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 ev
Trang 1MINISTRY 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
Trang 2THIS 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 2:
Examiner 3:
The disseratation is available in Libraries:
Learning Resource Center of Can Tho University
National Library, Vietnam
Trang 3Chapter 1 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
1 Surveying the status of freshwater prawn in brackish water in Mekong Delta
2 Comparing some bio-parameters, growth rate, and survival rate of freshwater prawn cultured in tank under different salinities
3 Culturing freshwater prawn in small-scale farms in brackish water in Tra Vinh province
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
Trang 4The 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 3 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
Trang 5Figure 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 2 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
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
System:
Prawns culture alternativ
ly with Tiger shrimp in pond
Individual culture of prawn in tanks at different salinity (0,
5, 10, 15‰)
Prawn culturing at different sites in Tra Vinh
Duyen Hai: 3 ponds Cau Ngang: 3 ponds Tra Cu: 3 ponds
Analyzing, Linking and discussion to evaluate the results
Conclusion and recommendation
Trang 6- 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
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 1 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 1 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 3 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 2 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
- 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
Trang 73.4.2 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 3 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 7 inds/m2, and fed with commercial feed (Starter, UP) with crude protein 35% Prawns were fed 4 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 2 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
Trang 8Chapter 4 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 Unit Average Min- Max
Prawn size at stocking cm 1.26±0.105 1.1-1.5
Month of stocking Lunar calendar 5-7
Stocking density inds/m2 1.05±0.602 0.2-4.0
Monitoring
Water exchange interval days 18.3±6.23 15.0-30.0
Amount of water exchange %/time 28.0±6.84 20.0-50.0
Feeding No feeding or only supplementation
Harvest
Culture period Month 7.18±1.11 6.0-8.0
Size at harvesting G/inds 47.9±10.9 31.2-71.4
Total production kg/househol
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
Trang 9Table 4.2: Economical efficiency of prawn-rice- shrimp farming system1
Criteria Giant Fresh
32.4±13.9 (10.0-70.0)
30.0±13.8 (11.0-60.0)
70.3±30.6 (27.2-158) Gross income 32±14.8
(12-67.5)
85.6±42.2 (30.0-200)
70.0±33.9 (24.0-150)
188±84.6 (75.0-405) Net income 24.4±11.5
(8.10-54.1)
53.1±28.9 (20.0-130)
40.0±20.3 (13.0-90.0)
118±54.8 (44.1-266)
Unit (Million/ha/year)
Total
production cost
3.50±2.30 (0.71-13.1)
14.2±2.90 (10.0-25.0)
12.6±0.982 (10.0-16.6)
30.5±4.8 (23.7-47.10) Gross income 15.1±8.40
(6.00-51.0)
37.1±8.50 (22.8-60.0)
29.1±1.60 (23.7-36.6)
81.4±14.6 (61.7-131) Net income 11.5±6.80
(3.10-37.9)
22.8±6.10 (12.5-36.6)
16.5±1.40 (12.5-20.0)
50.9±10.6 (33.7-90.0) B/C (%) 390±206
(60-790)
160±28 (100-200)
130±15 (100-180)
170±20 (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 5 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+ 3 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 5 factors, including:
Y = 545 X1 + 5 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
Culture period (Months) 7.7±0.548b 6.8±0.902a
Prawn size at harvesting (g) 48.5±11.7a 47.1±9.69a
Survival rate (%) 18.7±8.56a 18.2±8.28a
Yield (kg/ha/Crop) 117±50.6a 99.7±55.5a
Total production cost (Million VND/ha/crop) 4.00±2.00a 2.80±2.64a
Total gross income (million VND/ha/crop) 16.3±7.80a 13.3±9.00a
Net income (million VND/ha/crop) 12.2±6.70a 10.4±6.80a
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)
Trang 10Salinity (%o)
B/C ratio %)
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) Prawn culture supplemented with feed have significantly higher productivity and profits (p <0.05) compared with those without feeding (Table 4.5)
Table 4.4: Some technical factors affecting the productivity and economical efficiency of prawn culture of the prawn-rice-shrimp farming systems
Net income (1.000đ/ha/Cro p)
B/C ratio (%)
Values with the same superscript within the same column are not significantly different (p>0.05)
Table 4.5: Effects of culture period on the efficiency of the prawn culture in the prawn-rice-shrimp farming system
Criteria Culture period (months)
Survival rate (%) 23.0±1.9b 16.4±2.9a 17.3±1.4ab
Yield (kg / ha / crop) 95.1±9.3a 112±31.3a 115±7.4a
Production cost (million VND / ha) 1.79±0.197a 4.10±1.30b 4.16±0.320b
Gross income (million VND / ha) 12.1±1.08a 16.7±4.92a 11.8±1.07a
Net income (million VND / ha) 10.3±0.94a 12.6±3.69a 11.8±1.07a
B/C ratio (%) 60±0.5b 36±0.6a 31±1.2a