THAILAND RESEARCH

Effluents and Pollution Research 3 (9ER3)/Experiment

Note: The following work plan replaces that in the Ninth Work Planin full.

Objectives
1) To use effluents from intensive catfish ponds as nutrients for tilapia culture ponds, and thus to reduce effluent effects from catfish culture.
2) To gain extra fish production at low cost, making aquaculture more profitable to farmers.

Significance
Clarid catfish has been one of the most popularly cultured freshwater fish in Southeast Asia. The present annual production in Thailand is estimated to be 50,000 tonnes. As an air breather, catfish can be grown at extremely high density (100 fish m^-2) with standing crop in pond culture reaching as high as 100 tonnes ha^-1 (Areerat, 1987). The fish are mainly cultured intensively and fed with trashfish, chicken offal or pelleted feed, which generally causes poor water quality and heavy phytoplankton blooms throughout most of the growout period. To maintain the tolerable water quality for fish growth, pond water is exchanged at later stages of the culture cycle (which is 120 to 150 days). The effluents containing concentrated phytoplankton biomass and nutrient, are unsuitable to irrigate rice fields because unbalanced N:P ratios (high nitrogen content) cause rice to fail to fruit. Wastewater disposal from catfish ponds has become a serious problem, especially in the Northeast Thailand where surface waters are in short supply. Farmers often discharge the wastewater to adjacent rice fields, which are damaged by this input. To fully utilize the effluents, unproductive wetlands can be excavated for tilapia culture. Such diversification and integration are regarded as important practices to enhance aquaculture sustainability (Alder et al., 1996; Pillay, 1996).

The wastes from catfish cultured in cages have been shown to be effective for producing phytoplankton to support Nile tilapia culture in the same pond (Lin et al., 1990; Lin and Diana, 1995). Similarly, tilapia reared in cages, feeding on phytoplankton in intensive channel catfish ponds, were shown to improve pond water quality as well as produce an extra crop (Perschbacher, 1995).

Anticipated Benefits
The integrated recycle system will be able to produce tilapia using effluents from intensive catfish ponds, which otherwise would be a source of pollution to surface waters. Economically, the profit margin of catfish culture will be augmented with tilapia at minimal cost. This system will provide scientific information on mass balances of nutrients and optimization of biological productivity.

Research Design
Location:AIT campus, Bangkok.

Pond facility:7 earthen ponds of 200 m² size. One pond will be partitioned to three equal compartments by small mesh net for the control. Other six ponds will be partitioned to two compartments: 1/3 pond area (67 m²) for catfish and 2/3 pond area (133 m²) for tilapia.

Culture period:90 to 120 days until catfish reach 200 to 300 g size.

Stocking density:25 catfish m^-2; 2 tilapia m^-2.

Test species:Hybrid catfish (Clarias macrocephlusx C. gariepinus);Nile tilapia (Oreochromis niloticus).

Nutrient inputs:Pelleted feed for catfish, effluents recirculated to tilapia compartments; tilapia compartments will also be fertilized for the first month.

Water management:Pond water depth to be kept at 1 m; The water between catfish and tilapia compartments can exchange through the partitioning net. In artificial water circulation treatment, the water in catfish compartment will be continuously circulated by submersed pumps to tilapia compartment at a rate of one exchange per week. No artificial water circulation will be done in the first month.

Sampling schedule:Water quality parameters will be analyzed biweekly and diel samples monthly, following standard CRSP protocols. Partial budgets will be estimated to assess costs and value of fish.

Statistical design and analysis:The experimental treatments will include catfish alone (treatment A, control), catfish and tilapia without artificial water circulation (treatment B), and catfish and tilapia with artificial water circulation (treatment C). Each treatment will be conducted in triplicate. Ponds will be flooded and stocked with fish. Nutrient budgets will be determined.

Null hypothesis:Water exchange between catfish and tilapia compartments does not affect water quality and fish production.

Regional Integration
In the SE Asian region, both clarid catfish and tilapia are widely cultivated with traditional segregated pond culture systems. The integrated systems will be a new step in production technology that will promote efficient production as well as environmental sustainability.

Schedule
July to November 1999

Report Submission
March 2000

References
Adler, P.R., F. Takeda, D.M. Glenn, and S.T. Summerfelt, 1996. Enhancing aquaculture sustainability through utilizing byproducts. World Aquaculture, 27:24–26.

Areerat, S., 1987. Clarias culture in Thailand. Aquaculture, 63:355–362.

Lin, C.K. and J.S. Diana, 1995. Co-culture of catfish (Clarias macrocephalus x C. gariepinus) and tilapia (Oreochromis niloticus) in ponds. Aquatic Living Resources, 8:449–454.

Lin, C.K., K. Jaiyen, and V. Muthuwan, 1990. Integration of intensive and semi-intensive aquaculture: Concept and example. Thai Fisheries Gazette, 43:425–430.

Perschbacher, P.W., 1995. Algal management in intensive channel catfish production trials. World Aquaculture, 26:65–68.

Pillay, T.V.R., 1996. The challenges of sustainable aquaculture. World Aquaculture, 27:7–9.