THAILAND RESEARCH

Objectives
To develop viable and practical techniques to reduce clay turbidity in aquaculture ponds in order to increase efficiency of pond fertilization.

Significance
Mud turbidity is a global problem in aquaculture using ponds with heavy clay dikes and bottoms. Colloidal clay particles from the dikes and bottoms (as well as from runoff and source water) suspend in the water column and inhibit plankton growth by binding with mineral nutrients from the water as well as with plankton cells (Avnimelech et al. 1982). In addition, the turbidity caused by clay particles interferes with light penetration into the water and further reduces primary production (Diana et al. 1991). Mitigation of mud turbidity is essential to allow normal phytoplankton growth in response to fertilizer inputs. A number of mechanisms may mitigate clay turbidity, including application of cations, input of organic matter, and use of green manure (Boyd 1990). In addition, turbidity problems may be prevented by pond design changes. All of these techniques are affected by local conditions.

Anticipated Benefits
The results generated in this study, in cooperation with similar studies in turbidity control at the other CRSP sites, will link bottom soil characteristics and water quality management for semi-intensive fish ponds. Turbidity problems prevail in many rain-fed ponds in Thailand, Cambodia, and Laos, where available fertilizer input is reduced in effectiveness by turbidity, resulting in poor fish yields and lack of interest in managing such ponds. The topic of turbidity control has been considered a priority by the Royal Thai Government Department of Fisheries, and also by the Asian Institute of Technology outreach project.

Identification of Beneficiaries
Culturists throughout Southeast Asia and other tropical countries who experience clay turbidity problems which limit light penetration and primary productivity in ponds.

Collaborative Arrangements
The Asian Institute of Technology will provide facilities for such research. 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

Sites: Asian Institute of Technology

Pond facilities: This experiment will be conducted in fish ponds in areas with turbidity problems.

Culture period: This experiment will be done over 150 days, including wet and dry season portions.

Stocking rates: Two sex-reversed male Nile tilapia per square meter.

Water management: Water depth in ponds will be maintained to 1 m by adding water weekly.

Nutrient inputs: All ponds will be fertilized with chicken manure at 500 kg/ha/wk supplemented with urea and TSP to provide 28 kg N/ha/wk and 7 kg P/ha/wk.

Other inputs: The inputs are actually design variables for this experiment. There will be five treatments included in the design, with each treatment having three replicates.
1. Control;
2. Cover 50 cm pond edges starting from the top of dikes with black plastic 3. (5-10 cm off pond dikes);
4. Cover pond bottoms with green manure (terrestrial weeds) to alter texture;
5. Cover pond bottoms with netting material (10-15 cm off bottoms) to prevent fish from accessing detrital materials;
6. Lime ponds biweekly using quick lime at a rate of 200 kg/ha.

Test Species: Nile tilapia

Sampling plan: Measurements of water quality will be taken biweekly including standard PD/A CRSP water quality parameters (Egna et al. 1987). Total solids, total suspended solids, total suspended organic solids and total dissolved solids will be measured biweekly. Secchi disk depth will be measured daily. Soil texture will be measured before and after the experiment. Particle size and settleability of suspended materials will be measured monthly. Fish growth will be measured based on initial and final mean weight. Diel analyses will be done monthly.

Statistical methods and hypotheses: The null hypotheses are that each treatment will not result in appreciable differences in Secchi disk depth, water quality, primary production, and fish growth compared to the control ponds. Significant differences will be tested using ANOVA and multiple regression.

Schedule/Time Line
This experiment will begin in 8/97 and complete in 2/98.

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

References
Avnimelech, Y., B.W. Troeger, and L.W. Reed, 1982. Mutual flocculation of algae and clay: evidence and implications. Science 216:63-65.

Boyd, C.E., 1990. Water quality in ponds for aquaculture. Agriculture Experiment Station, Auburn University, 482 p.

Diana, J.S., C.K. Lin, and P. J. Schneeberger, 1991. Relationships among nutrient inputs, water nutrient concentrations, primary production, and yield of Oreochromis niloticus in ponds. Aquaculture 92:323-341.

Egna, H.S., N. Brown, and M. Leslie, 1987. General reference: site descriptions, material and methods for the global experiment. PD/A CRSP Data Reports, Volume 1, Oregon State University, Corvallis, Oregon, 84 p.