|PD/A CRSP Twentieth Annual Administrative Report
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Subcontract No. RD010E-11
University of Arizona, Tucson, Arizona
|Kevin Fitzsimmons||US Principal Investigator|
|Yang Yi||Host Country Principal Investigator|
|Potjanee Nadtirom||US Principal Investigator|
|Wanwisa Saelee||Undergraduate Student (Thailand; from March 2002)|
|Remedios Bolivar||Host Country Principal Investigator|
|Bong Bolivar||Host Country Principal Investigator|
|JunRey Sugue||Research Assistant|
|Wilfrido Contreras-Sánchez||Host Country Principal Investigator|
|Alejandro MacDonal Vera||Graduate Student (Mexico; CRSP funded)|
This subcontract was awarded funding to conduct the following Tenth Work Plan investigations:
Note: The schedules for 10NSR3C and 10NSR3E were modified. The revised schedules appear in the forthcoming Addendum to the Tenth Work Plan.
Latin America and Caribbean Stakeholders Meeting at Tegucigalpa, Honduras, 21 August 2001. (Fitzsimmons)
Sixth Central American Symposium on Aquaculture at Tegucigalpa, Honduras, 2224 August 2001. (Fitzsimmons)
Aquaculture America 2002 at San Diego, California, 2730 January 2002. (Fitzsimmons)
Asia Region Expert Panel meeting at Beijing, China, 23 April 2002. (Bolivar, Fitzsimmons)
The survey on tilapia-shrimp polyculture was conducted in Thailand and Vietnam from March through June 2002. The survey conducted in Thailand was to assess the current status of farmers practice of tilapia-shrimp polyculture, while the survey conducted in Vietnam was to find out why Vietnamese shrimp farmers do not grow tilapia in shrimp ponds. In twelve provinces of Thailand, 61 farmers who culture fish in their shrimp farms were selected and interviewed using a structured checklist and open-ended type of questionnaires. In the Mekong Delta of Vietnam, university researchers, local shrimp farmers association and local government fisheries staff, and shrimp farmers were interviewed.
Results showed that three versions of tilapia-shrimp polyculturenamely simultaneous, sequential, and crop rotation systemsare practiced by Thai shrimp farmers. Among all interviewed farmers, 42.6% use a simultaneous polyculture system, while percentages of farmers using sequential and crop rotation systems are 34.4 and 6.6%, respectively. The remaining 16.4% of farmers stock fish in reservoir ponds and use a monoculture system for shrimp. Among the farmers who adopt the simultaneous tilapia-shrimp polyculture system, 76.9% released tilapias directly into shrimp ponds, and 23.1% stocked tilapias in cages suspended in shrimp ponds. Tilapia-shrimp polyculture is practiced in a wide range of salinity levels from 0 to 30. Tilapias used in the polyculture include red tilapia (Oreochromis spp.), Nile tilapia (O. niloticus), and Mossambique tilapia (O. mossambicus).
The survey revealed that shrimp production and economic returns from the two simultaneous polyculture systems and in sequential polyculture systems were higher than those in their respective shrimp monoculture systems practiced before. Also shrimp production and economic returns from these polyculture systems were higher than those in the crop rotation polyculture system and in the currently practiced monoculture system. Many farmers responded that tilapia-shrimp polyculture could improve water quality in shrimp ponds, reduce diseases, and reduce the use of chemicals. In the direct style of tilapia-shrimp polyculture, about 40% farmers believed tilapias compete for feed with shrimp, while the remaining 60% were not aware of such feed competition. The major reasons given by Vietnamese shrimp farmers for not growing tilapia in shrimp ponds are that tilapia would compete with the costly shrimp feeds, water quality in shrimp ponds was good enough and there was no need to use tilapia to improve water quality due to low shrimp stocking density, and added tilapia might bring dissolved oxygen down thus adversely affecting shrimp growth.
It can be concluded from the survey that polyculture of shrimp with tilapias may provide an alternative approach for shrimp farming, which could ultimately lead to a more sustainable shrimp industry. However, further research is needed on the merits for converting from shrimp monoculture to polyculture with tilapia.
This study, consisting of two experiments, was conducted at the Asian Institute of Technology, Thailand for 65 days from 20 February to 23 May 2002. The first experiment investigated the growth performance of shrimp (Penaeus monodon) and Nile tilapia (Oreochromis niloticus), water quality, and nutrient budget in different stocking combinations of tilapia-shrimp polyculture, while the second experiment assessed different harvest draining techniques in terms of nutrients and solids discharged from effluent water.
The first experiment was conducted in nine 200-m2 earthen ponds. There were three treatments in triplicate: 1) shrimp stocked alone at 30 fish m-2 (T1); 2) shrimp stocked at 30 fish m-2 and Nile tilapia stocked at 0.25 fish m-2 (T2); 3) shrimp stocked at 30 fish m-2 and Nile tilapia stocked at 0.50 fish m-2 (T3). The treatments were randomly allocated to the experimental ponds. Three ponds each from one treatment of the first experiment were designed as a block, and the treatments were in triplicate each in one of three blocks. The second experiment was conducted in the same ponds used in the first experiment in a randomized complete block design. There were three treatments in the second experiment: (A) ponds were completely drained with a pump placed on pond bottom, and shrimp and Nile tilapia were collected from a harvesting pit; (B) ponds were drawn from top to 20 cm deep with a pump placed on pond bottom, and shrimp and Nile tilapia were harvested by seining three times, followed by complete draining and collection of the remaining shrimp and Nile tilapia from a harvesting pit; (C) ponds were drawn with a pump firstly from top to 50 cm, then to 20 cm, and finally to 0 cm through lowering a pump to the respective water depth, and shrimp and Nile tilapia were collected from a harvesting pit.
Growth performance of shrimp, including mean individual weight, total length, mean daily weight gain, and net and gross yields was not significantly different (P > 0.05) among all treatments. Although the feed conversion ratio of shrimp was not significantly different among all treatments (P > 0.05), shrimp monoculture had significantly lower feed input than tilapia-shrimp polyculture (P < 0.05). Growth and survival of Nile tilapia were not significantly different between the low- and high-density tilapia treatments (T2 and T3, respectively) (P > 0.05), while fish yields were significantly higher in the high-density tilapia treatment than in the low-density tilapia treatment (P < 0.05). Approximate nutrients recovered by shrimp and tilapia were 1,459.7, 1,793.1, and 1,784.0 g N and 204.9, 302.3, and 391.1 g P in T1, T2, and T3, respectively. Nutrients lost in sediment were 69.86, 48.81, and 61.69% of total nitrogen (TN) and 46.96, 40.46, and 29.96% of total phosphorus (TP) in T1, T2, and T3, respectively. Nutrients lost to the water column were less than 1% in all treatments. Salinity was 5 initially and decreased quickly to 0 within three weeks in all treatments. Overall mean values of all water quality parameters except total ammonia nitrogen (TAN) and soluble reactive phosphorus (SRP) were not significantly different among all treatments (P > 0.05), while the final values of all water quality parameters except Secchi disk visibility were also not significantly different among all treatments (P > 0.05). Final values of Secchi disk visibility were significantly greater in the tilapia-shrimp polyculture than in the shrimp monoculture (P < 0.05).
Concentrations of all measured effluent parameters except for TN in draining schemes A and C increased significantly with the decreased water depths (P < 0.05). Draining scheme B resulted in significantly lower concentration of total solids (TS) at all depths when compared with those in schemes A and C (P < 0.05). The concentrations of all measured effluent quality parameters except TN were significantly higher in the bottom water (20 to 0 cm depth) than in upper depths in all draining schemes (P < 0.05). For the weighted mean concentrations estimated from four depths, there were no significant differences in total volatile solids, total suspended solids, and TN among all draining schemes (P > 0.05). However, the weighted mean concentrations of TS were the lowest in draining scheme B, intermediate in draining scheme A, and highest in draining scheme C (P < 0.05), while the weighted mean concentrations of TP in draining schemes A and B were significantly lower than that in draining scheme C (P < 0.05).
All treatments resulted in positive net returns. The highest net return was achieved in the shrimp monoculture (US$41.09 200 m-2 crop), intermediate in the high-density tilapia treatment (US$15.65 200 m-2 crop), and lowest in the low-density tilapia treatment (US$35.09 200 m-2 crop). However, there were no significant differences in net returns among all treatments (P > 0.05).
The present study showed that tilapia-shrimp polyculture is feasible technically; however, it is not attractive economically. More research needs to be conducted to optimize feeding management in the tilapia-shrimp polyculture.
The majority of the Mexican shrimp farming industry is situated in northwest Mexico. However, shrimp aquaculture in Mexico is in crisis due to a mix of the depressed world shrimp market, and disease outbreaks causing decreased yields (Panorama Acuícola, 2002).
To determine the potential for tilapia-shrimp polyculture in the area, we are conducting surveys in the states of Sinaloa and Nayarit. We have visited 37 farms, which represent 18.5% of the total number of farms in the northwest. Twenty of those were closed because they produce shrimp only during one cycle.
The data collected showed that farm size ranged from 40 to 1,000 ha, and the production varied significantly from 1 to 2,400 t yr-1. Most farms work two cycles per year (January through June and July through December). However, three farms were reported to work one cycle only (January through June), and one farm claimed to be able to produce shrimp in three cycles per year. The density used to stock ponds varied form 5 to 40 shrimp m-2, but most farms used 12 to 20 shrimp m-2. The average weight of shrimp harvested in the farms surveyed was 16.9 g, ranging from 12 to 24 g. The size of the shrimp harvested was directly related to the density used to stock the ponds.
The main cause of low yields was the viral disease White Spot Syndrome, which accounted for 59% of the reported problems causing low production. Low yields due to disease outbreaks combined with a low world price for shrimp have made many operations unprofitable.
The results from the survey also show that 76% of the shrimp farms experienced production problems, and many of these farms are considering alternative aquaculture strategies as an opportunity to stabilize production. Tilapia culture in shrimp ponds is being considered by 53% of the farmers because tilapia can be raised during the rainy season when salinity is too low for shrimp culture. The two main constraints in Mexico for the development of tilapia culture in shrimp ponds are knowledge of the biotechnologies required for culture in seawater and supply of salinity-tolerant strains of tilapia. This is a unique opportunity to continue harnessing the strengths of the PD/A CRSPs expertise and aid the development of a sustainable aquaculture system that would both safeguard jobs and provide work to low-income fishermen in coastal areas.
The majority of the Mexican shrimp farming industry is situated in the northwest of Mexico. However, shrimp aquaculture in Mexico is in crisis due to both the depressed world shrimp market and disease outbreaks causing decreased yields. To determine the potential for shrimp-tilapia polyculture in the area, we are conducting surveys in the states of Sinaloa and Nayarit. So far we have surveyed 37 farms, which represent 18.5% of the total number of farms in the northwest. The data collected to date showed that the main cause of low yields was white spot syndrome, a viral disease, which accounted for 59% of the reported instances of low production. These low yields due to disease out-breaks combined with a globally low prices for shrimp have pushed many operations into a situation where they are no longer profitable. The results from the survey also show that 76% of the shrimp farms experienced production problems, and many of these farms are considering alternative aquaculture species as an opportunity to stabilize production. Tilapia culture in shrimp ponds is being considered by 53% of the farmers. The two main constraints in Mexico for the development of tilapia as an alternative species for culture in shrimp ponds are knowledge of the biotechnologies required for culture in seawater and supply of salinity-tolerant strains of tilapia. This is a unique opportunity to continue harnessing the strengths of the PD/A CRSPs expertise and aid the development of a sustainable aquaculture system that would both safeguard the jobs of many local inhabitants and provide work to low-income fishermen in coastal areas.
The majority of disease outbreaks have been observed during the rainy season (July to October). The rains cause large fluctuations in salinity, temperature, and turbidity. It is suspected that these environmental fluctuations stress the shrimp and trigger disease outbreaks. In the past couple of years, a number of farmers have operated for just one cycle, stocking at low densities after the rainy season (December to February) and harvesting before the start of the rainy season (May to July). This is a longer production cycle, and larger shrimp were harvested, giving good yields per hectare. Although this system enables these farms to continue operating, they are not fully utilizing the shrimp ponds, which are being abandoned for a part of the year. This results in a seasonal job market for many of the local people or even those who operate the social cooperative farms. It is considered that tilapia would be well-suited to culture during this part of the year when ponds are not being used. Lower salinities associated with the rain would favor tilapia culture. Tilapia and low densities of shrimp could be stocked at the start of the rainy season in lower salinities and cultured through to December for Christmas markets. The combination of one shrimp cycle and one cycle of tilapia-shrimp polyculture using the culture system developed in collaboration between researchers and industry in the PD/A CRSP project would help the social cooperatives operate throughout the year. This would give a higher financial return from the infrastructure and providing fuller employment for the cooperatives and other local people.
We will initiate an experiment during the next cycle (starting December or January) and will have results by the end of April.
Four provinces were surveyed, namely Pampanga, Pangasinan, Bulacan, and Negros Occidental. A total of 19 farmers were interviewed for this study. The most successful pro-vince in terms of applying tilapia-shrimp polyculture in a sustainable way is Negros Occidental.
Farmers in Negros Occidental have adopted a tilapia-shrimp polyculture system that utilizes hapa net pens stocked with tilapia and placed in the center of the pond. Shrimp are stocked outside the hapas, and paddlewheels circulate water, which carries wastes to the center where they are consumed by the fish. In addition, the reservoir pond at the head of the farm intake water supply is heavily stocked with tilapia. Farmers observed that the tilapia seem to maintain a favorable algae bloom in the system, encourage a beneficial bacterial community, and reduce the numbers of zooplankters. Farmers in Negros Occidental follow a technology called TIPS (Tilapia Integration to Prawn Culture System), which combines the techniques of crop rotation, biological pre-treatment using tilapia reservoirs, and polyculture. The TIPS technology appears to have reduced the incidence of disease in polyculture ponds more than in monoculture ponds.
One advantage of the farmers in Negros Occidental who are using the TIPS technology in the tilapia-shrimp polyculture is their access to a saline-tolerant hybrid of tilapia known as Jewel tilapia that makes it possible for farmers to rear the fish in brackish water along with the shrimp.
The consistency of results using the TIPS technology in the province of Negros Occidental has revived the enthusiasm of the prawn growers to verify the management strategies in their farms. Slowly, the industry is gaining back momentum after the white spot virus has caused low survival if not wiped out all of the shrimp stocks in the province.
Different practice of integration was observed in the three provinces in Luzon. Farmers typically use milkfish and shrimp in their polyculture. However, in general their idea of integration is not systematic. Farmers integrate species such as crab, tilapia, milkfish, and shrimp if these become available or if the farmer has the money to buy the fry or larvae. The management system is very extensive with very low feed and fertilizer input. Most of the time cultured species are dependent on natural food available in the ponds. Large ponds are used with little attention to pond management.
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