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PD/A CRSP Research Reports 98-121 to 98-125

PD/A CRSP Research Reports 98-121 to 98-125

Masculinization of Nile tilapia (Oreochromis niloticus) by single immersion in 17a-methyldihydrotestosterone and trenbolone acetate

Wilfrido M. Contreras-Sánchez, Universidad Juarez Autonoma de Tabasco, Villahermosa, Tabasco, Mexico

Martin S. Fitzpatrick, Ruth H. Milston, and Carl B. Schreck, Oregon Cooperative Fishery Research Unit and, Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, USA

15 April 1998, CRSP Research Report 98-121

Abstract The production of single sex populations offers several advantages in tilapia aquaculture, including enhanced growth and prevention of unwanted reproduction. A number of androgens have been shown to masculinize various tilapia species, including 17a-methyltestosterone (MT; summarized by Pandian and Varadaraj 1990 for Oreochromis mossambicus); mibolerone (Torrans et al. 1988 with O. aureus); fluoxymesterone (Phelps et al. 1992 with O. niloticus); norethisterone acetate (Varadaraj 1990 with O. mossambicus); 17a-ethynyltestosterone (Shelton et al., 1981 with O. aureus); 17a-methylandrostendiol (Varadaraj and Pandian 1987 with O. mossambicus), and trenbolone acetate (Galvez et al. 1996 with O. niloticus). Aquaculturists usually administer hormones to fish through the diet, but this method is prone to inefficiencies such as uneven exposure to steroid due to the establishment of feeding hierarchies or the availability of supplemental feed from pond primary pro- ductivity. Immersion of tilapia fry in steroid solutions may be one way to achieve masculinization and avoid these inefficiencies. This technique is well-developed in salmonid aquaculture (Piferrer and Donaldson 1989; Feist et al. 1995); however, it remains largely experimental in tilapia culture. Most of the reported studies immersed tilapia fry in androgens for periods of over 1 week to 5 weeks (Varadaraj and Pandian 1987; Torrans et al. 1988). Recently, Gale et al. (1995) demonstrated that immersion for just three hours in 17a-methyldihydrotestosterone (MDHT) on two days resulted in masculinization of Nile tilapia. The study described below was undertaken to determine if these findings could be extended through examination of the effects of 1) rearing density on efficacy of MDHT immersion, 2) a single immersion in MDHT, and 3) immersion in another masculinizing androgen, trenbolone acetate (TBA).

This abstract was excerpted from the original paper, which was published in Tilapia Aquaculture. Proceedings from the Fourth International Symposium on Tilapia in Aquaculture, November 9-12, 1997, Orlando, Florida. NRAES-106:783-790.


A strategic assessment of the potential for freshwater fish farming in Latin America

James McDaid Kapetsky, Inland Water Resources and Aquaculture Service, FAO Fisheries Department and Shree S. Nath, PD/A CRSP, Department of Bioresource Engineering, Oregon State University, Corvallis, OR, USA

15 April 1998, CRSP Research Report 98-122

Abstract Marine and many inland fishery resources are heavily exploited or overexploited, and although there is potential for increasing production from inland fisheries through intensification, development of aquaculture holds the most promise in the long term for improving food security through increasing the supply of fish. Currently, inland aquaculture production in Latin America is insignificant compared with the output from inland and marine fisheries. Lack of good planning at the national level has been identified as a serious impediment to the development of aquaculture. Estimates of potential are scarce that are both comprehensive and comparable over large geographic areas. Accordingly, the objective of this study was to estimate the potential for warm-water and temperate-water fish farming in the fresh waters of Latin America in order to stimulate improved planning for aquaculture development at national levels, and at the same time to provide a tool to plan comprehensively for technical assistance activities by FAO and other national and international organizations.

The present study is patterned on an estimate of warm-water fish farming potential made for Africa. However, a number of refinements have been made, one of which is a fourfold increase in resolution (i.e., to 5 arc-minutes, equivalent to 9 km x 9 km grids at the equator), thereby making the results much more usable for assessing fish farming potential at the national level. Another refinement is that, for the first time, a bio-energetics model has been incorporated into a geographical information system (GIS) to predict fish yields over large geographic areas. A gridded water temperature data set was used as input to the bioenergetics model to predict numbers of crops per year for four species: Nile tilapia (Oreochromis niloticus), tambaqui (Colossoma macropomum), pacu (Piaractus mesopotamicus) and carp (Cyprinus carpio). By varying input levels and sizes at harvest, opportunities for two levels of commercial fish farming and for small-scale fish farming were identified.

In addition to the suitability of each 9 x 9 km grid cell for the production of the above-mentioned species, each grid cell was evaluated for a number of other factors important for fish-farm development and operation. These included urban market potential based on travel time proximity and population size of urban centres, potential for farm-gate sales based on population density, engineering and terrain suitability for pond construction using a variety of soil attributes, water loss from ponds due to evapo-ration and seepage, and availability of agricultural by-products as feed inputs based on crop potential. Commercial and small-scale aquaculture models were developed by weighting these factors using a multiple criteria evaluation procedure. Areas unavailable for inland fish farming development were identified by incorporating protected areas and large inland water bodies as constraints. Finally, the yield potential of each grid cell for each of the four species was analysed using the growth model together with the other factors in the commercial and small-scale models to show the coincidence of each class of suitability with each range of yield potential.

Potential for inland fish farming is high in continental Latin America. From 8% to 60% of the continental area scores from suitable to very suitable for small-scale farming of Nile tilapia and carp, respectively. In the same areas, from 0.9 to 1.7 crops/y of Nile tilapia and from 0.9 to 1.8 crops/y of carp can be realized by harvesting at modest weights. The most important factor for commercial fish farming--urban market potential--scores high across more than one-half of the continent. For Nile tilapia and carp, from 19% to 44% of Latin America rates from suitable to very suitable for commercial farming. From 1.2 to 2.4 crops/y of Nile tilapia and from 1.2 to 2.3 crops/y of carp can be realized on the same areas by feeding at 75% satiation and harvesting at a moderate weight. Tambaqui and pacu occupy an intermediate position in terms of the surface area that is suitable or very suitable for commercial farming. From 0.7 to 1.4 crops/y for tambaqui and from 1.0 to 2.0 crops/y for pacu can be achieved from areas that are suitable or very suitable for commercial farming by feeding at 75% satiation and harvesting at a moderate weight.

From a country viewpoint, at least 18 of the continental countries have some area with potential that rates suitable or very suitable for farming of Nile tilapia and pacu, while there are 19 in the same category for tambaqui. Finally, there are opportunities for carp farming in all 21 countries.

This abstract was excerpted from the original paper, A strategic assessment of the potential for freshwater fish farming in Latin America. COPESCAL Technical Paper. No. 10. Rome, FAO. 1997. 128 pp.


Experimental and commercial culture of tilapia in Honduras

David R. Teichert-Coddington and Bartholomew W. Green, Department of Fisheries and Allied Aquacultures, International Center for Aquaculture and Aquatic Environments, Auburn University, USA, 36849-5419

15 April 1998, CRSP Research Report 98-123

Abstract In 1983 the USAID-funded Pond Dynamics/Aquaculture Collaborative Research Support Program (PD/A CRSP) was initiated in Central America, focusing on increasing natural productivity and fish yields of static water ponds by developing new input regimes without using mechanical aeration. Forty-one semi-intensive tilapia pond management systems were developed and evaluated in Honduras. Ponds were managed semi-intensively; Nile tilapia (Oreochromis niloticus) stocking rates did not exceed 3/m2. Nutrient inputs used were inorganic phosphorus, various levels of organic fertilization, combinations of organic and inorganic fertilization, and combinations of fertilizers and feeds. All tilapia production systems were evaluated in terms of income above variable costs and net returns to land and management from enterprise budgets for 150-day growing cycles. Incomes above variable costs were positive for all systems except where phosphorus was the sole input, and in one instance where chemical fertilizer was the sole input. Negative returns to land and management were demonstrated for systems based only on inorganic fertilization or on weekly chicken litter inputs less than 1000 kg/ha when fish were stocked at 1/m2. In general, profitability was higher when the stocking density was 2/m2, indicating available resources were not being used by fish at low stocking density. Positive returns to land and management in fed systems were obtained only at stocking rates of 2/m2. Fertilization was more profitable than feeding at low fish stocking rates. Greatest tilapia yields (5300 kg/ha for 150 days) were obtained with feeds, but a combination of chicken litter and nitrogen yielding 3700 kg/ha proved to be at least as profitable. Feed use was more profitable if feed requirements were reduced by substi- tution with chicken litter. If a large fish (> 300 gram) is required by the market, then feed will probably have to be used as a finisher. Production of 600-900 gram fish for the export market requires high quality feeds. Current practices in commercial intensive tilapia production practices in Honduras are described.

This abstract is excerpted from the original journal article which was published in Tilapia Aquaculture in the Americas, Vol. 1. World Aquaculture Society, Baton Rouge, Louisiana, B.A. Costa-Pierce and J.E. Rakocy (editors), 1997:142-162.


Small-scale fish farming in Rwanda: Economic characteristics*

Nathanael Hishamunda, Department of Agricultural Economics and Rural Sociology, Auburn University, AL 36849-5419

Maria Thomas, Work/Study Program, Tuskegee University, Tuskegee, AL 36088

David Brown, Humphrey High School, Humphrey, AR 72073

Carole Engle, Department of Aquaculture and Fisheries, University of Arkansas at Pine Bluff, Pine Bluff, AR 71611

Curtis Jolly, Department of Agricultural Economics and Rural Sociology, Auburn University, AL 36849-5419

15 July 1998, CRSP Research Report 98-124

Abstract A survey was conducted of 156 cooperative and 111 individual Rwandan fish farmers to estimate the costs and returns of aquacultural and agricultural crops. Enterprise budgets were developed for both individually and cooperatively produced fish, sweet potatoes, Irish potatoes, cassava, taro, sorghum, maize, peas, beans, soybeans, peanuts, rice, and cabbage. With the exception of Irish potatoes, all enterprises showed positive income above variable costs and positive net returns to land, labor, and management. Fish production yielded the highest income above variable costs and the highest net returns if fingerlings could be sold. If only food fish could be sold, cabbage was the most profitable crop. Sweet potatoes produced the highest yield of carbohydrates and soybeans were the least expensive source of protein. This study demonstrated that the cash income per unit of land generated by fish production is superior to other crops raised in the marais in Rwanda. While aquaculture is often considered a source of animal protein for household consumption, a high potential also exists for cash income generation.

This abstract was excerpted from the original article which was published as CRSP Research Report 98-124 by the Information Management and Networking Component of the Pond Dynamics/Aquaculture Collaborative Research Support Program (PD/A CRSP).

* The full version of this report is available as a 120 K Acrobat file. It can also be ordered in hard copy format.


Small-scale fish farming in Rwanda: Data report*

Nathanael Hishamunda, Department of Agricultural Economics and Rural Sociology, Auburn University, AL 36849-5419

Maria Thomas, Work/Study Program, Tuskegee University, Tuskegee, AL 36088

David Brown, Humphrey High School, Humphrey, AR 72073

Carole Engle, Department of Aquaculture and Fisheries, University of Arkansas at Pine Bluff, Pine Bluff, AR 71611

Curtis Jolly, Department of Agricultural Economics and Rural Sociology, Auburn University, AL 36849-5419

15 July 1998, CRSP Research Report 98-124a

Abstract This data report presents information collected in a survey of 267 fish farmers in Rwanda in September 1991. The findings are discussed in CRSP Research Report 98-124 entitled, "Small-Scale Fish Farming in Rwanda: Economic Characteristics" (Hishamunda et al., 1998). The Research Report contains enterprise budgets for individual and cooperative enterprises that raised fish and alternative crops. These enterprise budgets demonstrate that fish production yielded the highest net returns to land, labor, and management. Additionally, the Research Report compares the carbohydrate yield and protein costs of fish with those of alternative crops, and concludes that sweet potatoes produced the highest yield of carbohydrates and that soybeans were the least expensive protein source. The results of the study demonstrate that fish culture is a superior production system in terms of cash income per unit of land when compared with other crops raised in the marais, or valley lowlands, in Rwanda. This data report presents information collected in the survey that, while supplemental to the original research objectives, may be of interest. Section 1 contains 15 tables and 3 figures, which summarize the supplemental data collected by the survey instrument. The questionnaire itself comprises Section 2. Section 3 contains the criteria which were used to classify survey responses as unreliable, factors for converting various measures of crops and inputs into kilograms, and secondary data from the literature which were used to compare the nutritional values of various crops in the Research Report. Sources of secondary data used in the study are listed in the Literature Cited section.

This abstract was excerpted from the original article which was published as CRSP Research Report 99-124a by the Information Management and Networking Component of the Pond Dynamics/Aquaculture Collaborative Research Support Program (PD/A CRSP).

* The full version of this report is available as a 358 K Acrobat file. It can also be ordered in hard copy format.


Experimental and commercial culture of tilapia in Honduras

Abdelmoez A. F. Abdalla, Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan 48823

Clarence D McNabb, Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan 48823

15 October 1998, CRSP Research Report 98-125

Abstract This study investigated the acute effects of un-ionized ammonia (NH3-N) on 11 g fingerlings of Nile tilapia Oreochromis niloticus at two temperatures (23 and 33°C); and at 28°C with two sizes of fish, 3 and 45 g. In addition, sublethal effects of un-ionized ammonia on growth of Nile tilapia at 28°C were evaluated. All tests were conducted in flow-through bioassay system.

In acute toxicity tests at 23 and 33°C, the 96-h LC50's (±SD) were 2.25 ± 0.07 and 2.51 ± 0.16 mg/L NH3-N, respectively. There was not a significant effect between the two temperatures on acute toxicity of NH3-N in these tests (P 0.05). Estimates of the 96-h LC50's (±SD) at 28°C were 1.36 ± 0.45 mg/L NH3-N for the small fish and 2.65 ± 0.09 mg/L NH3-N for the large fish. In these tests, there was a significant difference between the two sizes of fish tested (P 0.05). In 35-day study of the effects of sublethal concentrations of NH3-N at 28°C, there was a linear decrease in fish weight gain with increasing un-ionized ammonia concentrations (r2 = 0.90, P 0.001). The concentrations of un-ionized ammonia that cause no reduction in growth, 50% reduction in growth, and 100% reduction in growth were 0.06, 0.73, and 1.46 mg/L NH3-N, respectively. These data suggest that Nile tilapia has tolerance to un-ionized ammonia similar to that of tilapia species, somewhat greater than that of channel catfish, and greater than that of many other warmwater fish and salmonids.

This abstract was excerpted from the original paper, which was published in D. Randall and D. MacKinlay (Editors), Nitrogen Production and Excretion in Fish. International Congress on the Biology of Fish, Symposium Proceedings, July 27-30 1998, pp. 35-44.


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