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Summary of Activities and Accomplishments

II. Summary of Activities and Accomplishments


Major accomplishments during this reporting period include the initiation of Seventh Work Plan studies at all sites. Studies scheduled under the Sixth Work Plan had been concluded in the previous period, except for one experiment, which had been exchanged with a Seventh Work Plan experiment. POND, the new decision-support system which allows facility managers to project economic returns of various management strategies, is now available to interested persons. A number of special Topics Research activities were completed. The CRSP also participated in two different evaluations. Honduras, Thailand, the DAST, and the Management Entity participated in the overall CRSP review. The Egypt project underwent a technical review and was subsequently granted an extension. As always, efforts to disseminate research results continued through a variety of avenues.

Overseas Research


Seventh Work Plan experiments were initiated this year at the brackish water site at Choluteca and at the freshwater site at El Carao. Brackish water research focused on the environmental effects of shrimp farming on estuarine water quality and on the development of culture techniques to reduce environmental impact. Researchers demonstrated that riverine estuaries were associated with higher nutrient loads than gulf embayments. Non-riverine estuaries showed no seasonal variability; however, riverine estuaries showed seasonal variability, and exhibited higher nutrient concentrations in the dry season. A companion study found that shrimp producers could reduce the nutrient input into estuaries during the dry season by a modification in management practices. It was found that use of fertilizer in the dry season did not increase shrimp yield. Other input rates can also be reduced in the dry season because decreasing the feeding rate by up to 50% did not result in significantly reduced shrimp yield.

Global Experiment research was carried out at El Carao with scientists comparing different management regimes. The first treatment followed the fertilization recommendations obtained from the decision-support system PONDCLASS (the precursor to POND), and was compared with a second treatment which used total ammonia concentrations (TAN) as a fertilization guideline. A third treatment compared the effect of increasing the stocking rate from 2 to 3 fish/m2. PONDCLASS recommendations led to excessive nitrogen fertilization, because primary productivity was constrained by a carbon limitation. The results for the TAN experiment were inconclusive. Almost identical fish yields were obtained with the two different stocking rates. However, individual fish size was smaller at the higher density which significantly reduces marketability of the tilapia.

A second freshwater study combined various ratios of tilapia and tambaqui in a polyculture experiment. A combination of 75% tilapia and 25% tambaqui’ was found to give the best results. The Honduras team also conducted two studies which were not part of the Sixth or Seventh Work Plan. Hormonal sex-reversal is a commonly practiced method to obtain monosex fish populations. Determination of the optimal water temperature regime for mass production of tilapia fry for hormonal sex-reversal was the goal of the first investigation. Using a threshold temperature of 15 degrees C, fry production did not occur below 140 degree-days; the upper boundary was given by 195 degree-days. In a companion study, researchers tried to determine if the administration of 17a-methyltestosterone improved the growth of treated fry and fingerlings. This side-effect has been reported in the literature for other species; however, after 150 days no significant differences were observed between treated and untreated fry in this experiment.


Rwanda CRSP personnel conducted five workshops in late 1993 and trained 60 extension agents of the National Fish Culture Service. The terrible civil war that has ravaged Rwanda since spring 1994 ended all research and extension activities in Rwanda. When the civil strife erupted, the Rwanda CRSP team was investigating the productivity difference of fed and non-fed ponds at different elevations; the determination of fish production relationships from existing farmer-generated data; and tilapia fry mass-production techniques. These developments necessitated the development of a new work plan for the Rwanda research group. Replacements have been developed for those experiments which were underway in Rwanda at the outbreak of open hostilities. All hope of regaining access to the Rwanda data has been lost. New studies have been initiated to determine the most effective lime requirement estimators for broadly different soil types; to investigate the effect of pond soil characteristics on phosphorus fixation and availability; to determine the effect of feed consumption, growth, and conversion efficiency of tilapia fry; and to examine the efficacy of sex reversal treatment as a function of water temperature. These studies are still in progress. Results from a study on the use of defatted rice-bran as fish feed show that rice-bran, an agricultural by-product, is a good and economic supplemental food source, especially when pelleted. Pellets are not only easier to handle than loose rice bran, they also reduce the amount of fertilizer applications needed to maintain pond fertility.

Thailand and the Philippines

Determination of optimal phosphorus fertilization rates was the aim of two studies conducted by Thailand and CRSP researchers. The first study investigated the relationship between phosphorous sediment concentrations and phosphorous fertilization rates. It was found that optimum phosphorous fertilization, which does not result in either under- or over-fertilization, can be obtained if the fertilization rate is based on the phosphorous saturation level of the sediment. The second study reported a quick method to estimate phosphorous saturation level in sediment by using sediment clay content as the key variable.

Supplemental feeding is often necessary for growing larger, more valuable tilapia. Several studies investigated aspects of this management technique. Results indicated that early supplemental feeding produced inefficient feed use, while a late starting date (after fish have reached 150 g) extended the growing period considerably. A companion study investigated the relationship between stocking density and carrying capacity under a supplemental feeding regime. Initial results indicated that growth rates were similar among treatments and that carrying capacity had not been reached. A third investigation, comparing the growth rate of tilapia under different input regimes, found that 90.3% of the variance in growth could be explained by feed and fertilizer input, alkalinity, and total inorganic nitrogen concentration. Combinations of feed and fertilizer were most efficient in growing tilapia to 500 g.

Improved understanding of pond dynamics is key to optimizing production techniques. Carbon has been shown to be a limiting nutrient in previous PD/A CRSP research of tropical fish ponds. The Thailand research group worked on two studies to further investigate carbon dynamics. One study attempted to stabilize total alkalinity by adding carbonate as part of the fertilizer input. During the dry season, total alkalinity was stable in treatment ponds, but declined in control ponds. During the wet season, no treatment effect was observed. A second study, currently underway, will quantify the rates of exchange of carbon dioxide between pond water and the atmosphere and compare these rates with photosynthetic carbon uptake and respiratory release.

Most of the PD/A CRSP's work has been done in shallow ponds (approximately 1 m deep). However, there exists considerable potential for aquaculture in rain-fed irrigation reservoirs. These ponds would likely exhibit different characteristics which would require the development of new management strategies. The initial results of an analysis of the diel temperature and oxygen stratification in deep, rain-fed ponds in Thailand lends credence to this view. While the surface layer (up to 1 m deep) behaves much like a shallow pond, the water below this layer is isolated from the top layer and did not seem to mix during the experimental period.

Research conducted in the Philippines is a sub-project of the Thailand project. Two investigations are currently underway at the Freshwater Aquaculture Center. A comparison of the performance of different tilapia strains will provide the information necessary for development of a breeding program. The CRSP Philippine team is collaborating with ICLARM's "Genetic Improvement of Farmed Tilapia" (GIFT) project and with the research project of "Genetic Manipulations for Improved Tilapia" conducted by the Freshwater Aquaculture Center at Central Luzon State University and the University of Wales Swansea. Fish from both projects will be compared with the Chitralada strain, used in Thailand, and the unmanipulated strain used in the Philippines. The second study tests whether CRSP fertilizer guidelines will be socially acceptable and economically viable under Philippine conditions.


The beginning of experiments in Egypt last year was delayed due to inclement weather and a resulting fish kill; therefore, most of the second year experiments (see CRSP Work Plan 7) were still underway by the end of this reporting period. In order to conclude the research, the end date of the Egypt project was extended to December 31, 1994. Summaries of activities conducted from September to December 1994 will be published in the Final Report of the Egypt Project.

Investigations at the Central Laboratory for Aquaculture Research (CLAR) in Abbassa, Egypt, focused on validating CRSP guidelines in an arid climate. Five different pond management strategies were tested and yielded significantly different results. The highest gross yields were obtained from the Fertilization then Feed treatment; the lowest yields were obtained from the Chemical Fertilization treatment. A companion study examined the economic returns obtained from each treatment. The highest net economic returns were obtained from the Fertilization then Feed treatment, while the Chemical Fertilization treatment resulted in the lowest returns. A third study compared the yield characteristics of Nile tilapia to those of blue tilapia. Initial results indicate Nile tilapia performs better in every treatment than blue tilapia. A fourth investigation aims to determine the effect of stocking rate on Nile tilapia growth and yield. Initial results indicate no negative effects of the higher stocking rate on either growth or yield. The Egypt project team also initiated a study of Egyptian pond bottom soils to determine the role of pond soils in pond nutrient dynamics.

The Egypt Project added biotechnology research, a new line of inquiry in the family of CRSP studies. Several of the studies focused on the use of sex hormones, mainly 17a-methyltestosterone (MT), which is internationally used as a sex-reversing agent in aquaculture. The U.S. Food and Drug Administration (FDA) granted a "compassionate" Investigational New Animal Drug exemption (INAD) to allow research on the efficacy and safety of this drug. A field trial was started in July 1994 at the Central Laboratory for Aquaculture Research (CLAR) at Abbassa, Egypt. This research, conducted in the field at the CLAR, was devoted to both the development of a technology to mass produce tilapia fry for sex-reversal, and examining the effects of MT on treated fry. Initial results indicate both high efficacy and survival rates.

Other MT-related research was conducted at Oregon State University (OSU) and the University of Hawaii (UH). The OSU research team characterized a binding site for sex-reversing hormones in gonadal tissue of adult Nile tilapia, and also developed a receptor assay, a fast tool for screening the efficacy of newly developed sex inversion agents. Other research at OSU continues to follow this line of inquiry by studying gonadal development in tilapia. The OSU team is also developing a cryopreservation technique for sperm and determining if an alternative sex-reversal technique (immersion) might be safer than the currently used method (medicated feed).

Researchers at UH conducted a study on the separation of the sex-reversing effects of MT from the growth-promoting effects of this drug on two different species of tilapia. It was found that the growth rate of Oreochromis aureus was nearly twice the rate of O. mossambicus at each dose level, and in almost all treatments, MT-treated animals grew significantly better. A totally different approach to the generation of monosex tilapia has been applied by Auburn University researchers, who are working to develop a YY tilapia breeding program to generate monosex tilapia offspring that are not treated with hormones. So far, four possible YY supermales have been identified. However, males which produced more than 95% male progeny in the first mating did not consistently produce such frequencies of male offspring in consequent spawns.

Bioconversion and polyculture research, another focus of the Egypt Project, focuses on building a polyculture system suited to the conditions found in Egypt by utilizing currently unused pond system components such as aquatic weeds or snails as fish food. Initial results from the bioconversion experiments indicated the effectiveness of grass and black carp as control agents; however, considerable contamination of the treatment ponds with common carp and mullet restrict interpretation of these results. Polyculture experiments are still ongoing and no results were available by the end of this period.

Data Analysis and Synthesis

During this period, the OSU DAST team completed work of the decision-support system POND. POND was developed to provide the aquaculture community with a tool for rapidly analyzing warm water aquaculture systems, and to assist in developing optimal management strategies. POND can be used to set up pond facilities with different configurations and/or management strategies. Facility managers can use POND to project possible future economic return for different management options. Approximately 80 copies of POND Version 2.0 have been distributed to a wide audience including extension agents, educators, producers, and researchers.

The University of California at Davis DAST team concentrated its efforts on further improving existing models of oxygen dynamics and developing new models for stratified ponds. Current understanding of oxygen dynamics is hampered by insufficient information about diel respiration patterns. To collect the missing information, a respirometer has been developed for use in aquaculture ponds. Field tests showed that respiration rates change substantially over diel periods, with the highest rates occurring in late afternoon. Model development for stratified ponds focused on water temperature behavior. A computer model using stochastic inputs of solar radiation, wind direction, and wind speed has been developed. Simulations carried out for Thailand ponds showed that surface temperatures exhibited the largest temperature fluctuations in response to stochastic inputs.

Central Data Base

A Central Data Base continues to be maintained by the CRSP for the storage and retrieval of standardized records from the research sites. At the individual sites, data on physical variables (e.g., solar radiation, temperature, and rainfall) and chemical variables (e.g., water and soil chemical characteristics) are collected concurrently with biological measurements (e.g., primary productivity, fish growth, and fish production). Whereas the resulting sets of data are useful for site-specific studies, the compilation of all the individual data sets into the Central Data Base provides opportunities for many kinds of global analyses. Detailed standardized records such as those found in the CRSP Central Data Base are rare in the aquaculture literature. All data from research activities conducted under the First through Fourth Work Plans are already in the Central Data Base, which has continued to expand through the inclusion of new data generated under the Fifth and Sixth Work Plans.

In response to a decision reached by the Management Entity and Board of Directors, with input from the Technical Committee, Central Data Base functions were transferred from the Program Management Office to the University of Hawaii at Hilo in May, 1993. As the quantity of data generated by CRSP research has increased, so have the storage requirements. Consequently, during this reporting period, the database has been consolidated and storage requirements have been reduced by approximately 50%. In order to increase speed, utility, and user-friendliness of the database, a new program, FoxproTM, has been implemented. An additional advantage of FoxproTM is its ability to work with different platforms. A menu-driven interface for Macintosh and IBM-type computers is being developed. This allows the distribution of the entire database as a self-contained unit.

This new feature will greatly increase the utility of the Central Data Base to researchers outside those directly involved with the PD/A CRSP. The Central Data Base was designed to facilitate communications with other large data bases, such as the Tropsoils CRSP data base and ICLARM's FISHBASE, thereby creating opportunities for collaboration. Efforts continue to integrate the CRSP Central Data Base with ICLARM's FISHBASE. The Central Data Base can also serve as a storage and retrieval center for standardized data from any research site. CRSP scientists as well as scientists in the aquaculture community at large may contribute to and access the data base. Data are available on computer diskettes or in print as Pond Dynamics/Aquaculture Collaborative Research Data Reports.