THAILAND RESEARCH

Objectives
1. To establish the amount of N, P, suspended solids, dissolved solids and BOD discharged from pond waters during draining.
2. To evaluate several management practices to reduce loading of nutrients and solids in effluent waters.

Significance
Nutrient enrichment of pond waters is an essential practice management in aquaculture (Pillay 1990, Boyd 1990). However, the discharge of such nutrient-rich waters may result in deteriorating water quality in receiving waters, and is the subject of increasing regulation in many countries (Pillay 1992). Means to minimize the environmental impacts of effluents released from ponds would include minimizing the use of nutrients, managing drainage to retain most nutrients in the pond system, and maximizing the use of surplus materials in sediments by animals during grow out. Several of this topics are the subject of current CRSP proposals. Previous research in Thailand has indicated the most efficient nutrient application systems includes combined organic and inorganic materials at loading rates of 70 kg ha-1 d-1 chicken manure, and sufficient urea and phosphorus to provide 0.5 g m-2 d-1 N and 0.125 gm-2d-1 P (Knud-Hansen et al. 1993). These loadings provide organic matter to maintain high alkalinity levels, yet optimize loading of N and P so they are efficiently used in the pond. Such inputs also result in production of about 4800 kg/ha per 150-day grow out of tilapia (Diana et al. 1994).

Nutrient analysis of source and pond waters in Thailand indicate that such a fertilization system results in minimal increases in concentrations of P and N in pond waters through a grow out (Diana et al. 1994). While nutrient may be lost with any overflow water, these will not load receiving waters beyond normal levels during rain events. However, at draining the water quality of effluents may be considerably lower, due to accumulation of materials in pond sediments or in the water near the soil-water interface which is discharged at harvest (Pillay 1992). Several strategies could reduce such affects, including more gradual draining of the ponds, holding back of deep water at harvest, and removal of water into settling ponds or other fish ponds. The CRSP project has not monitored the quality of effluent waters, so there is no information available to evaluate the magnitude of this problem.

Anticipated Benefits
This experiment will fulfill several goals of the CRSP experiments. It will include further work on the soil-water interaction, at least during harvest. It will also evaluate the environmental impacts of fish culture, particularly related to effluent discharge. Once these results are available, methods to implement the best management schemes, such as means to discharge the final polluting portion of the water or better methods to harvest fish without draining, can be determined. Such experiments should be guided by effluent studies done above and by other experiments previously conducted in treatment systems.

The environmental impacts of aquaculture could include many characteristics, but certainly major concerns include release of exotic or diseased animals, as well as loading of receiving waters by aquaculture effluents. Research to better understand the effluent conditions will help managers involved in aquaculture regulation. Such work also provides a direct link between the freshwater aquaculture program of the CRSP and brackish water work in Honduras.

Identification of Beneficiaries
Culturists throughout south east Asia and other tropical countries who experience effluent problems which affect their ability to discharge nutrients into receiving waters.

Collaborative Arrangements
The Asian Institute of Technology will collaborate with these analyses. The facilities for such research ponds are 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 in sequence. (1) Ponds with tilapia receiving chemical fertilizers and commercial feeds, and (2) ponds with chemical fertilizers only which had different draining and harvesting procedure. In both experiments, five different pond draining and fish harvesting strategies will be tested to minimize effluents loading to receiving waters.

Experiment 1
Ponds / sites: 15 earthen ponds 200 m2, at AIT.

Culture period: 120 days.

Test Species: Sex-reversed Nile tilapia about 100 g size @ 1.5/m2.

Nutrient inputs: Urea-N 28 kg/ha/week ; TSP-P 7 kg/ha/week (N:P ratio 4:1). Commercial feed (30% CP). Feeding rates will be readjusted on a weekly basis for each pond as the amount of feed consumed during a 1-h period each in the morning (1000-1100 h) and the afternoon (1400-1500 h) on the first day of each week. after this evaluation of satiation feeding, 50% satiation feeding will be provided for the next 6 days.

Water management: The water depth of each pond will be maintained at 1 m by replacing losses to seepage and evaporation.

Treatment Design: Five treatments in triplicate randomized block design.

1. No pond draining; fish harvested by seining application of tea seed cake.
2. Complete draining after lime flocculation of suspended solids; fish harvested from harvesting pit.
3. Complete draining; fish harvested from harvesting pit.
4. Normal draining and harvesting (draw down water level to 50 cm, two seinings, then complete draining and fish collection).
5. Normal draining and harvesting, effluent diverted to ponds of treatment.

Sampling plan:

Nutrient: Samples of feed added to ponds will be collected monthly and analyzed for total N and total P. Samples of input water will also be analyzed for N, P and organic C. Five fish per pond will be sampled at stocking and harvest for total N and total P.

Water: Standard CRSP protocol (Egna et al. 1987).

Sediment: Analysis of top 10 cm core samples for total N, total P and organic C before stocking and after harvest. Sediment deposition will be measured in two treatments where seining will not be done for fish harvest.

Effluent: Effluents from ponds during draining will be analyzed. Effluent samples will be collected from the outlet pipe of the pump during draining at different depth levels (1.0-0.5, 0.5-0.25 and 0.25-0.0 m). Effluents will be analyzed for total N, total P, organic C, total solids, suspended solids, dissolved solids, settleable matter and BOD5.

Experiment 2
This experiment will be conducted in same ponds used for experiment 1 having the same 5 draining and harvest treatments. Only empty ponds will be filled with water. Fish will be cultured semi-intensively.

Test Species: Nile tilapia, 2/m2.

Culture period: 90 days.

Other input: Weekly application of urea and phosphorus at 0.4 g m-2 d-1 N and 0.1 g m-2 d-1 P.

Sampling plan: Water quality measurements according to standard CRSP protocol (Egna et al. 1987). Monthly fish sampling (10% of stocked fish) for growth.

Statistical methods and hypotheses: The null hypotheses are that different draining and harvesting practices will not result in significant differences in effluent loading of receiving waters, pond water quality, or fish growth. Significant differences will be tested using ANOVA and multiple regression.

Schedule/Time line
These two experiments will be conducted during 2-11/97.

Final Report Submittal: Preliminary report of experiment 1 will be submitted in Fall 1997 and 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.

Diana, J.S., C.K. Lin, and K. Jaiyen. 1994. Supplemental feeding of tilapia in fertilized ponds. Journal of the World Aquaculture Society 25:497-506.

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.

Knud-Hansen, C.F., C.D. McNabb, and T.R. Batterson. 1993. The role of chicken manure in the production of Nile tilapia (Oreochromis niloticus). Aquaculture and Fisheries Management 24:483-493.

Pillay, T.V.R. 1990. Aquaculture: principles and practices. Fishing Book News, London.

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