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II. Summary of Activities and Accomplishments

II. Summary of Activities & Accomplishments

1 September 1994 to 31 August 1995

Major accomplishments during the current reporting period include the completion of a number of the activities scheduled under the Sixth and Seventh Work Plans. Among these were further refinements to several CRSP aquaculture pond models, improvements to the POND© decision support system, increased on-farm research trials, and continued environmental monitoring. Activities described in the Interim Work Plan were begun during this reporting period. As in the previous reporting periods, research was conducted both at the established CRSP research facilities and in farmers' ponds in the field. Research activities of the Sixth, Seventh, and Interim Work Plans continue. As always, efforts to disseminate research results continued through a variety of avenues.

Global Studies & Activities

The strength of the CRSP network is evidenced by the portability of research activities between sites. Several studies that were originally scheduled for Rwanda have been modified and conducted at other sites, an indicator of the global nature of CRSP research. These research projects are now being carried out in Honduras, the Philippines, and the U.S.

In Thailand and Honduras, researchers began the Global Experiment. The objectives are to develop nutrient budgets for nitrogen and phosphorus for semi-intensively managed freshwater and brackish water production ponds, and to quantify the effect of pond management strategies on water and sediment quality. This study will help researchers quantify the potential pollution impact of ponds using semi-intensive management strategies.

In an effort to characterize African soils to support new site selection, research was conducted to determine the most reliable estimators of lime requirements for specific soil types. Research was carried out both in the laboratory and in isolation columns in ponds at OSU. Results indicate that no lime requirement estimator can be used for every soil type. At Auburn, researchers studied the phosphorus adsorption capacity and availability of added phosphorus in soils collected in Thailand. Results indicate that the relative abilities of pond bottom soils to adsorb and release phosphorus added to ponds in fertilizers or feeds can be assessed from the phosphorus adsorption capacity of the soil. This appears to be a more useful technique than traditional phosphorus extraction methods as an index of phosphorus status in aquaculture ponds. Since the phosphorus adsorption capacity was highly correlated with the clay content of soils, a knowledge of clay content will permit a rough assessment of phosphorus status.

Researchers on the Global Social Sciences Project investigated how and to what extent CRSP research is reaching the institutions that serve farmers, and whether these institutions influence the practices of fish farmers. This study will facilitate the conduct of research that meets farm-level needs in an environmentally and socially sustainable way. The institutional context and connections of the CRSP are portrayed based on information obtained from U.S. scientists, host country counterparts, and others knowledgeable about the program. Researchers interviewed over 125 farmers in Rwanda, Honduras, Thailand, and the Philippines and collected data from cooperating institutions in each Host Country. An economic analysis examined the financial viability of different feeding and pond fertilization approaches associated with several years of parallel experimentation.

Results indicate that tilapia growers in each of the countries face vastly different institutional systems supporting tilapia production. Therefore, the researchers believe that CRSP efforts should emphasize infrastructure development and improved functioning of the private sector when the CRSP has the opportunity to do so. Currently, poorly organized markets and distribution systems hinder aquaculture development. As markets for tilapia expand, so will demand for production and support services. The development of private sector marketing services are crucial for sustained aquacultural development. Efforts to enhance the transfer and utilization of CRSP research results will require greater attention to actual and potential pathways of influence and information flow to the farm and village. Although the provision of information directly to end-users is not a mandate of the CRSP, a better understanding of the actual and potential pathways of influence and information flow will help researchers focus their efforts to include appropriate influential institutions as research partners.

The Central Data Base, the world's largest standardized aquacultural data base, is used for global analyses and model building. The Data Base is the central repository for data from the CRSP global experiments. Data from other CRSP experiments, particularly those experiments conducted in the Philippines and Thailand, are also included. The Central Data Base has been housed at the University of Hawaii at Hilo since mid-1993. During this reporting period, all incoming data were processed, all data requests were filled, a new data entry manual was drafted, database structure was modified to handle textual data, and the possibilities of creating a World Wide Web site were explored in cooperation with the PMO.

Central America

The Honduras site continues to facilitate linkages among private sector aquaculturists, the Government of Honduras, universities and schools in Honduras and the U.S., and USAID. Researchers continued monitoring estuarine water quality in the riverine and embayment estuaries of the Gulf of Fonseca. They participated in discussions with other project leaders in the area to share ideas about approaches to solving problems of water quality. David Teichert-Coddington, the CRSP researcher in Honduras, was instrumental in organizing the Third Central American Shrimp Symposium, which attracted participants from throughout the region.

Researchers at the Choluteca station characterized shrimp farm effluents as the first step in estimating the carrying capacities of local estuarine systems for shrimp. Intake and discharge from shrimp farms located on the estuaries of the Gulf of Fonseca were sampled during both the rainy and dry seasons during 1993-94. Results showed a mean net consumption of inorganic nitrogen and phosphorus, and a mean net discharge of organic matter. Most of the nitrogen entered and left the ponds through water exchange; most phosphorus entered the ponds as feed but left by water exchange. Pond discharge of both nitrogen and phosphorus increased linearly with the feed conversion ratio. The conversion of feed and nitrogen to shrimp flesh was greater during the wet season than the dry season.

Earlier studies had demonstrated that shrimp production was similar at protein levels between 20% and 40%, when shrimp were stocked at densities between 5 and 11/m2, and that feed efficiency was relatively low. In a related trial, shrimp stocked at 7.5/m2 during the dry season were not significantly affected by a 50% reduction in feeding rate. Although wet season production in this trial was significantly impacted by the 50% reduction in feeding, feed efficiency was improved. These results suggest that too much feed was applied during both the dry and wet seasons, although more overfeeding occurred during the dry season. It is possible that a comparatively high protein diet might improve shrimp growth and feed conversion. If a high protein feed is used at a comparatively low feeding rate (low compared with that employed with lower protein diets), it is possible that nitrogen levels in pond effluents will be reduced. Researchers are testing the effect of diet protein level on food conversion and nitrogen effluents during both the wet and dry seasons. If the results indicate that nitrogen discharge responds to both feeding rate and diet protein level, farmers will have economic and ecological incentives to feed at appropriate rates with an appropriate protein level.

Taura Syndrome is the cause of high mortality in some Central American shrimp ponds. In response to an urgent need for information on how to manage ponds affected by Taura Syndrome, researchers at the Choluteca station investigated the relationships among stocking density, survival, and shrimp yield in affected ponds. Penaeus vannamei were stocked in ponds on two farms during the wet season and on three farms during the dry season. At each farm, four different stocking rates were used. Researchers found no significant correlation between stocking density and survival during either the wet or dry season, nor did they find a seasonal influence on survival. Shrimp production rose with increased density, regardless of the season. Farming income is related to both biomass and shrimp size. Thus, farmers' net income increased with density during the wet season, but decreased or remained neutral with an increase in density in the dry season. During the wet season, production increased without a decrease in size of harvested shrimp; however, during the dry season, mean shrimp size decreased.

Although the main CRSP research site in Honduras is now in Choluteca, the freshwater site at El Carao continues to be operated as a CRSP sub-station. Researchers there studied the effects of nitrogen fertilization on water quality and tilapia yield in ponds supplied with adequate phosphorus. They found that fish yields were not significantly correlated with nitrogen input, despite higher phytoplankton biomass. Cool water temperatures apparently inhibited fish growth, rendering the fish unable to take advantage of higher available nutrient supply.

It is an indicator of the resiliency of the collaborative research process that research experiments are portable among sites. As an example, researchers noted that worldwide, red tilapia have generally been perceived by producers as having greater consumer acceptance, although existing research indicates that the growth rate of Nile tilapia is superior. In trials currently underway, Auburn researchers working at the El Carao Fish Culture Station in Comayagua, Honduras, are investigating reproductive efficiency of Nile tilapia and red tilapia, their comparative growth and the efficacy of sex reversal. The work is being carried out at the El Carao Station, but the impact of the results will be important for tilapia farmers throughout the world. Researchers at El Carao are also investigating the growth and efficiency of sex reversal of Nile tilapia that are fed hormone-treated feed stored under different storage regimes, another study that was originally programmed for the Rwanda site.

East Africa


The continuing unrest in Rwanda forced the CRSP to close its research site there. The losses, in terms of lost and disrupted lives, and lost expertise of both the professional staff and the area farmers, are immeasurable. In an effort to minimize the overall loss to the region and to the aquaculture community, the CRSP has been actively engaged in selecting a new site from which to build regional capacity in aquaculture research. The selection process has entailed much research, several site visits, extensive correspondence, laboratory analyses of soils and water samples, and other exploratory efforts. The process is still underway. Site selection criteria have been developed, data have been collected from several sites, promising sites have been evaluated, and work has begun on a characterization of African soils. Promising sites were identified as: Sagana Fish Culture Station in Kenya, Bunda College Station and Domasi Experimental Fish Farm in Malawi, and several sites in Zimbabwe, Zambia, and Tanzania. A final determination will be made by the time the Continuation Plan is effected.

In addition to soil studies, members of the Africa team at Auburn are investigating the effect of temperature on appetite and growth response of tilapia fry. The results of the study will enable researchers to investigate the effects of growth rate on the timing of gonadal differentiation and the efficacy of sex reversal, leading to more efficient use of hormone-treated feed. Preliminary studies have not yielded sufficient data, and further trials are planned to obtain the needed data points.

Work at OSU examined the efficacy of a short-term immersion procedure for masculinizing tilapia. Two synthetic androgens--17a-methyldihydrotestosterone (mestanolone) and 17a-methyltestosterone--were evaluated at two concentrations, using 3-hour exposures at 10 and 13 days after fertilization. Results indicate that short-term immersion in 17a-methyldihydrotestosterone at a concentration of 500 µg/l shortens the treatment period, thereby reducing possible worker exposure to anabolic steroids.

Southeast Asia

Thailand project personnel directed considerable resources into outreach efforts during this reporting period. Two workshops were held for ten fisheries officers from four provinces in Northeast Thailand, including Udorn, Nong Khai, Sakon Nakhon, and Loei. Each of the fisheries officers attending selected four to six small-scale farmers from his or her province to participate in the high-input green water scheme recommended by the CRSP program based at the Asian Institute of Technology (AIT). Biologists from the Udorn station monitored the farmers' activities. Most farmers started their growout cycle at the beginning of the rainy season in May and June 1995. The researchers are faced with complications in attaining the production data because most farmers harvest fish in small numbers upon demand by local consumers or keep fish for their own consumption. Despite the difficulties in data collection, the farmers provided positive feedback about the trials.

Researchers at AIT undertook a study to evaluate caging densities and pond loading rates for tilapia that were caged and fed within semi-intensive ponds with small tilapia at large. Such a system could be an effective means to produce large tilapia efficiently. Caged tilapia were stocked at five densities, and held in ponds loaded at two rates for 90 days of culture. Growth rates of the caged tilapia were similar regardless of stocking density; however, survival rates differed significantly with cage density, with fish at higher densities exhibiting very high mortality rates. Growth and mortality rates of the uncaged tilapia were similar to rates found using other culture systems, even though the only source of nutrients was the unused feed, fecal matter, and excretory products of the caged fish. Water quality did not deteriorate within the ponds at either loading rate. Cage stocking densities of 64 fish per m3 resulted in good survival and significant growth.

The effects of fertilization on growth and production of tilapia in rain-fed ponds in Thailand were studied during this reporting period. Researchers evaluated fertilization strategies for these ponds based on strategies developed for ponds that receive regular water inputs. Regular pond fertilization resulted in the highest fish growth rates. Irregular fertilization yielded lower growth, and fertilizing only at time of stocking yielded the lowest growth. Results of this study will impact farmers in northeast Thailand, whose ponds are typically rain-fed, and who have lacked research-based information on appropriate fertilization regimes.

A different study is currently underway to assess the effect of another fish species on the water quality and yield of tilapia, and of all fish, in deep, rain-fed ponds. Treatments differed in stocking density of common carp into earthen ponds stocked with tilapia and fertilized with chicken manure, urea, and phosphorus. After five months, the ponds will be harvested. Standard protocol will be used for physical and chemical monitoring of ponds for most sampling procedures.

Increasing the carrying capacity of the pond or size at harvest of tilapia requires more intensive management, which largely involves supplemental feeding. Researchers attempted to determine the upper limits to tilapia production using supplemental feeds. Fish were stocked at four densities and fed to satiation during the 146-day culture period. The highest growth rate and survival occurred in lower-density ponds. Researchers could not explain why the higher densities did not have correspondingly high growth and survival rates. The best recommendation currently is to stock fish at 3/m 2 under intensive feeding regimes.

Deep (approximately 2.5 m) rain-fed ponds become more highly stratified than do shallow ponds and are therefore less likely to be stirred by convective overturn at night or by wind-induced mixing. Thus, oxygen depletion in the hypolimnion is more likely. A study was conducted at AIT to describe and quantify the diel temperature cycles and dissolved oxygen (DO) stratification in these deep ponds. During sunny days in the dry season, the deep pond had a slightly deeper mixed layer than is characteristic of ponds at more sheltered sites. The bottom water below 2 m depth was almost completely isolated from the upper water, receiving only minimal transport of oxygen from above. During the rainy season, the isolation below 2 m was maintained even through a dark rainy day. These results show that active mixing may be necessary to maintain deep ponds as suitable culture environments for some species.

Following up a study of the relationship of pond depth to fish production, the Thailand group investigated the effects of pond surface area on fish production. Researchers examined earthen ponds that are similar in area to those used by farmers in Thailand and the Philippines, and the results of this experiment should have general applicability in the region.

Researchers at University of Hawaii investigated carbon dioxide (CO2) exchange between pond water and the atmosphere. Although oxygen exchange is routinely estimated in free water studies, far less attention has been given to diffusion of carbon dioxide, which may be significant. Researchers analyzed data from their pond research facility in the U.S. to quantify the rates of exchange of carbon dioxide between pond water and the atmosphere in fertile earthen ponds, and to identify factors which determine these rates of exchange. An analysis of these data showed that total carbon dioxide concentrations varied little during the day, but showed a perceptible dip during mid-day, reflecting photosynthetic uptake. Wind speeds directly above the water surface were measured, and researchers observed that the windiest periods occurred mainly during daylight hours. Analysis showed that the concentration of free carbon dioxide and wind speed together accounted for 81% of the variation in the diffusion rates during the diel cycle. Thus, prediction of diffusion rates requires only observed carbon dioxide concentrations and wind speed, although photosynthetic demand can be the primary determinant of concentrations under some conditions.

Researchers investigated whether adding carp to a tilapia monoculture would increase the productivity of the pond system. Because tilapia are primarily planktivores, researchers hypothesized that the addition of carp would increase productivity by converting currently unutilized benthic matter into fish flesh. Researchers stocked ponds with tilapia and added carp at varying stocking rates. Ponds were fertilized weekly with chicken manure, urea and TSP. Preliminary results indicate slow, uniform growth for tilapia, possibly because larger tilapia than called for in the experimental protocol were stocked erroneously. Carp growth proved to be extremely sensitive to and inversely related to stocking density. Although turbidity was higher in ponds stocked with carp, there was little indication of any other difference in water quality between the monoculture and the polyculture ponds.

In the Philippines, three strains of Oreochromis niloticus were grown at Central Luzon State University's Freshwater Aquaculture Center (FAC) to compare their growth performance. The three strains were: a FAC strain that had descended from tilapia imported to the Philippines in the 1970s; a Thai strain descended from tilapia imported from Thailand in the 1980s and maintained by the Bureau of Fisheries and Aquatic Resources and ICLARM; and an Egypt-Swansea strain originated from tilapia collected from Lake Manzala in 1979 and transferred to the Philippines by University College of Swansea in 1989. The extrapolated yields of the Thai and Egypt-Swansea strains were not significantly different from each other and averaged approximately 5,000 kg/ha/yr. The average extrapolated yield of the FAC strain was only 2,389 kilograms per hectare per year (kg/ha/yr), which probably reflects the introgression of O. mossambicus. Researchers also compared the yield of Egypt-Swansea fish grown in ponds fertilized at two different rates of nitrogen and phosphorus fertilization, observing no significant difference between the two rates.

United States - Data Analysis and Synthesis

The Data Analysis and Synthesis Team (DAST) at the University of California, Davis (UCD) is developing a preliminary model to investigate the effects of integrated aquaculture and agriculture on nutrient cycling and whole system productivity. The model will concurrently evaluate the impacts of various management actions for enhancement of pond sediment quality. The model consists of three modules: fishpond, crop, and terrestrial soil nitrogen. Inputs of nitrogen into the pond include feed and/or fertilizer and water. Outputs from the pond include uptake by fish, effluent water, and removal of pond sediments. The three modules are linked through the use of sediment from ponds as crop fertilizer and/or the use of wastes from crops as feed/fertilizer to aquaculture ponds. Preliminary results demonstrate that feed quality and digestibility of feed need to be considered to improve overall estimation of organic matter and nitrogen production in the fish pond, and to improve estimation of fish growth.

Researchers at OSU continued work on model refinement in the decision support system POND© (Version 2.5). These models allow users to simulate pond aquaculture facilities at three levels of complexity. At Level 1, models are geared toward applied management and rapid analysis of pond facilities. Simulation results agree reasonably well with observed data under a wide range of culture conditions, suggesting that the models used at this level are relatively robust and will likely be useful for a diverse audience, including pond managers, planners, and educators. The water temperature model in POND© has been validated by the use of CRSP data from Honduras, Rwanda, and Thailand. The fish bioenergetics model has also been calibrated for channel catfish, tambaquí, and pacu.

Level 2 models allow for more detailed pond analysis, management optimization and numerical experimentation. Plankton and nutrient dynamics in ponds are part of this model. Level 3 models explore in greater detail fundamental aspects of pond dynamics such as detailed nutrient transformations in pond water/sediments, and atmospheric diffusion.

A methodology to enable users to customize POND© for alternate culture species and locations has been incorporated directly into the software. Because of the high level of complexity of interactions among variables in the model, manually changing the parameters proved to be extremely time-consuming, limiting the use of the software for examining production potential for different pond culture species. An iterative, non-linear, adaptive search method (genetic algorithm or GA) for automatically generating new parameters for the fish growth model has been developed. Adequate convergence to acceptable parameter values was obtained for the three species (channel catfish, tambaquí and pacu) chosen to evaluate GA's as an effective parameter estimation technique.

Special Topics Research

A water temperature and dissolved oxygen model using stochastically- generated weather parameters is being developed. Currently, the model can be executed for an 85-day simulation. Prediction of temperature and dissolved oxygen match well with measured values, but algorithms to estimate fish growth and chlorophyll-a concentrations are still in development.

Special topics research included investigations into whether sex reversal of newly hatched tilapia may be accomplished by administering naturally occurring sources of testosterone obtained from frozen bull testes as an alternative to using 17-a methyltestosterone (MT), a synthetic androgen which is also an anabolic steroid.