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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.
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.
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.
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.
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.
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.
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.
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The Pond Dynamics/Aquaculture CRSP is funded under USAID Grant No. LAG-G-00-96-90015-00
and by
the participating US and Host Country institutions.
Questions for or about the Aquaculture CRSP? Comments about this site? Email ACRSP@oregonstate.edu.
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