Note: Experimental Design has been revised. See First Addendum to the Eighth Work Plan

Objectives
Significance
Anticipated Benefits
Identification of Beneficiaries
Experimental Design
Schedule/Time line
References

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 run off 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.

The Asian Institute of Technology and the Thai Department of Fisheries will collaborate with these analyses. The facilities for such research include ponds at AIT, as well as ponds constructed at the Udorn Thani Fisheries Station, Thai DOF and at other outreach sites. This collaboration is included in our Memorandum of Understanding for work in Thailand. 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: Southeast Asia; AIT and outreach facilities.

Pond facilities: These experiments will be conducted in fish ponds in areas with turbidity problems. The experiments will be conducted at an outreach site.

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

Stocking rates: Two Nile tilapia per square meter.

Water management: In ponds, water will be filled by rainfall and will remain stagnant.

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. Ponds 1.0 m deep. Application of organic fertilizer at optimum rates.

2. Ponds 1.0 m deep. Application of inorganic fertilizer at optimum inputs of P and N.

3. Cover pond dikes with rice straw and rice seedlings prior to flooding. Ponds 1.0 m deep, organically fertilized.

4. Ponds 1.0 m deep. Coverage of pond bottoms with green manure, composed of rice seedlings and terrestrial weeds to alter texture.

5. Ponds 0.75 m deep. Application of organic fertilizer at optimum rates.

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). Suspended materials will be measured in both particulate and soluble fractions. 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 on a monthly basis. 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 is planned for the first year of the new work plan. To fit into seasonal schedules, experiments will begin around September 1996 and complete in February 1997.

Final Report Submittal: Final reports will be completed with the 1996-97 annual report in Fall 1997.

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.

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. Pond Dynamics/Aquaculture Collaborative Research Data Reports, Volume 1. Oregon State University, Corvallis, Oregon. 84 pp.