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

1) To determine the effectiveness of common carp in removing organic matter from pond sediments and in recycling nutrients for tilapia ponds.

2) 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 the production of fish in the ponds. Testing and extension of soils management may also be done through the outreach program at AIT, which involves sites at other locations in southeast Asia.

Identification of Beneficiaries

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

The Asian Institute of Technology will collaborate with these analyses. The facilities for such research include ponds at AIT, as well as ponds at other outreach locations. 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 Udorn facilities.

Pond facilities: These experiments will be conducted in two systems: ponds with depth control at AIT, and ponds which are rain-fed at an outreach station. All treatments will be done at each station.

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

Stocking rates: this is a design variable. In experiment 1 (objective 1), common carp will be stocked at densities of 0, 1, 2, and 3 fish per 10 square meters, in combination with tilapia stocked at 2 per square meter. Each treatment will include 3 replicate ponds. For experiment 2 (objective 2), no specific stocking design is required.

Water management: In ponds at Udorn, water will be filled by rainfall and will remain stagnant. In ponds at AIT, water will be supplemented to maintain a set depth. For experiment 2, 3 treatments will be completed between grow-out cycles: repeated use without drying, seeding with terrestrial plants, and pond drying with soil treatment (liming and other additions) if necessary. Three ponds will be used for each treatment.

Other inputs: Ponds will be fertilized with organic fertilizers at 70 kg·ha^-1·wk^-1, and sufficient urea and phosphorus will be added to provide 0.5 g·m^-2·d^-1 N and 0.125 g· m^-2·d^-1 P.

Test Species: Nile tilapia, common carp.

Sampling plan: Measurements of water quality will be taken biweekly including standard PD/A 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 will be measured at flooding, halfway through the experiment, and prior to draining. All pond soil samples will be composite samples from the top 5 cm. After harvest, pond soil characteristics will be determined immediately, then weekly over the month long drying period. Soil characteristics of importance include P and N contents, total organic matter, moisture content, pH and DO. at the sediment/water interface.

In addition, benthic respiration will be estimated by enclosing a portion of the substrate in a dome and measuring decline in DO over time. These measures will also be done at the start, middle and end of the experiment.

Statistical methods and hypotheses: The null hypotheses are that each treatment will not result in appreciable differences in soil organic matter 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 second year of the new work plan. To fit into seasonal schedules, ponds experiments will begin around September 1997 and complete in February 1998.

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 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.

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

Lin, H. R. 1982. Polycultural system of freshwater 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.