SECTION A: NEW WORK PLANS

THAILAND RESEARCH

Note: Research under this work plan did not commence until July 2000. It was funded with funds made available when other Ninth Work Plan awards were declined. It appears here for the first time.

Objectives
1) To determine appropriate fertilization regimes in brackishwater ponds;
2) To investigate nutritional value and digestibility of specific marine phytoplankton as food organisms to tilapia; and
3) To exploit underutilized or abandoned shrimp ponds for tilapia production.

Significance
Many tilapia species are euryhaline and can grow in saline water after proper acclimation (Suresh and Lin, 1993). A variety of red tilapia have been successful cultured in saline waters (Watanabe, 1991). However, most of those tilapia culture trials were conducted in intensive systems with pelleted feeds, requiring frequent water exchanges or cages. Compared to the voluminous literature available for semi-intensive culture of tilapia in freshwater ponds, information on semi-intensive culture in saline ponds is almost non-existent. The species composition, feeding, and nutritional value of phytoplankton for tilapia growth in freshwater are relatively well understood, notably in works by Hepher (1982), Moriarty (1973), Bowen (1982), and recently the CRSP project (Egna and Boyd, 1997). The PD/A CRSP project did conduct a brief experiment on Nile tilapia grow-out in fertilized brackishwater ponds in the Philippines in 1984. In that experiment, the fish production was extremely low resulting from high mortality due to uncontrolled high salinity. We are assuming that fertilization rates for brackishwater ponds are similar to rates for freshwater ponds. Common CRSP guidelines have been 4:1 N:P inputs and 4 kg ha^-1 d^-1 of N.

During the last few years, the desire to culture tilapia in brackishwater ponds has been widely expressed in Southeast Asia as well as Central/South America (Green, 1997). The major reason for this need is that there are a large number of shrimp ponds available, either resulting from failure in shrimp farming or desires to diversify shrimp culture. Tilapia appears to be the most reasonable choice for such a culture system, because there are few domesticated finfish species that feed on low-cost natural foods, such as detritus and plankton. This interest in brackishwater culture is particularly strong in Thailand and Vietnam where shrimp culture is now commonly reduced to one crop per year, leaving the ponds empty for half a year. Tilapia culture is also attractive to shrimp farmers as a byproduct to utilize abundant phytoplankton in either shrimp ponds or their effluents.

Anticipated Benefits
This experiment will provide some guidelines on fertilization regimes for tilapia culture in brackishwater ponds, and on tilapia feeding and nutrition on natural organisms in these ponds. Successful trials of tilapia culture in brackish water ponds will provide farmers with a low-risk species available to stock in thousands of empty ponds in coastal Southeast Asia. Such aquaculture can be profitable in itself and over time may help reclaim these pond areas to agriculture.

Experimental Design
Location of Work:Asian Institute of Technology.

Methods:Pond research.

Pond Facility:18 cement ponds (6 m²) with soil bottoms.

Culture Period:5 months.

Stocking Density:2 fish m^-2.

Test Species:Thai strain red tilapia.

Nutrient Input:4 kg N ha^-1 d^-1 treatments of 4:1 and 2:1 N:P ratios.

Water Management:Water depth: 0.8 m; salinity: 10, 20, and 30 ppt.

Sampling Schedule:Regular CRSP protocols for water quality and biological parameters. Partial budgets will be calculated to estimate cost of inputs and value of fish crop. Biweekly assessment will be done for plankton composition and species eaten by fish.

Statistical Design and Analysis:2 x 3 factorial with 2 fertilizer inputs and 3 salinities; each treatment in triplicate. Results will be analyzed with ANOVA for significant difference.

Salinity will be initially regulated by trucking hypersaline water to AIT and diluting it to the appropriate concentration. Flooded ponds will be inoculated with phytoplankton. Marine parasite infections will be evaluated by visual examination of dead fish for ectoparasites.

An initial trial of marine plankton consumption will be done by producing monospecific cultures of Thalassiosira, Skeletonema, Chlorella, and Tetraselmis. Each species will be fed to young tilapia in the lab for two weeks. Growth will be determined to estimate prey consumption and nutrition from each algal species.

Null Hypothesis:Salinity and fertilizer treatments do not affect fish production.

Regional Integration
Fish productivity in brackishwater ponds will be compared with that of average production in fertilized freshwater ponds.

Regional Integration
The tilapia culture in brackishwater ponds is relevant to all countries in the Southeast Asia region where extensive coastal zones exist. The pond culture technologies developed for freshwater ponds by the CRSP project will be transferred to brackishwater systems where appropriate.

Schedule
July—September 2000

Report Submission
30 November 2000

References
Bowen, S.H., 1982. Feeding, digestion, and growth—quantitative consideration. In: R.S.V. Pullin and R.H. Lowe-McConnell (Editors), The Biology and Culture of Tilapias, ICLARM Conference Proceedings No. 7. International Center for Living Aquatic Resources Management, Manila, Philippines, pp. 141-156.

Green, B.W., 1997. Inclusion of tilapia as a diversification strategy for Penaeid shrimp culture. Symposium of Central American Aquaculture. Tegucigalpa, Honduras, pp. 85-93.

Hepher, B. and Y. Pruginin, 1982. Tilapia culture in ponds under controlled condition. In: R.S.V. Pullin and R.H. Lowe-McConnell (Editors), The Biology and Culture of Tilapias, ICLARM Conference Proceedings No. 7. International Center for Living Aquatic Resources Management, Manila, Philippines, pp. 185-203.

Egna, H.S. and C.E. Boyd, 1997. Dynamics of Pond Aquaculture. CRC Press, Boca Raton/New York, 437 pp.

Moriarty, C.M. and D.J.W. Moriarty, 1973. Quantitative estimation of the daily ingestion of phytoplankton by Tilapia nilotica and Haplochromis nigripinnis in Lake George, Uganda. Journal of Zoology, 171:15-24.

Suresh, R.V. and C.K. Lin, 1992. Tilapia culture in saline waters: a review. Aquaculture, 106:201-226.

Watanabe, W.O., 1991. Saltwater culture of tilapia in the Caribbean. World Aquaculture, 22:49-54.