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PD/A CRSP Aquanews-Winter 2001
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Notices of Publication

These Notices of Publication announce recently published work carried out by PD/A CRSP participants. To receive a full copy of a report, please contact the author(s) directly unless it is otherwise noted.

CRSP Research Report 00-162

Bio-energetic modeling of growth and waste production of Nile tilapia (Oreochromis niloticus L.) in recirculation systems

M.C.J. Verdegem and A.A. van Dam
Fish Culture and Fisheries Group
Department of Animal Sciences
Wageningen University
P.O. Box 338, 6700 AH Wageningen, The Netherlands

A.A. Cabarcas-Nuñez
Department of Marine Sciences
University of Puerto Rico
P.O. Box 9013
Mayagüez, PR 00681-5000 USA

L. Oprea
Fishing and Aquaculture Department
University of Galati "Dunarea de Jos," Domneasca Str. 47
6200 Galati, Romania

A bio-energetic fish growth simulation (FGS) model was developed for Clarias gariepinus and subsequently adjusted for the culture of Oreochromis niloticus, Oncorhynchus mykiss and Colossoma macropomum. The FGS model was extended with a fish waste module (FWM) to calculate the total waste production due to feeding by tilapias grown in indoor recirculation systems. Wastes calculated included the amount of uneaten feed, feces and NH4+ production. The amounts of wastes produced were expressed as g nitrogen (N). The model was calibrated and validated using 3 independent data sets, together comprising 175 aquarium experiments, monitoring growth in all cases and changes in proximate body composition of O. niloticus between stocking and harvesting in 51 cases. Fishes were grown in the individual weight range of 1– 290 g using 32-54 % protein diets and feeding levels between 5 and 35 g kg-0.8 d-1. The principal read-out parameters for calibration and validation of the model were final weight and final body fat level. Because waste production is the result of the same metabolic processes that lead to protein and fat deposition, it was assumed that waste production was simulated well when protein and fat deposition are. The calibrated model was used to review the effect of feeding level and dietary protein level on N-waste production per kg tilapia produced. Finally, tilapias were grown in 2 different types of recirculation systems and stagnant water ponds, quantifying N-inputs and the amount of N-wastes recovered from each system. The latter was defined as the sum of N-waste discharged (sludge and sludge water drained) and within system accumulation of N-wastes (organic and inorganic nutrients) during culture. After model calibration, the agreement between simulated and observed final weight and body fat level for all data sets was visualized. In recirculation systems different types of N-wastes were estimated well by the model. Care must be taken when applying the model to pond systems. More insight is needed on feeding ecology of tilapias in these systems.

This abstract was excerpted from the original paper, which was published in K. Fitzsimmons and J. Carvalho Filho (Editors), Tilapia Aquaculture in the 21st Century, Fifth International Symposium on Tilapia Aquaculture. American Tilapia Association and Departamento de Pesca e Aqüicultura/Ministério da Agricultura e do Abastecimento, Rio de Janeiro, Brazil, pp. 368–381.


CRSP Research Report 00-163

A pilot study on the spatial and temporal soil moisture distribution in integrated crop-fish-wetland and crop-wetland agroecosystems in Zomba-East, Malawi

Daniel Jamu
International Center for Living Aquatic Resources Management
P. O. Box 229, Zomba, Malawi.

Integration of aquaculture into existing agricultural systems has been reported to improve productivity and ecological sustainability through better water management, improved soil fertility arising from waste recycling and synergies occurring between the aquaculture and agricultural components, and extension of the crop growing season. While information is available on the role of integrated systems in improving soil fertility and waste recycling, quantitative data on the influence of fishponds on the length of the crop growing season, and the temporal and spatial distribution of soil moisture around fishponds is not available. I therefore quantified the influence of fishponds on soil moisture regimes on six farm systems in Zomba district by comparing the spatial and temporal distribution of soil moisture between farm subsystems with fishponds (integrated crop-fish-wetland) with that from adjacent sites without fishponds (crop-wetland). Four sampling transects, each with five sampling sites placed at 2, 4, 6, 8 and 10m from the pond dike were established at four cardinal points of the pond. Soil samples were obtained biweekly from each sampling site for gravimetric soil moisture determination. Sampling was terminated when soil moisture content fell below the permanent crop wilting point, which for this study was 13%. A similar procedure was adopted for the crop-wetland subsystem; however, a predetermined axis in the subsystem was used as a reference point for the placement of transects. Soil moisture content was measured gravimetrically. A paired t-test was used to determine differences in soil moisture content between the integrated crop-fish-wetland and crop-wetland subsystem. The length of the crop-growing season was defined as the period during which soil moisture content was above the permanent wilting point and below field capacity (23% moisture content). One-way ANOVA was used to determine significant differences (P< 0.05) in the spatial distribution of soil moisture between the four cardinal points of each subsystem. Significant differences (P< 0.05) in soil moisture content between the two subsystems were detected at five of the six farms sampled. At two of the sites where significant differences were detected, the crop-wetland subsystem had significantly higher soil moisture content than the integrated crop-fish-wetland subsystem. Placement of a fishpond in a seasonal wetland did not influence the length of the crop-growing season. These initial results appear to suggest that although integration of fishponds in crop-wetland systems may significantly affect soil moisture regimes, these differences are not important in so far as the extension of the crop-growing season is concerned. Since the study used a small sample size and soil samples from the top 15cm of the soil, and the fishpond may influence soil moisture below this zone, further studies that incorporate more farms and sample at depths greater than 15cm are needed before definitive conclusions on the influence of fishponds on soil moisture regimes in seasonal wetlands are drawn.

This abstract was excerpted from the original paper, which was published in K. Fitzsimmons and J. Carvalho Filho (Editors), Tilapia Aquaculture in the 21st Century, Fifth International Symposium on Tilapia Aquaculture. American Tilapia Association and Departamento de Pesca e Aqüicultura/Ministério da Agricultura e do Abastecimento, Rio de Janeiro, Brazil, pp. 582–587.


CRSP Research Report 00-164

Evaluation of tilapia culture by resource limited farmers in Panama and Guatemala

Leonard L. Lovshin
Department of Fisheries and Allied Aquacultures
Auburn University, Al 36849 USA

Mixed-sex and male Nile tilapia, Oreochromis niloticus, were cultured in family and communally managed fish ponds in Guatemala and Panama in the 1980s. Fish were used to improve family nutrition and meager incomes of the pond managers. Tilapia culture systems were designed to permit farmers with no fish culture experience to produce their own tilapia fingerlings on-farm and grow the fingerlings using available household by-products and animal manures to sizes required for home consumption and sale. The author returned to Guatemala and Panama in 1998 to evaluate the ability of pond managers to learn and sustain tilapia culture as a farm activity.

Mixed-sex culture of Nile tilapia was the culture system introduced to Guatemalan pond managers in the 1980s and continues as the only culture system employed by those farmers still growing fish. Forty-three percent of the pond projects were abandoned between 1989 and 1998. Seventy-two percent of Guatemalan farmers produced small tilapia for pond stocking on-farm or obtained them from neighbors. Use of the predacious guapote tigre, Cichlasoma managuense, to control tilapia offspring in grow-out ponds increased from 14% in 1989 to 36% in 1998.

Pond managers in Panama were shown how to grow either mixed-sex Nile tilapia with the guapote tigre or monosex male Nile tilapia to reduce tilapia offspring during grow-out and permit harvest of a 200 to 400 g fish. Twenty-nine percent of the pond projects polycultured mixed-sex tilapia with a predator and 71% grew male tilapia in 1984. Forty-eight percent of the pond projects were abandoned between 1984 and 1998. Of the projects still culturing tilapia in 1998, 36% cultured mixed-sex tilapia with a predator and 64% cultured male tilapia. Sixty-four percent of the projects still growing fish in 1998 stocked guapote tigre, indicating that some of the projects stocking male tilapia were also stocking guapote to control tilapia offspring. Most pond managers did not produce tilapia fingerlings on-farm as 82% of the fish pond projects received their tilapia fingerlings from the government hatchery.

Economic and nutritional impacts from fish culture as documented for Panama in 1984 and Guatemala in 1989 were not sustained. The failure of fish culture in Guatemala and Panama does not rest solely with tilapia but with a complex of economic, social, technical and political issues hat combined to limit the intended impact of fish culture on impoverished pond managers and their families.

This abstract was excerpted from the original paper, which was published in K. Fitzsimmons and J. Carvalho Filho (Editors), Tilapia Aquaculture in the 21st Century, Fifth International Symposium on Tilapia Aquaculture. American Tilapia Association and Departamento de Pesca e Aqüicultura/Ministério da Agricultura e do Abastecimento, Rio de Janeiro, Brazil, pp. 633–638.


CRSP Research Report 01-165

Masculinization of Nile tilapia with steroids: Alternate treatments and environmental effects

W.M. Contreras-Sánchez, M.S. Fitzpatrick,
and R.H. Milston
Department of Fisheries and Wildlife
Oregon State University
Corvallis, OR 97331-3803

C.B. Schreck
Oregon Cooperative Fish and Wildlife Unit
Biological Resoures Division - USGS
Corvallis, OR 97331-3803

Steroid-treated food is widely used to masculinize tilapia. We have previously shown that short-term immersion in steroids can also masculinize Nile tilapia. In the following study, we determined that a single immersion of tilapia fry in Trenbolone Acetate for 3 hr on 12, 13, or 14 days post-fertilization (dpf) or multiple immersions in combinations of days between 12 and 15 dpf, can result in masculinization. However, effectiveness of immersion treatment varied between experiments, suggesting that sensitivity to treatment may differ between individual broods. We also found that the use of 17a-methyltestosterone (MT)-treated food to masculinize Nile tilapia results in accumulation of MT in sediments even after cessation of treatment.

This summary was excerpted from the original paper, which was published in B. Norberg, O.S. Kjesbu, G.L. Taranger, E. Andersson, and S.O. Stefansson (Editors), Proceedings of the 6th International Symposium on the Reproductive Physiology of Fish. Institute of Marine Research and University of Bergen, Bergen, pp. 250–252.


CRSP Research Report 01-166

Managing the accumulation of organic matter deposited on the bottom of shrimp ponds . . . Do chemical and biological probiotics really work?

Stanislaus Sonnenholzner
Fundación CENAIM-ESPOL (Centro Nacional de Acuicultura e Investigaciones Marinas-Escuela Superior Politecnica del Litoral)
PO Box 09-09-4519
Guayaquil, Ecuador

Claude Boyd
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, AL 36849 USA

Accumulation of organic matter increases oxygen demand and the development of reducing and acidic conditions in bottoms soils. Deterioration of soil and water quality in aquaculture systems is often associated with decomposition of organic matter over time. Several commercial products currently used in shrimp ponds in Ecuador to accelerate decomposition of organic matter during the fallow period were evaluated. Two ponds were used, one with a salinity of 10–20 ppt and the other with 30 ppt. Soil respiration rates were evaluated in situ and in the laboratory. Each treatment was replicated four times. All experiments resulted in a similar drop in soil pH, although differences in soil moisture content occurred for the different evaluations. No statistical differences were found among treatments. No benefits were found by applying bacterial inocula or enzymatic suspension to enhance the decomposition of organic matter during fallow periods. Failure of probiotics to enhance organic matter decomposition probably resulted because soils were not extremely high in organic matter content or deficient in microorganisms or extracellular enzymes.

This abstract was based on the original paper, which was published in World Aquaculture, 31(3):24-28.


CRSP Research Report 01-167

Environment, aquaculture, and food policy nexus: Case study of two USAID aquaculture projects in Rwanda

Hillary Egna
Pond Dynamics/Aquaculture
Collaborative Research Support Program
Oregon State University
418 Snell Hall
Corvallis, OR 97331 USA

This case study centers on some of the institutional networks that evolved in Rwanda around aquatic food resources and how these networks acted as microcosms of the larger system being played out at the national level. The majority of aquaculture activity throughout the 1980s was led by two US Agency for International Development funded projects, the Pond Dynamics/Aquaculture Collaborative Research Support Program and an extension project, the Projet Pisciculture Nationale. Changes brought about by project networks became embedded in Rwanda’s cultural, economic, and political structures. Through 15 years of promotion by donors, nontraditional farming technology was gaining a foothold in Rwanda. The case study demonstrates that institutional networks arose not through organizational preplanning but by default. This resulted in few of the planned objectives being as successful as unanticipated outcomes, such as the emergence of women as new technology adopters, the development of a highly successful water quality laboratory, and the inclusion of aquaculture into national policy. Many of the unanticipated results derived from the efforts of expatriates, who promoted aquaculture both actively and passively. While the expatriates were effective, the study questions whether a few external actors should accumulate so much power and influence over development agendas.

This abstract was based on the original publication, a chapter published in D.L. Soden and B.S. Steel (Editors), Handbook of Global Environmental Policy and Administration. Marcel Dekker, Inc., New York, pp. 281–314.


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