Note: Experimental Design has been revised. See Addendum to the Ninth Work Plan
Note: Schedule has been revised. See Addendum to the Ninth Work Plan

Objectives

1) To assess the pond mud nutrient recovery by taro plants.
2) To assess pond mud characteristics after taro-fish culture.
3) To compare fish growth between with and without taro integration.

Significance
Regular fertilization in fish ponds accumulates nutrients in pond mud. One hectare of old pond mud was reported to have the equivalent of 1.85 tons of urea and 2.30 tons of TSP (Shrestha and Lin, 1996a) or 2.8 tons of urea and 3.0 tons of TSP (Yang and Hu, 1989). Pond muds are major sink for phosphorus and adsorption capacity is related to mineral composition and clay content of pond muds (Shrestha and Lin, 1996b). Release of adsorbed P to water column is minimal and phytoplankton are not as effective to utilize adsorbed P as rooted crops. Roots extended in interstitial water of soil provide better opportunity to extract P from soil (Denny, 1972; Boyd 1982; Smart and Barko, 1985) and hence, pond muds have been widely used to fertilize land crops (Muller, 1978; Little and Muir, 1987; Christensen, 1989; Shrestha and Lin, 1996a). However, removing pond mud is labor intensive and its practicability is questionable (Edwards et al., 1986). Alternatively, taro-fish culture may be considered to utilize reserve nutrient in muds. Taro (Colocasia esculenta) is a semiaquatic submerged plant which is seen to grow as tall as one meter. It can utilize adsorbed nutrients from pond sediments efficiently (Shrestha and Lin, 1996a). Water levels of ponds can be increased as taro grows and fish can be stocked. However, taro cultivation in ponds may lead to space competition for fish. Additionally, taro shoots will provide substrate for the growth of epiphytic algae which is consumed by tilapia (Bowen, 1982; Lowe-McConnell, 1982; Shrestha and Knud-Hansen, 1994).

Anticipated Benefits
Results of the experiment will provide information on the possibility of taro-fish culture and recycling of pond mud nutrients which are otherwise wasted. It will generate information on bottom mud characteristics altered by rooted plants. It may benefit small-scale farmers of Asian countries for resource utilization where taro is commonly grown as a root crop.

Research Design
Location: Agriculture University, Nepal (or AIT, if not possible)

Methods: Pond Research

Pond Facility: 9 ponds of 200 m² size

Culture Period: 6-7 months

Test Species: Nile tilapia (Oreochromis niloticus); taro (Colocasia esculenta)

Stocking Density: Tilapia 2/m²; taro plant spacing 0.7 x 0.4 m

Nutrient Input: Weekly fertilization by urea and TSP @ 4 kg N and 1 kg P·ha^-1·d^-1

Water Management: After taro planting, water level will be increased as the height of taro plant increases. Once the water level reaches 30 cm, fish will be stocked. Water level will be increased with growth of taro up to 1 m depth.

Sampling Plan: Biweekly and monthly diel water quality following standard CRSP protocol. Initial and final pond mud sampling for organic C, total N, available N, total P, available P, soil pH. Partial budgets will be estimated for cost of inputs and value of fish and taro. Fish growth and survival will only be assessed at the end of the experiment due to sampling difficulties. Fish and taro will be harvested by draining. Nutrient budgets will be estimated for all ponds. We intend to expand our studies into Nepal, and would prefer to conduct this experiment there if possible. If such arrangements cannot be made, we will conduct the study at AIT.

Experimental Design, Hypotheses and Statistical Methods: Experiment will have 3 treatments in triplicates:
(a) taro-fish culture, (b) only fish, and (c) only taro. The null hypothesis is that there will be no difference in mud nutrient differences, soil characteristics, fish growth, and nutrient recovery between two treatments. Significant differences will be tested using ANOVA.

Regional Integration
Taro is a popular crop in southeast Asia and other parts of Asia. Nile tilapia is commonly cultured in the region. Small-scale farmers are resource limited and taro-fish culture may utilize waste nutrient resources otherwise.

Schedule
June - December 1999

Report Submission
March 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.

Boyd, C.E., 1982. Water quality management for pond fish culture. Developments in Aquaculture and Fisheries Science, 9. Elsevier, Amsterdam, 318 pp.

Christensen, M.S., 1989. Evidence for differences in the quality of fish pond muds. Aquabyte, 2:4-5.

Denny, P., 1972. Sites of nutrient absorption in aquatic macrophytes. Journal of Ecology, 60:819-829.

Edwards, P., K. Kaewpaitoon, E.W. McCoy, and C. Chantachaeng, 1986. Pilot small-scale crop/livestock/fish integrated farm. AIT Research Report, 184, Bangkok, Thailand.

Lowe-McConnell, R.H., 1982. Tilapias in fish communities. 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. 83-113.

Little, D. and J. Muir, 1987. A Guide to Warm Water Aquaculture. Institute of Aquaculture, University of Stirling, Stirling, Scotland, 238 pp.

Muller, R, 1978. The aquacultural rotation. Aquaculture Hungarica, 1:73-79.

Shrestha, M.K. and C.F. Knud-Hansen, 1994. Increasing attached microorganism biomass as a management strategy for Nile tilapia (Oreochromis niloticus) production. Aquacultural Engineering, 13:101-108.

Shrestha, M.K. and C.K. Lin, 1996a. Recycling of mud nutrients as fertilizer to rooted crops. World Aquaculture Society, Abstracts from World Aquaculture ‘96, pp. 370-371.Shrestha, M.K. and C.K. Lin, 1996b. Determination of phosphorus saturation level in relation to clay content in formulated pond muds. Aquacultural Engineering, 15:441-459.

Smart, R.M. and J.W. Barko, 1985. Laboratory culture of submerged fresh water macrophytes on natural sediment. Aquatic Botany, 21:251-263.

Yang, H. and B. Hu, 1989. Introduction of Chinese integrated fish farming and major models. In: Integrated Fish farming in China. NACA Technical Manual 7. A World Food Day Publication of the NACA, Bangkok, Thailand.

Note: Schedule has been revised. See Addendum to the Ninth Work Plan

Objectives

1) To assess the efficiency of snakehead in controlling overpopulation of mixed-sex Nile tilapia in ponds.
2) To assess growth and production of Nile tilapia in monoculture and polyculture with snakehead.

Significance
Aquaculture for lower trophic level species such as tilapia presents the greatest potential for efficiency (Welcomme, 1996). However, overpopulation of tilapia in the culture system causes stunting due to shortage of food, which is a problem in tilapia culture. Various methods of population control, such as culture in cages, culture with predators, intermittent harvesting, hybridization, induction of sterility, and production of super male fish (YY-male) have been described (Mair and Little, 1991). However, population control of tilapia through culture with predators is not as well studied. Snakehead (Channa striata) has been reported to be used in polyculture with tilapia to keep the population of tilapia under control, or with carps to keep out other extraneous pest fish in the pond system (Wee, 1982). Snakehead swallow their prey whole (Diana et al., 1985), are highly predaceous, and prey on live tilapia fry when provided (Kaewpaitoon, 1992). A population including 5% snakehead with tilapia has been demonstrated to control tilapia recruitment (Balasuriya, 1988). It is unclear how widely such a ratio can be used, since fry production and predator consumption are strongly site-specific. In Thailand, negligible tilapia recruitment is generally found where snakehead was collected from tilapia ponds during harvest, supporting the general concept.

Anticipated Benefits
The results of this study will evaluate an alternative technique for tilapia culture system. Nile tilapia production will expand and increase where sex-reversed tilapia are not available. It will benefit culturists throughout southeast Asia and other tropical countries where tilapia are commonly cultured and there is no tilapia production of sex-reversed fry.

Research Design
Location: AIT, Thailand (or Nepal, if possible)

Methods: Pond research

Pond Facility: 18 earthen ponds, 200 m² size

Culture Period: 150 days

Stocking Density: 2 tilapia/m²; snakehead as specified in treatment design

Test Species: Nile tilapia (Oreochromis niloticus); snakehead (Channa striata)

Nutrient Input: Weekly chemical fertilization by urea and TSP @ 4 kg N and 1 kg P·ha-1·d-1

Water Management: Maintain at 1 m depth

Sampling Plan: Biweekly and monthly diel water quality following standard CRSP protocol, monthly growth and total harvest of fish. Partial budgets will be calculated to estimate input costs and fish value.

Statistical Design, Null Hypothesis and Statistical Analysis: Experiment design will consist of 6 treatments in triplicate:

a) monoculture of sex-reversed tilapia,
b) monoculture of mixed-sex tilapia,
c) polyculture of mixed-sex tilapia and snakehead at 10:1 ratio,
d) polyculture of mixed-sex tilapia and snakehead at 20:1 ratio,
e) polyculture of mixed-sex tilapia and snakehead at 40:1 ratio, and
f) polyculture of mixed-sex tilapia and snakehead at 80:1 ratio.
Stocking size will be about 15 g for tilapia, and a consistent size of snakehead, generally < 5 g.


The null hypotheses are that different ratios of tilapia:snakehead will not have differing effects on tilapia recruitment, and that polyculture or monoculture will have similar tilapia growth and production. Significant differences will be tested using ANOVA.

Regional Integration
Nile tilapia are commonly cultured in Southeast Asia and are introduced in most of the tropical and subtropical Asia. Snakehead are a common indigenous species of tropical and subtropical Asia and are cultured in Thailand.

Schedule
July to November 1999

Report Submission
January 2000

References
Balasuriya, C., 1988. Snakehead (Channa striata) as a controlling predator in the culture of Nile tilapia (Oreochromis niloticus). M.S. thesis, Asian Institute of Technology, Bangkok.

Diana, J.S., W.Y.B. Chang, D.R. Ottey, and W. Chuapoehuk, 1985. Production systems for commonly cultured freshwater fishes of southeast Asia. International Program Report, No. 7. Great Lake and Marine Water Center, University of Michigan, Ann Arbor, Michigan.

Kaewpatoon, K., 1992. Utilization of septage-raised tilapia (Oreochromis niloticus) as a feed for snakehead (Channa striata). Ph.D. dissertation, Asian Institute of Technology, Bangkok.

Mair, G.C. and D.C. Little, 1991. Population control in farmed tilapias. NAGA, The ICLARM Quarterly, 4(2):8-13.

Wee, K.L., 1982. The biology and culture of snakeheads. In: J. Muir and R.J. Roberts (Editors), Recent Advances in Aquaculture. Croom Helm Press, London, pp. 179-213.

Welcomme, R.L., 1996. Aquaculture and world aquatic resources. In: D.J. Baird, M.C.M. Beveridge,
L.A. Kelly, and J.F. Muir (Editors), Aquaculture and Water Resource Management. Blackwell Science, Ltd, London, pp. 1-18.

Note: Schedule has been revised. See Addendum to the Ninth Work Plan

Objectives

1) To use effluents from intensive catfish ponds as nutrients for tilapia culture ponds, and thus to reduce effluent effects from catfish culture.
2) To gain extra fish production at low cost, making aquaculture more profitable to farmers.

Significance
Clarid catfish has been one of the most popularly cultured freshwater fish in Southeast Asia. The present annual production in Thailand is estimated to be 50,000 tonnes. As an air breather, catfish can be grown at extremely high density (100 fish/m²) with standing crop in pond culture reaching as high as 100 tonnes/ha (Areerat, 1987). The fish are mainly cultured intensively and fed with trashfish, chicken offal or pelleted feed, which generally causes poor water quality and heavy phytoplankton blooms throughout most of the grow-out period. To maintain the tolerable water quality for fish growth, pond water is exchanged at later stages of the culture cycle (which is 120 to 150 days). The effluents containing concentrated phytoplankton biomass and nutrient, are unsuitable to irrigate rice fields because unbalanced N:P ratios (high nitrogen content) cause rice to fail to fruit. Wastewater disposal from catfish ponds has become a serious problem, especially in the Northeast Thailand where surface waters are in short supply. Farmers often discharge the wastewater to adjacent rice fields, which are damaged by this input. Apparently benefiting from the nutrient rich effluents, aquatic spinach (Ipomea aquatica) often grows profusely in those areas. This aquatic macrophyte can be harvested as a vegetable which is widely consumed throughout the region. To fully utilize the effluents, unproductive wetlands can be excavated for tilapia culture and water spinach planted to cover a portion of the pond surface area. Such diversification and integration are regarded as important practices to enhance aquaculture sustainability (Adler et al., 1996; Pillay, 1996).

The wastes from catfish cultured in cages have been shown to be effective for producing phytoplankton to support Nile tilapia culture in the same pond (Lin et al., 1990; Lin and Diana, 1995). Similarly, tilapia reared in cages, feeding on phytoplankton in intensive channel catfish ponds, were shown to improve pond water quality as well as produce an extra crop (Perschbacher, 1995). Although use of plants, such as water hyacinth, to remove nutrient from sewage effluents is done in many areas, few examples have been established for intensive aquaculture in the tropics. Preliminary experiments done at AIT show that water spinach grew rapidly in effluents of domestic wastewater, but the nutrient uptake capacity of this plant yet has to be determined.

Anticipated Benefits
The integrated recycle system will be able to produce tilapia and water spinach using effluents from intensive catfish ponds, which otherwise would be a source of pollution to surface waters. Economically, the profit margin of catfish culture will be augmented with tilapia and water spinach crops at minimal cost. This system will provide scientific information on mass balances of nutrients and optimization of biological productivity.

Research Design
Location: AIT campus, Bangkok

Pond Facility: 15 earthen ponds of 200 m² size

Culture Period: 150 days

Stocking Density: 25 catfish/m2; 2 tilapia/m²

Test Species: Hybrid catfish (Clarias macrocephalus x C. gariepinus); Nile tilapia (Oreochromis niloticus)

Nutrient Inputs: Pelleted feed for catfish, effluents recirculated to tilapia ponds; tilapia pond will also be fertilized for the first month.

Water Management: Pond water depth to be kept at 1 m; in recirculation treatment the water in catfish ponds will be continuously circulated to tilapia ponds at a rate of one exchange per week. No water circulation will be done in the first month.

Sampling Schedule: Water quality parameters will be analyzed biweekly and diel samples monthly, following standard CRSP protocols. Partial budgets will be estimated to assess costs and value of fish.

Statistical Design and Analysis: The experiment treatments will include catfish alone (control), catfish and tilapia, or catfish plus tilapia and spinach; each treatment will be conducted in triplicate. Ponds will be flooded and stocked with fish. Spinach treatments will have 1/4 of the pond area with bamboo stakes at 3 x 3 m intervals. Spinach will be attached to these stakes. Once spinach reaches full cover, it will be harvested biweekly to reduce crowding. Nutrient budgets will be determined.

Null Hypothesis: Water circulation to tilapia/spinach ponds does not affect water quality and fish production.

Impact Indicators
The experimental results on fish production, economical return and water uses will be compared to average catfish and tilapia production of a select group of Thai farmers in the Bangkok area.

Regional Integration
In the SE Asian region, both clarid catfish and tilapia are widely cultivated with traditional segregated pond culture systems. The integrated systems will be a new step in production technology that will promote efficient production as well as environmental sustainability.

Schedule
15 March to 1 August 1999

Report Submission
15 November 1999

References
Areerat, S., 1987. Clarias culture in Thailand. Aquaculture, 63:355-362.

Adler, P.R., F. Takeda, D.M. Glenn, and S.T. Summerfelt, 1996. Enhancing aquaculture sustainability through utilizing byproducts. World Aquaculture, 27:24-26.

Lin, C.K. and J.S. Diana, 1995. Co-culture of catfish (Clarias macrocephalus x C. gariepinus) and tilapia (Oreochromis niloticus) in ponds. Aquatic Living Resources, 8:449-454.

Lin, C.K., K. Jaiyen, and V. Muthuwan, 1990. Integration of intensive and semi-intensive aquaculture: Concept and example. Thai Fisheries Gazette, 43:425-430.

Perschbacher, P.W., 1995. Algal management in intensive channel catfish production trials. World Aquaculture, 26:65-68.

Pillay, T.V.R., 1996. The challenges of sustainable aquaculture. World Aquaculture, 27:7-9.