THAILAND RESEARCH

Objectives
1. To assess the relationship between aerobic and anaerobic pond bottoms in terms of organic matter decomposition and nutrient release.
2. To determine the effectiveness of common carp in removing organic matter from pond sediments and in recycling nutrients for tilapia ponds.
3. To evaluate physical and chemical conditions during microbial decomposition of organic matter and the resultant nutrient release during pond drying.

Significance
Accumulation of organic matter in pond soils during the grow out cycle causes severe oxygen depletion at the sediment-water interface (Boyd 1990). Under anoxic conditions, organic compounds are often decomposed to H2S, NH3 and CH4 which are harmful or even lethal to fish. It is of primary importance to prevent such situations in fish ponds. Two methods commonly practiced by fish farmers are: (1) polyculture with detritivorous fish (Lin 1982) and (2) pond drying between cycles of production (Boyd 1990). Detritivores consume organic matter, but also disturb sediments while feeding, which may increase turbidity and reduce water quality (Pillay 1992). The drying process enhances oxidation of organic material as well as nutrient regeneration in pond soils, and also allows photo oxidation and microbial decomposition of organic matter (Fast 1986). All of these processes should enhance nutrient recycling in ponds.

Anticipated Benefits
The results generated in this study will link bottom soil characteristics and management techniques. The use of polyculture to mitigate the accumulation of organic material on pond bottoms is a common practice throughout Asia, but has been little studied. Pond drying is also a common practice. Both have strong likelihood of improving pond bottoms and therefore production of fish in ponds.

Identification of Beneficiaries
Culturists throughout southeast Asia and other tropical countries where pond bottoms commonly become anoxic and heavily laden with organic matter.

Collaborative Arrangements
The Asian Institute of Technology will collaborate with these analyses. The facilities for such research include ponds at AIT. The University of Michigan will provide logistic and planning support for this project, and will be involved in the final data analysis and write up as well.

Experimental Design
Two experiments will be conducted to achieve the objectives.

Site: Asian Institute of Technology

Culture period: Pond experiment will be done over 150 days, including wet and dry seasons.

Experiment 1
2x2 factorial experiment in triplicate.

Treatment combinations: Aerobic or anaerobic pond bottom and tilapia alone or tilapia and common carp

	Treatment Aerobic bottom Anaerobic bottom Tilapia x x Tilapia + common carp x x

Stocking rates: Tilapia 2/m2 ; Common carp 3/10 m2

Water management: Water will be supplemented to maintain a depth of 1m.

Other inputs: Ponds will be fertilized with chicken manure at 1000 kg ha1 wk-1. Aerobic pond bottoms will be created by aeration.

Test Species: Nile tilapia, common carp.

Sampling plan: Measurements of water quality will be taken biweekly including standard PDA/CRSP water quality parameters (Egna et al. 1987). Fish growth will be measured on a monthly basis. Diel analyses will be done monthly. During the experiment, pond soil characteristics (N, P, organic matter and pH) will be measured at flooding, halfway through the experiment, and prior to draining. Pond bottom conditions (temperature, pH and dissolved oxygen) will be measured biweekly.

Experiment 2
Pond drying for one month.

Sampling plan: Pond bottom soil characteristics (N, P, organic matter, moisture and pH) will be measured immediately after draining. Weekly measurement of moisture, organic matter and pH will be done over the month long drying period. Ponds will be flooded after a month of drying and soluble reactive phosphorus (SRP) and dissolved inorganic nitrogen (DIN) will be measured in pond water and source water.

Statistical methods and hypotheses: The null hypotheses are that each treatment will not result in appreciable differences in soil organic matter and fish growth; and that pond drying will not result in appreciable differences in organic matter compared to filled ponds. Significance differences will be tested using ANOVA and multiple regression.

Schedule/Time line:
Experiments will begin in 9/97 and complete in 2/98.

Final Report Submittal: Final reports will be completed with the 1997-98 annual report in Fall 1998.

References
Boyd, C.E. 1990. Water quality in ponds for aquaculture. Agriculture Experiment Station, Auburn University.

Egna, H.S., N. Brown, and M. Leslie. 1987. General references: site descriptions, material and methods for the global experiment. Pond Dynamics/Aquaculture Collaborative Research Data Reports, Volume 1. Oregon State University, Corvallis, Oregon. 84 p.

Fast, A.W. 1986. Pond production systems: water quality management practices. Pages 141-168 in J.E. Lannan, R.O. Smitherman, and G. Tchobanoglous, eds. Principles and practices of pond aquaculture. Oregon State University Press, Corvallis.

Lin, H.R. 1982. Polyculture system of fresh water fish in China. Canadian Journal of Fisheries and Aquatic Sciences 39:143-150.

Pillay, T.V.R. 1992. Aquaculture and the environment. Fishing Book News, London.