Development of suitable cropping calendars for tiger shrimp culture in the Mekong Delta, Vietnam | |
| Author | Vo Nam Son |
| Call Number | AIT Diss. no.AQ-11-04 |
| Subject(s) | Cropping systems--Vietnam--Mekong Delta Tiger shrimp--Vietnam--Mekong Delta Shrimp culture--Vietnam--Mekong Delta |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Aquaculture and Aquatic Resources Management. |
| Publisher | Asian Institute of Technology |
| Abstract | This research was conducted to develop appropriate cropping calendars and schedules for black tiger shrimp (Penaeus monodon) culture in Soctrang Province of Mekong Delta of Vietnam. The investigation was conducted from November 2006 to February 2008. Climatic, water quality parameters, technical and economic criteria were considered as the main determinants of shrimp culture cropping schedule. There were four studies. The first survey (Study 1) was conducted to evaluate shrimp seed quality variation in the local market, and to identify technical and economic characteristics of local shrimp nurseries and hatcheries. Data on shrimp seed batches in the market (n = 6,045) of Soctrang provincial fisheries department (ST DoF) were used to evaluate the extent of white spot syndrome virus (WSSV), monodon baculovirus virus (MBV) or yellow head virus (YHV) infections (2003-2007). Seven hatcheries and 40 randomly chosen nursing farms were surveyed to evaluate technical-economic aspects. The second survey (Study 2) was conducted to identify main effects of local weather conditions and water quality parameters on shrimp culture. Monthly average air temperature, rainfall, water evaporation rates were collected form secondary data. The monthly water quality parameters (transparency, temperature, salinity, pH, dissolved oxygen (DO) total ammonia nitrogen (TAN), total Kjeldahl (TKN), nitrite (N-NO2), nitrate (N-No3) total phosphorus (TP), total alkalinity (as CaCO3) total suspended solid (TSS), total volatile solid (TVS) and chlorophyll-a) of shrimp ponds and river systems were directly measured and got from records of Soctrang Fisheries department (ST-DoF). The third survey (Study 3) was conducted to evaluate technical and economic aspects of integrated rice-shrimp (rise-shrimp dry-crop group) and intensive shrimp culture systems (intensive shrimp dry-crop and wet crop groups). Randomly selected 40 shrimp farmers from each group (n=120) were interviewed to determine stocking density, shrimp yield, feed conversion ratio (FCR), total cost (TC), net income (NI) and the investment risks. Soil type, pH and elevation were used to identify suitable areas for black tiger shrimp culture and to evaluate the advantages of different cropping schedules (Study 4). The suitable areas were selected using a digital soil map of Research Institute of Aquaculture No.2. The result showed that total infection rate of shrimp seed batches was 35%, predominantly caused by WSSV (37%), MBV (19%) and YHV (4%). Pathogen free seed batches were relatively higher (52%) during the dry season than the wet season (42%). All measured water quality parameters were in a suitable range for shrimp culture. There were no significant differences of water quality parameters between the dry and wet crop, except salinity. Salinity of inlet water was less than 10 and 5 g L-1 during January to June and August to December, respectively. Farmers made no attempt to adjust pond water salinity into a suitable range for shrimp growth in the wet season. Farmers stocked shrimp at a rate of 6.6 post-larva (PL) m-2 and culture for 158 days in the rice-shrimp system. The average survival rate, gross yield, FCR and NI were 43.9%, 780 kg ha-1 crop-1, 2.3 and US$2,118 ha-1 crop-1, respectively. The average production cost was US$4.0 kg-1 and feed cost was the largest cost item that accounted for 61.3%. The percentage of net loss was about 20%. In the intensive system, Principal Component Analysis (PCA) showed that the seeding month and other technical and economic variables except farmer's experience did not highly load into component analysis. There were significant differences in availability of pathogen free shrimp seeds and water quality parameters of intensive shrimp farming between the dry and wet seasons. The average stocking density, survival rate, gross yield and net income of intensive shrimp culture were 17 PL m-2, 55%, 2,470 kg ha-1 crop-1 and US$6,768 ha-1 crop-1, respectively. Average production cost was US$3.4 kg-1 and the feed cost was 58% of the production cost. Although shrimp yield was not significantly different, survival rate was significantly higher during the dry season (59%) than the wet season (49%). The logistic regression showed that the probability of yield loss was 15.6 times higher in the wet season than in the dry one. A positive NI was in the farms operating in the dry season using new ponds and performing laboratory tests to screen pathogen contamination of shrimp seeds before stocking. The significant differences in the survival rate between the dry and wet seasons can be attributed ot low water salinity (<5 g L-1) in the wet crop (P<0.05). But the average farm gate shrimp price of the dry crop harvest in the early wet season (July-September) was lower (US$5.5 kg-1) than the wet-crop price (US$6.0 kg-1) harvest in the early dry season (January-February). There was no significant difference between net economic loss of farmer groups that tested seeds for WSSV, MBV and YHV and those who did not subject to any laboratory test (20% of farms) in rice-shrimp culture system. However, the average NI ratio of polymerase chain reaction (PCR) of laboratory tested seed group was relatively better than non-tested group. In the intensive system, PCR tested seed group had high NI (P<0.05) compared to non-PCR tested seed group. The percentage of net loss of PCR tested and non-tested seed groups were 13 and 29%, respectively. The salinity, percentage of pathogen free shrimp seed batches, and farm-gate price of shrimp were used as the criteria in the analytic hierarchy process (AHP) to elucidate the advantages of different cropping patterns. The soil type and soil pH were used to compose a suitable site map for shrimp pond. The areas dominated by sandy soil, acid sulfate soils with pH below 4 and low salinity (below 5 g L-1) were considered unsuitable for shrimp culture. The total suitable area with alluvial soil and optimum salinity for at least part of the year accounted for 130,843 ha. Sixty eight percent of this area is currently used for shrimp culture and the rest has the potential for future development. The areas with the salinity remained above 5 g L-1 for 5 to 7 and 7 to 9 months per year were found suitable for one crop and two crops a year, respectively. The composed AHP priority for shrimp culture during December to next May was higher than for the seeds stocked from June to November. Shrimp cultured in the wet season suffers from the disadvantages of low survival rate and high risk from shrimp viral diseases. The development of zonal based cropping calendar was proposed to overcome these disadvantages. |
| Year | 2011 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Aquaculture and Aquatic Resources Management (AQ) |
| Chairperson(s) | Yakupitiyage, Amararatne |
| Examination Committee(s) | Gallardo, Wenresti G.;Anal. Anil Kumar;Lin, Chang Kwei;Nguyen Thanh Phuong;Macintosh, Donald John |
| Scholarship Donor(s) | The Government of Vietnam |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2010 |