATER PRAWN (Macrobrachium rosenbergii DE MAN, 1879) CULTURED IN THE BRACKISHWATER ENVIRONMENT Can Tho, 2016 THIS DISSERTATION WAS CONDUCTED AT CAN THO UNIVERSITY Promoter: Associate Professor Doctor: Tran Ngoc Hai Associate Professor Doctor: Do Thi Thanh Huong The dissertation will be defended at the university committee in … at: ….… hr ….… date …… Month………year……………… At………… hour…….day……….month…………2016 Examiner 1: Examiner 2: Examiner 3: The disseratation is available in Libraries: Learning Resource Center of Can Tho University National Library, Vietnam Chapter INTRODUCTION 1.1 Background Due to over-developing on Penaeid shrimp culture in recent years, there were many issues in shrimp cultivation caused by disease outbreak and environmental pollution In addition, in the increasing situation of climate change, sea level rise as well as saltwater intrusion, Mekong Delta is warned to be the vulnerable area affected hardly (Ministry of Natural Resource and Environment, 2009; 2012) The development of aquaculture systems in brackish water with different salinities has become important trend in order to adapt to these negative impacts of the mentioned issues Freshwater prawn is considered potential culture species in adaptation the situation According to Pham Van Tinh (2004), freshwater prawn was a species that can tolerate to the wide salinity range (0-25‰) The effect of salinity on freshwater prawn was also documented in some other previous domestic and international studies (Yen and Bart, 2008; Do Thi Thanh Huong et al., 2010; Nguyen Thi Em, 2008) that was a key basis to further studies to develop freshwater prawn culture in brackish water In reality, farmers in Mekong Delta also culture freshwater prawn in salinization area However, there were no full evaluations on suitability and economic efficiency of culture systems in brackish water up to now The study “Current status and biological characteristics of giant freshwater prawn (Macrobrachium rosenbergii De Man, 1879) cultured in the brackish water environment” was conducted to evaluate scientific basis, status, potential and solutions to develop freshwater prawn culture in brackish water; and contribute to sustainable aquaculture in Mekong Delta in the future 1.2 Objectives 1.2.1 General objective The general objectives of the study are to evaluate the status and to find out scientific basis to develop freshwater prawn culture in brackish water, in order to diversify culture systems and species, to stabilize social-economics for inhabitants, and to adapt to the issues of sea level rise and saltwater intrusion in Mekong Delta 1.2.2 Specific objectives - To analyze the status of freshwater prawn culture in brackish water in Mekong Delta To evaluate the effects of salinity on osmoregulation and biochemical parameters of prawn as well as reproductive and growth performances, survival rate, and productivity of freshwater prawn cultured in experimental tanks - To determine technical and financial efficiency of some freshwater prawn pond culture trials in brackish water area 1.3 Research activities Surveying the status of freshwater prawn in brackish water in Mekong Delta Comparing some bio-parameters, growth rate, and survival rate of freshwater prawn cultured in tank under different salinities Culturing freshwater prawn in small-scale farms in brackish water in Tra Vinh province 1.4 Research significance The research findings provide new knowledge on the effects of salinity on some biological characteristics of freshwater prawn under experimental conditions Besides, it also shows technical characteristics, the economic efficiency, and major factors that effect the productivities and financial efficiency of culture systems in different provinces in Mekong Delta The results of study strongly contribute to planning and developing strategies for freshwater prawn culture in brackish water in Mekong Delta The study is also an important reference for education and further researches on freshwater prawn as well as other species, that contributes to be scientific basis, technical and financial improvement in aquaculture production in brackish water area 1.5 New findings of the study From the results of the experiment, research, and survey on the real conditions, the studies all showed that freshwater prawns cultured in brackish water of 5-15‰ grow not differently compared to those in freshwater; moreover, decrease in spawning compared to those in freshwater The study updated, deeply analyzed and showed the development trend, technical and socio-economical aspects, and factors effecting to the efficiency of culture systems of freshwater prawn in brackish water area The study provide results of the trials in freshwater prawn culture in different salinities with technical supports resulting in better efficiency compared to the current status This is an important basis to improve and develop further culture system of freshwater prawn in brackish water in Mekong Delta Chapter MATERIALS AND METHODS 3.1 Approach Method The study was conducted based on approach basis as the follow: (i) Freshwater prawn was one of the importantly economic species; (ii) This species had wide range of distribution in freshwater and brackish water; (iii) freshwater prawn culture has been practiced in brackish water in Mekong Delta; (iv) Mekong Delta had large salinization area and tent to face with stronger saltwater intrusion in the next time due to impacts of climate change which need effective solutions, (v) Studying to find out suitable cultured species and aquaculture systems to adapt to climate change and saltwater intrusion require strong scientific knowledge and experiences 3.2 Research diagram Objective: To analyze status and to find out scientific information for culturing prawns in brackish water Survey and evaluation on the current status of culturing prawns in brackish water in Mekong Delta Experiment: Effect of different salinity on growth, physiology, biochemical, reproduction of prawns cultured in tanks Practice: Monitoring technical, environmental parameters, financial efficiency of culturing prawns in ponds at different salinity in brackish water System: Prawns + Rice culture alternativ ly with Tiger shrimp in field Pupulatio n culture of prawns in tanks at different salinity (0, 5, 10, 15‰) Prawn culturing at different sites in Tra Vinh Duyen Hai: ponds Cau Ngang: ponds Tra Cu: ponds System: Prawns culture alternativ ly with Tiger shrimp in pond Individual culture of prawn in tanks at different salinity (0, 5, 10, 15‰) Analyzing, Linking and discussion to evaluate the results Conclusion and recommendation Figure 3.1: Research diagram 3.3 Time and location The research has been carried out from 2010 to 2014 in Tra Vinh, Bac Lieu, and College of Aquaculture and Fisheries (Can Tho University) 3.4 Study Methods 3.4.1 Survey and evaluation of the status of freshwater prawn in brackish water in Mekong Delta The survey was carried out in 2013 with 60 farms in Bac Lieu and 48 farms in Tra Vinh Especially, in Tra Vinh, 16 farms are selected to survey in 2010 and re-survey in 2013 3.4.1.1 Secondary data collection Information and primary data were collected from annual reports of Department of Agriculture and Rural Development, Fisheries Division in Tra Vinh and Bac Lieu Collected information and data include statistics on culture area and production of freshwater prawn, advantages and disadvantages, and development plan 3.4.1.2 Primary data collection Primary data were collected through the interview of farmers which applied culture systems as follows, using questionnaires: - Freshwater prawn + Rice – Tiger shrimp system (System 1): Surveying 60 farms in Hong Dan and Phuoc Long districts, Bac Lieu province In this system, freshwater prawn was integrated with rice on rice field in rainy season after tiger shrimp crop in dry season - Freshwater prawn- Tiger shrimp (System 2): 16 and 48 farms were surveyed in 2010 and 2013, respectively in Cau Ngang, Tra Cu, and Duyen Hai districts (Tra Vinh province) - The content of the questionnaires: (i) general information of farms, (ii) technical aspects, (iii) economical aspects, (iv) advantages and disadvantages of farms during crop, (v) plan and suggestion 3.4.2 Evaluation of the effects of salinity on biological parameters, growth rate and survival rate of freshwater prawn in tank 3.4.2.1 Experimental design The experiment was conducted in treatments with different salinities including 0‰ (control), 5‰, 10‰ and 15‰ Each treatment was assigned to groups consisting of population and individual culture a) Population culture Objective: To evaluate the effect of salinity on growth, survival rate, biomass, physiological and biochemical parameters, breeding of freshwater prawn Prawns were kept in composite tanks (2m3) with density 60 individuals/tank Each treatment was triplicated Initial weight and length of prawn were 0.3-0.5g and 2.8-3.3 cm, respectively b) Individual culture Objective: To evaluate the effect of salinity on molting period, maturation, the first time of spawning, re-mature and spawning period of freshwater prawn Each individual was kept in net cage (15x15x75cm) with net mesh of 0.5mm Each treatment has 60 cages (60 prawns) placed in one composite tank (2m3) and with 50cm of water level Cages were numbered from to 60 3.4.2.2 Experimental conditions Freshwater prawn fingerlings were kept in freshwater in a month before carrying out experiment Healthy prawns without deformity and disease were selected and acclimated to salinity up to 5‰, 10‰, and 15‰ in accordance to each treatment Experimental system were placed under nylon roof and kept aerated continuously For population culture, nylon bunch were used as substrates for prawns to avoid cannibalism 3.4.2.3 Control and Management Experimental prawns were fed with commercial feed (Starter, UP) with crude protein at 35% In the first 60 days, prawns were fed times per day, then, twice per day (5-10% body weight/day) Feed were spread out for population culture and fed each cage for individual culture Exceed feed and waste were siphoned once per day (before feeding) Exchanging 50% of water once per weeks Culture period was 120 days 3.4.2.4 Collecting data a) Water quality in tanks Water quality parameters such as temperature, pH, TAN, N-NO2- and alkalinity were recorded daily b) Parameters on freshwater prawn - Population culture: taking sample once per month to determine growth parameters, survival rate, ratio of berried /not berried female, male/female ratio Biomass of prawn was calculated at the end of experiment + Biochemical parameters: At the end of the experiment, randomly sampling individuals/ tank to analyze some biochemical parameters such as protein, lipid, energy, carbohydrate, and minerals + Physiological parameters: sampling 0.2 mL of culture water and 0.1-0.2 mL of prawn blood (3 individuals/ tank) to measure osmotic pressure monthly from the 2nd month onwards After sampling blood, prawns were re-stocked for culture in tanks - Individual population: growth parameters and survival rate were sampled once per month Growth parameters such as body weight and length measured in each cage Molting period of each prawn was checked daily Determining ratio of male and female monthly from the 2nd month Mature, spawning and re-spawning were checked and recorded daily in each tank The quantity of re-mature and spawning of each prawn were also recorded c) Analysis method The biochemical parameters of prawn meat were analyzed by AOAC (2000) method Prawn meat samples were mashed and dried at 60oC during 48 hours, then grinded to analyze protein, lipid, carbohydrate, and minerals d) Analyzing concentration of osmotic pressure in water environment and prawn blood Osmotic pressures were measured by Osmotic Pressure Fiske One – Ten Osmometer 3.4.2 Experiment on culture of freshwater prawn in brackish water pond in rainy season (alternatively with tiger shrimp in dry season) in farms in Tra Vinh province 3.4.3.1 Some main parameters to choose experimental site The study was conducted in brackish water pond from June to December, 2013 Selected ponds must meet some important requirement 3.4.3.2 Choosing and preparing ponds Three ponds were chosen in each district of Duyen Hai, Cau Ngang, and Tra Cu, Tra Vinh province, to guide and to monitor on prawn culture Each pond is 4000 m2 in area and 1.5m in depth Pond preparation was carried out in June After harvesting tiger shrimp, ponds were drained off and were limed and dried for days Water was then supplied through filter bag and applied with Saponin to kill predators Prawns were stocked after one week 3.4.3.3 Stocking and management Freshwater prawn (PL15) (average weight 0.02g/ individual) sourced from hatchery are stocked at inds/m2, and fed with commercial feed (Starter, UP) with crude protein 35% Prawns were fed times per day with different feeding rates based on culture month: + 1st month: 15-10% prawn body weight + 2nd month: 10-5% prawn body weight + 3rd month: 5-3.5% prawn body weight + 4th month: 3.5-3% prawn body weight + 5th month: 3-2% prawn body weight No water exchange in the first month From the second month and onwards, 30% of pond water was exchanged twice per month 3.4.3.4 Collecting data a) Water quality parameters: Temperature, pH, Dissolved oxygen (DO), TAN, Nitrite and alkalinity were recorded weeks/time b) Parameters on prawns: Prawn weight, male and female ratio, egg carrying time, and ratio of berried female prawn were measured monthly Prawn yield (kg/ha/crop) was evaluated after harvesting Parameters on economic efficiency were calculated 3.4.3 Data analysis Data were checked, coded, input and analyzed using Excel Office 2003 and SPSS 16.0 Chapter RESULTS AND DISCUSSION 4.1 Status of prawn farming systems in brackish water in Mekong Delta 4.1.1 Giant fresh water prawn + rice culture (alternative black tiger shrimp) in Bac Lieu Province (M1) 4.1.1.1 Technical characteristics With low stocking density, simple techniques, simple feeding method and high production (110±52.7 kg/ha/crop), this system helps diversify products and the farmer’s income (Table 4.1 and Figure 4.1) Table 4.1 Technical characteristics of prawn- rice farming system1 Technical characteristic Farm structure Farm area Ditch ratio Ditch depth Water level on flatform Prawn stocking Prawn size at stocking Month of stocking Stocking density Monitoring Salinity Water exchange interval Amount of water exchange Feeding Unit Average Min- Max % m m 2.15±1.07 29.1±5.08 0.967±0.060 0.457±0.056 0.5-5.0 20.0-45.0 0.8-1.0 0.4-0.6 cm Lunar calendar inds/m2 1.26±0.105 1.1-1.5 5-7 0.2-4.0 1.05±0.602 ‰ 5.22±1.87 2.0-10.0 days 18.3±6.23 15.0-30.0 %/time 28.0±6.84 20.0-50.0 No feeding or only supplementation Harvest Culture period Size at harvesting Total production Month 7.18±1.11 G/inds 47.9±10.9 kg/househol 235±113 d/crop Productivity kg/ha/crop 110±52.7 Survival rate % 18.5±8.38 Note: all the data was shown Mean value± standard deviation Month Black tiger shrimp Giant fresh water prawn Rice 6.0-8.0 31.2-71.4 100-600 50-300 4.9-40.0 10 11 12 Fig 4.1 Cropping seasons of the prawn-rice-shrimp farming system 4.1.1.2 Economical efficiency of giant fresh water prawn + rice - tiger shrimp (M1) In this system, production cost and gross income of shrimp and rice was higher than prawn However, the B/C ratio of these crops were lower than that of prawn (Table 4.2) With 50.9 million/ha/year in total net income, tiger shrimp, rice and prawn accounted for 44.9% 32.4% and 22.7%, respectively This showed various products and the important role of prawn in this system Table 4.2: Economical efficiency of prawn-rice- shrimp farming system1 Criteria Giant Fresh Tiger shrimp Rice Total water prawn Unit (Million/household/year) Total 7.80±5.40 32.4±13.9 30.0±13.8 70.3±30.6 production cost (2.4-28.3) (10.0-70.0) (11.0-60.0) (27.2-158) Gross income 32±14.8 85.6±42.2 70.0±33.9 188±84.6 (12-67.5) (30.0-200) (24.0-150) (75.0-405) Net income 24.4±11.5 53.1±28.9 40.0±20.3 118±54.8 (8.10-54.1) (20.0-130) (13.0-90.0) (44.1-266) Unit (Million/ha/year) Total 3.50±2.30 14.2±2.90 12.6±0.982 30.5±4.8 production cost (0.71-13.1) (10.0-25.0) (10.0-16.6) (23.7-47.10) Gross income 15.1±8.40 37.1±8.50 29.1±1.60 81.4±14.6 (6.00-51.0) (22.8-60.0) (23.7-36.6) (61.7-131) Net income 11.5±6.80 22.8±6.10 16.5±1.40 50.9±10.6 (3.10-37.9) (12.5-36.6) (12.5-20.0) (33.7-90.0) B/C (%) 390±206 160±28 130±15 170±20 (60-790) (100-200) (100-180) (120-260) Note: All the data shows mean value± standard deviation (min- max) 4.1.1.3 Regression analysis in the influence of technical factors to the efficiency of the system1 Prawn yield (Y, kg/ha) in the system is effected significantly with factors, including X1: Years of culture experience (years), X2: stocking density (inds/m2); X3: culture period (months); X4: survival rate (%); X5: harvesting size of prawn (g) Regression is showed as the follow: Y = -99,37+ X1 +68 X2 - 2X3 + 4,0 X4+1,2 X5 (1) (R= 0,85; R2= 0,72; P=0,00) Net income (1000VND/ha/crop) in the system is effected significantly with factors, including: Y = 545 X1 + X2+ 958 X3 - 2.301 X4 + 132 X5 + 1.923 (R= 0,62; R2= 0,4; P=0,00) Where: Y1: Net income (1000VND/ha);X1: Time of experience (Years);X2: Stocking density (inds/m2); X3: Supplementary feeding ;X4: Culture period (months);X5: seling price (1000VND/kg) i) Effect of salinity on efficiency of prawn-rice-shrimp farming system The study indicated the potential of culturing fresh water prawn in brackish water with 10‰ of salinity (Table 4.3) Table 4.3: Effects of salinity on technical factors and the efficiency of prawn-rice-shrimp farming system1 Criteria Average salinity to 5‰ > to 10‰ (n=37) (n=23) Time for stocking (lunar calendar month) 6.0±0.1a 6.4±0.2b a Size of postlarvae (cm) 1.23±0.02 1.28±0.02a b Culture period (Months) 7.7±0.548 6.8±0.902a a Prawn size at harvesting (g) 48.5±11.7 47.1±9.69a a Survival rate (%) 18.7±8.56 18.2±8.28a a Yield (kg/ha/Crop) 117±50.6 99.7±55.5a a Total production cost (Million VND/ha/crop) 4.00±2.00 2.80±2.64a a Total gross income (million VND/ha/crop) 16.3±7.80 13.3±9.00a a Net income (million VND/ha/crop) 12.2±6.70 10.4±6.80a a B/C ratio (%) 340±162 470±244b Note: Values in the same row with the same superscript are not significantly different (p>0.05) Correction between salinity and ratio of Benefic/cost as the following equation: y = 3.26 Ln(x) - 1.11 (r2 = 0.37; p=0.00) (Fig 4.2) B/C ratio %) Salinity (%o) Fig 4.2: Corelation between salinity and B/C ratio ii) Effects of other factors to efficiency of prawn culture in the systems1 Besides above technical factors, effects of other factors on production efficiency are presented in Table 4.4 Nursing is one of the key factors contributing to improvement of yield and profit although the difference was not statistically significant (p> 0.05), but B/C ratio was significantly higher (p 0.05) In summary, the prawn -rice –shrimp farming system on the field helped in improving income, maintaining and developing rice farming, contributing to food security, and environmental protection 4.1.2 Status of semi-intensive prawn culture in ponds alternatively with shrimp in Tra Vinh (Prawn- shrimp farming system) (MH2) The combination of prawn farming in this model contributes to diversifying the cultured species, reducing over development of tiger shrimp, minimizing the risk of disease pathogen spread of shrimp farming, minimizing risk in income loss, and promoting the farming in the future Information on technical and financial performance of the system is presented in Figure 4.3; Table 4.6 and Table 4.7 Month 10 11 12 Tiger shrimp Giant fresh water prawn Fig 4.3 Cropping seasons of the prawn-shrimp farming system Table 4.6: Technical characteristics of semi-intensive prawn culture (alternative with tiger shrimp) Technical characteristics Unit Average Min-Max Pond Pond area 0.6±0.588 0.2-4.2 Pond depth M 1.32±0.108 1.0-1.5 Liming kg/ha 39.3±4.9 0-125 Prawn stocking Size of post larvae Cm 1.21±0.068 1.1-1.5 Month of stocking Lunar calendar 4-8 Stocking density Inds./m2 8.97±3.58 2.8-15.6 Management Feeding Commercial feed combined with homemade food and trash fish Water salinity ‰ 5.0±2.19 1.0-10.0 Water exchange Time/day 20.1±7.20 15-30 Water exchange rate %/time 27.4±7.47 10-50 Culture period Months 5.6±0.7 3-6 Harvest Prawn size at harvest G 34.9±9.23 18.2-58.8 Production kg/crop/household 594±474 100-2.500 Yield kg / / crop 886±642 125-2.812 Survival rate % 28.2±14.6 4.0-58.8 All the data was shown as average value± standard deviation (min- max) Table 4.7: Economical efficiency of prawn-rice-shrimp farming system Criteria Freshwater prawn Tiger shrimp Total Unit (million / household / year) Production 40,6±31.5 91.0±90.8 138±96.7 cost (4.60-151) (3.50-300) (21.3-353) Gross income 82.5±69.5 144±16.0 226±185 (14.0-330) (0-600) (17.0-660) Net income 42.0±51.5 53.0±77.4 95.0±103 (106-197) (8.00-300) (156-328) Unit (million / / year) Production 59.4±37.1 149±158 208±164 cost (18.0-176) (5.6-667) (26.6-735) Gross income 127±104 234±271 362±309 (21.3-478) (0-1.040) (23.1-1.300) Net income 68.0±86.9 86.0±12.8 154±174 (152-393) (0,10-440) (223-611) B/C ratio (%) 120±100 40±80 70±60 (90-460) (100-230) (90-260) All the data was shown as mean value± standard deviation (min- max) I) Multiple regression analysis of the influence of technical factors to effectively of prawn culture systems Yield and profit of prawn farming systems in Tra Vinh province depended on many factors as the following equation: - Factors effecting prawn yield Y= 25 X1 + 103 X + 2,7 X3 + 31 X4 + 31 X5 - 2.151 (1) ( R= 0,94; R2=0,88; p=0,00) (1) Where: Y1: Yield (kg/ha) X1: Time of experience (years); X2: Stocking density (ind/m2); X3: Culture period (months); X4: Survival rate (%); X5: Harvesting size (g) - Factors effecting net income Y2 = 11.489 X1 + 10.967 X2 - 2.627 X3 - 248 X4 + 36.052 X5 + 332 X6 + 3.751 X7 - X8 + 120.186 (2) (R2=0,558; R = 0,747; P=0,00) Where: Y1: Net income (1000VND/ha/crop);X1: Time of experience (Years);X2: Stocking density (inds/m2); X3: Seed price (VND/postlarve) ;X4: Lime using (kg/ha);X5: Culture period (months); X6: Seling price (1000VND/kg); X7: Harvesting size (g); X8:chemiscal using (kg/ha) ii)The impact of farming region on productivity and financial efficiency There is difference between farming regions in environmental conditions, technical and financial performance, although in many cases, the difference was not statistically significant (p> 0.05) (Table 4.8) Table 4.8: The impact of farming areas on the efficiency of prawn farming system2 Tra Cu Duyen Hai Criteria (n=16) (n=22) Pond area (ha) 0,619±0,306a 0,655±0,834a Density (ind/m2) 9,37±2,41a 8,25±4,07a o b Average salinity ( /oo) 7,17±1,45 3,77±1,47a b Culture period (month) 5,72±0,407 5,64±0,743ab a Size of prawn (g /ind) 35,8±7,45 36,3±9,38a a Survival rate (%) 30,5±13,6 23,8±13,1a Yield (kg / / crop) 1.000±634a 732±724a a Total cost (million VND / / crop) 57,9±29,4 51,7±36,5a a Total gross income (million VND / / crop) 144±103 108±120a Cau Ngang (n=10) 0,430±0,1a 11,1±4,50a 3,50±1,52a 5,20±0,919a 30,9±11,4a 34,3±18,0a 937±441a 78,7±45,7a 144±61,3a Profit (million VND / / crop) Profit index (%) Percentage of households with profit(%) 86,0±80,2a 145±84,9a 100 56,0±94,2a 90,1±109a 86,4 65,0±84,0a 128±97,4a 80,0 Percentage of households with losses (%) 13,6 20,0 Values in the same column with the same superscript are not significantly different (p>0.05) 4.1.2.5 Comparison of technical and financial aspects of prawn farming system in 2010 and 2013 (system2) There is no significant difference in technological factors of prawn farming in 2010 and 2013, which requires further research to study, innovate and apply technology for prawn farming region, improved the income of farmers Table 4.9: Technical factors prawn farming in 2010 and 2013 (system2) Technical Information Unit 2010 2013 The total area Ha 0,731±0,512a 0,744±0,450a a Pond area 0,350±0,141 0,453±0,247a a Lime using kg/ha 24,4±5,12 46,4±28,6b a Water depth m 1,1±0,020 1,2±0,12a a Stocking time Lunar calendar 5-8 5-8a a Stocking density Ind/m 4,8±1,53 7,8±3,89b a Stocking salinity ‰ 4,3±2,17 5,0±2,87a Culture period Month 6 Size of harvest prawn g/Ind 40,5±8,60a 37,9±9,12a a Yield kg / / crop 847±370 854±702a Values in the same column with the same superscript are not significantly different (p>0.05) In summary, the rotational freshwater prawn-tiger shrimp farming systems can be applied in high salinity regions (up to ‰ or higher), where is impossible to cultivate rice crop The culturing freshwater prawn in the rainy season could help to avoid breaking out of diseases because there is no continuous culture of a special species, and also avoid wasting ponds in case of prawn culture was only conducted in the dry season The results showed that further studies need to be carried out for technical innovation and the stability of the prawn farming system 10 4.2 Study on the effect of different salinities on biological parameters of prawns culturing in tanks 4.2.2 Effects of different salinities on biological parameters of prawns culturing in population 4.2.2.1 The survival rate of prawns after 120 days of culture The lowest survival rate of prawns was recorded in the control treatment at 0‰ of salinity, the highest survival rate was showed in treatments at 10‰ of salinity, and there were significantly different between treatments (p 0.05) (Table 4.10 and Table 4.11) Table 4.10 The growth rate of prawn in weight after 120 days of culture Treatments 0‰ 5‰ Initial weight (g) 0.34±0.02 0.34±0.02 Final weight (g) 14.94±1.25a 14.15±1.29a DWG (g/day) 0.122±0.010a 0.115±0.011a SGR (%/day) 2.96±0.09a 2.88±0.10a 10‰ 0.34±0.02 13.79±1.23a 0.112±0.010a 2.85±0.10a 15‰ 0.34±0.02 12.93±1.15a 0.105±0.010a 2.82±0.09a Notes: The average value ± standard error The mean values in the same column with the same superscript were not statistically significant differences (p >0.05.) Table 4.11 The growth rate of prawn in length after 120 days of culture Treatments Initial length (cm) Final (cm) 0‰ 2.52±0.05 5‰ 10‰ length DLG (cm/day) SGR_L (%/day) 8.00±0.24a 0.046±0.002a 0.94±0.03a 2.52±0.05 7.85±0.23a 0.044±0.002a 0.93±0.03a 2.52±0.05 8.17±0.24a 0.044±0.002a 0.92±0.03a 15‰ 2.52±0.05 7.73±0.22a 0.043±0.002a 0.91±0.02a Note: Values in the table were mean ± standard error The mean values in the same column with the same superscript were not statistically significant differences (p >0.05.) 4.2.4 Reproductive parameters of giant freshwater prawn 4.2.4.1 The percentage of ovigerous female The percentage of ovigerous female resulted in the highest percentage at 0‰ and lowest at 10‰ of salinity The prawn spawning in high salinity condition (10-15‰ of salinity) slowly occurred and showed lower fecundity compared to lower salinity condition (0-5‰ of salinity) (Figure 4.4) (%) trứngratio tôm mang Tỉ lệ berried Egg prawn (%) 100 80 60 a 0‰ 5‰ 10‰ 15‰ a a a a 40 a b 20 a b a 30 60 90 120 Thời gian (ngày) Culture periodnuôi (days) Figure 4.4: Percentage of egg berried female during culture period 11 4.2.5 Fecundity of prawns The treatment at 10-15‰ of salinity showed a slower spawning and lower fecundity; the absolute and relatively fecundity at 10-15% were lower than treatments at 0-5‰ of salinity The results were very important to brackish water prawn culture It helped to reduce the early maturation of prawns, improve growth rate, yield, prawn quality and financial efficiency in the system (Table 4.12) Table 4.12 Fecundity of prawns cultured at different salinities Reproductive parameter Weight of berried prawn (g) Absolute fecundity (Number Relative fecundity of eggs/berried prawn) (Number of eggs/g) After 60 days of culture 0‰ 5‰ 9.03 8.400 930 10‰ 7.44±0.25 2.940±255 395±21.2 15‰ After 90 days of culture 0‰ 12.6±2.81a 16.154±6.440a a 5‰ 11.7±2.56 17.043±6.302a 10‰ 11.2±2.08a 10.747±5.002b a 15‰ 14.3±0.49 16.360±2.885a After 120 days of culture 0‰ 14.9±2.64a 19.347±6.116a a 5‰ 13.5±3.08 21.920±7.542a a 10‰ 13.0±3.81 8.875±3.343b 15‰ 13.5±2.09a 10.567±4.426b Note: The values were shown in the table were mean and standard deviations The mean same superscript were not statistically significant differences (p >0.05.) (-): No ovigerous prawns 1.256±360a 1.419±360a 929±342b 1.159±181ab 1.328±442a 1.604±442a 909±242b 769±264b values in the same column with the 4.2.6 Biochemical composition of prawn meat after 120 days of culture The protein content of prawn meat showed the highest level at 5‰ treatment, and it’s significantly different compared to other treatments The results showed that prawn culturing in high salinity up to 15‰ did not affect on the quality of prawns (Table 4:13) Table 4.13 Biochemical composition of prawn meat at different salinities Treatments 0‰ 5‰ 10‰ 15‰ Moisture (%) protein(%) 70.6±0.82a 16.0±0.10a 68.7±0.61a 17.8±0.31b 69.0±0.76a 17.1±0.29ab 71.1±0.89a 16.1±0.28a Ash(%) 5.80±0.77a 5.53±0.58a 5.47±0.49a 5.18±1.00a Fat (%) 3.05±0.22a 3.76±0.41a 3.61±0.26a 2.84±0.34a Carbohydrate (%) 4.57 4.20 4.80 4.80 Energy (kJ/g) 21.7±0.08 a 22.6±0.24 a 23.9±0.19 a 23.6±0.15a Note: The values were shown in the table are mean and standard deviations The mean values in the same row with the same superscript were not significantly different (p >0.05) 4.2.7 Characteristics of blood physiology (Osmotic Pressure-OM) of prawns At treatments 0-15‰ of salinity, prawns were in hypertonic osmotic pressure condition, especially in treatments with salinity from 0-10‰ because of high OM disparity (Table 4:14) 12 Table 4.14 Osmotic Pressure of prawn blood at different salinities Treatments Water sample After 60 days After 90 days 0‰ 3.00±4.71a 463±33.0a 5‰ 228±91.2b 458±53.5a 10‰ 311±57.1b 468±74.2a 15‰ 424±152c 439±49.3a 464±28.5a 466±35.5a 459±31.7a 474±20.5a a ab c After 120 days 421±35.0 450±37.2 514±27.8 465±63.9bc Note: The values were shown in the table were mean and standard deviations The mean values in the same row with the same superscript were not statistically significant differences (p >0.05.) In conclusion, the results of culturing prawns in tanks with different salinities (0, 5, 10 and 15‰) were not statistically significant (p>0.05) in growth rate, biomass, biochemical and physiological parameters However, the survival rate of prawns in brackish water was higher than freshwater culture, the protein of prawn muscle at 5-10‰ was higher than 0‰ Especially, in brackish water, prawn maturation was slower, absolute and relatively fecundity were lower than freshwater culture 4.3 The effects of salinity on growth rate, molting, reproduction and survival rate of giant freshwater prawn in individual culture 4.3.1 Prawn molting Among treatments, the molting cycle of prawn at 0‰ of salinity was shorter than others, especially in the first five cycle However, no significant difference was recorded at the end of experiments The 0‰ treatment showed the highest number of molting cycle (10 cycles) and molting duration was ranged from 7.7-21.2 days At 5‰, 10‰, 15‰, the number of molting cycle were 8-9, with 8.9-23.4 days of molting duration (Figure 4.5) Số ngày lần lột xác (ngày) Days of molting duration (days) 35 0‰ 5‰ 10‰ 15‰ 30 25 20 15 10 5 10 Lần lột xác (lần) The number of molting cycles (cycle) Figure 4.5: Molting cycle of prawns during culture period between treatments 4.3.2 Percentage of egg berried prawn In low salinity condition, the prawn showed early maturation and high fecundity Especially, at 15‰, there was no record for ovigerous prawn after 120 days of culture The result showed that salinity has an effect on prawn maturation in individual culture model (Figure 4.6), also indicated the potential application of commercial brackish water prawn culture because of reducing early maturation and increasing growth rate 56,3 Tỷ lệ tôm mang trứng (%) Ratio of egg berried prawn (%) 60 50,0 0‰ 5‰ 10‰ 15‰ 50 40 30 48,5 39,4 29,6 25,9 20 10 3,1 6,1 30 60 90 120 gian nuôi (ngày) Culture periodThời (days) Figure 4.6: Percentage of egg berried females during culture period 13 4.3.3 Spawning cycle and fecundity of prawn The salinity at 0, 5, 10 and 15‰ had effects on the percentage of ovigerous females, spawning cycle and fecundity In high salinity condition, prawn showed low spawning, prolong re-matured cycle and reproduction, low fecundity compared to freshwater treatment (Figure 4.15) The results showed that brackish water prawn culture could get more benefits, especially in Mekong Delta where is abundant in brackish water areas From the results of the population and individual prawn culture, there are required further experiments in brackish ponds husbandry to access more detail efficiency Table 4.15: Spawning cycle and fecundity of prawn after 120 days of culture Salinity Number of (*) Berried female (‰) spawning Spawning ((ind) time (day) 10 Weight of berried prawn (g) Absolute fecundity (Number Relative fecundity of eggs/berried prawn (Number of eggs/g) 98±16 24 8.55±2.01 3.180±1.397 367±143 24±6 14 9.50±2.08 4.107±1.499 429±135 16±11 - - 12.4±0.09 - 5.640±984 - 456±83 - 86±17 21 9.97±3.13 4.080±1.352 410±83 25±11 12 11.5±3.72 4.573±1.679 401±103 24±1 12.4±1.57 4.339±876 347±39 25±4 13.6±0.23 5.040±136 371±14 108±20 12 8.73±2.65 3.006±1159 339±58 30±12 10.6±1.61 3.616±436 342±24 25±0 - - 13,7 - 5.136 - 375 - 15 Note: (*) The first spawning and next spawning cycle (day); Values in the table were mean and standard deviation, and (-) means no ovigerous prawn 4.4 The practice of culturing prawn in pond in Tra Vinh 4.4.1 Salinity in culture ponds in Tra Vinh Ponds in Cau Ngang were recorded with the lowest salinity (3.36‰) followed by Tra Cu (4.14‰) and Duyen Hai showed the highest salinity at 6.33 ‰ Most of surveyed ponds were stocked prawn year round, except Tra Cu, after 150 days of culture the salinity was dropped down to 0‰ (Figure 4.7) During culture period, temperature, pH, alkalinity, dissolved oxygen, TAN and nitrite were in acceptable range for the growth of prawns 12 Cầu Ngang Trà Cú Duyên Hải Độ mặn (‰) Salinity (‰) 10 15 30 45 60 75 90 105 120 135 150 165 180 Thời gian nuôi (ngày) Culture period (days) Figure 4.7: Variation of salinity in cultured ponds at different sites 14 4.4.2 Growth of prawn cultured in ponds Within studied salinity range, in high salinity condition, the prawn showed higher growth rates and bigger size compared to low salinity condition (Table 4.16) The salinity in pond at different sites could be the most important factor affecting to growth rate and productivity of prawn Figure 4.8 depicts the high correlation between salinity and productivity Table 4.16: The growth rate of prawn after 180 days of culture Site Wi (g/ind) Wf (g/ind) DWG (g/day) SGR (%/day) Cau Ngang 0.02 26.5±9.27a 0.15±0.01a 3.99±0.03a b b Tra Cu 0.02 36.1±15.80 0.20±0.01 4.16±0.02b b c Duyen Hai 0.02 39.5±15.71 0.22±0.01 4.21±0.03b Note: Wi: Initial weight of prawn, Wf: final weight of prawn when harvest Value in the table were mean and standard deviation The mean values in the same column with the same superscript were not statistically significant differences (p >0.05.) Khối lượng tôm (g/con) Body weight (g) 45 40 35 0,5289 y = 15,253x R = 0,6817 (p=0,006) 30 25 20 Độ mặn (ppt) Salinity (‰) Figure 4.8: Correlation between salinity and prawn weight after 180 days of culture 4.4.3 Percentage of egg berried prawn: (%) prawn berried of eggof RatioRatio (%) prawn berried The percentage of ovigerous prawn has followed the results from tank experiments as lower percentages of ovigerous females in higher salinity condition (Figure 4.10) Culture Culture periodperiod (days)(days) Figure 4.10: Percentage of ovigerous prawn in cultured ponds Note: Superscript (a, b) at the same day of culture indicate the significant differences (p0.05) Table 4.18: Financial efficiency of prawn at different districts in Tra Vinh Site Cau Ngang Duyen Hai Tra Cu Total cost (million VND /ha) 93.7±2.70a 98.4±3.50a 96.6±1.8a a b Total income (million VND 168±5.60 254±9.70 /ha) 295±15.3c a b Profit (VND million/ha) 74.2±4.50 156±10.6 199±17.0c a b Profit index (%) 79.2±4.90a 158±13.7 206±27.6c Note: Values in the table were mean and standard deviation The mean values in the same row with the same superscript were not statistically significant differences (p >0.05.) Feed cost accounted the highest percentage, followed by labor cost because culture period was conducted for months, and seed cost is the next (Table 4.19) Table 4.1: Cost ratio of prawn cultured in ponds at different sites Cost ratio (%) Lime, drug chemical Seed Feed Labor Others and Cau Ngang 1.87 Tra Cu 1.78 Duyen Hai 1.81 17.2 60.4 19.2 1.33 16.4 62.3 18.3 1.27 16.7 61.6 18.6 1.29 16 Chapter CONCLUSIONS - RECOMMENDATION Conclusion The surveyed results in Bac Lieu and Tra Vinh showed that prawn culture accounted a small index in the total cost of the whole system, but it resulted in a good income index contributing to improving total income The high financial efficiency of prawn culture is an important platform to promote and develop this system There were several advantages from brackish water prawn culture such as less diseases, suitable water environment, easy feeding beside some difficulties, especially quantity and quality of seed supply The results of survey, experiments, and husbandry practice of prawn culture with different salinities in different sites have showed that there was no significant difference in growth rates between brackish (5 - 15‰) and freshwater culture (p>0,05) The results from prawn culture in tanks and husbandry practice in ponds showed slow maturation, spawning, re-mature and low fecundity in high salinity condition compared to freshwater culture In brackish water environment, survival rate and biomass of prawn after 120 days of culture were not significantly different (p>0.05) At the same size, brackish water prawn showed the higher weight than fresh water prawn Protein of prawn muscle at 5% of salinity was greater than others Semi-intensive prawn culture in ponds resulted that the growth rate, productivity, and financial efficiency in high salinity condition are higher than low salinity 17 Recommendations Continue to complete the technology of prawn culture in monoculture, integrated or polyculture with other species in different regions and salt intrusion level Study to produce prawn seed in the rainy season to ensure sufficiently supply for farmers, especially from May to July Lunar calendar More detail access on prawn quality in different salinity environments in ponds to develop the commercial brand Find solutions for prawn consumption, processing, exporting when conducting on a large scale 18 LIST OF PUBLISHED PAPERS Huynh Kim Huong, Lai Phuoc Son, Le Quoc Viet, Do Thi Thanh Huong, Tran Ngoc Hai, 2015 The effect of salinities on molting cycle, spawning and growth of giant freshwater prawn (Macrobrachium rosenbergii) Journal of Science, Can Tho University, Vol 38: page 35-43 Huynh Kim Huong, Le Quoc Viet, Do Thi Thanh Huong, Tran Ngoc Hai, Trials on prawn (Macrobrachium rosenbergii) culture in brackish water area of Trà Vinh province Science and Technology Journal of Agricultural and Rural Development, Vol 13, page 91- 97 Huynh Kim Huong, Le Quoc Viet, Do Thi Thanh Huong, Tran Ngoc Hai Analysis technical and financial aspects of prawn-rice rotational system in brackish water area in Bac Lieu This journal was accepted by Journal of Science, Can Tho Univesity 19