Raul H. Piedrahita, Department of Agricultural Engineering and Aquaculture and Fisheries Program, University of California, Davis, California 95616, U.S.A.
15 March 1992, CRSP Research Reports 92-41
Abstract This study examined possible changes in dissolved oxygen concentration
resulting from various short-term management actions that can be undertaken
in response to cloudy conditions. The management actions were examined with
a computer model of water quality in a pond, and include nutrient enrichment
(fertilization, pH adjustment), water level control, and water exchange.
Results of these simulations indicated that general management strategies
directed at increasing nutrient availability were the least effective in
counteracting the effect of the increased cloud cover. Flushing and reducing
the water level in the pond were considerably more effective short-term
management actions. Areas for field research were suggested to confirm the
effectiveness of the various strategies.
This abstract was reprinted from the original which was published in Journal of the World Aquaculture Society, 1991, 22:157-166.
David R. Teichert-Coddington, Bartholomew W. Green, and Ralph W. Parkman, Department of Fisheries and Allied Aquacultures, Auburn University, Alabama 36849 USA
15 March 1992, CRSP Research Report 92-42
Abstract Two experiments were conducted in Choluteca, Honduras, to asertain effects on yield and profitability of partial substitution of chicken litter for feed during initial growth of semi-intensively cultured penaeid shrimp. In the first experiment, four management strategies based on various combinations of chicken litter (60 kg/hectare per week, total solids) and prepared feed were tested. After 99 days of growth, shrimp yield was not increased significantly by manuring in addition to feeding, and chicken litter was not profitably substituted for feed during the first 4 to 8 weeks. Mean total yields for the nonsubstitution treatments were 7 to 41% greater than those for treatments in which chicken litter was partially substituted for feed, and net income for the nonsubstitution treatments was 27 to 58% greater than that for substitution treatments. Differences were not significant (P>0.05) because of large yield variation resulting from variable survival. In the second experiment, two combinations of chicken litter at higher rates and prepared feed were tested. Low-cost chicken litter applied weekly at 220 kg/hectare was profitably substituted for high-cost feeds during the first 8 to 9 weeks of grow-out. However, chicken litter applied at low rates is an ineffective substitute for feed and would not improve yields if applied with feeds.
This abstract was reprinted from the original which was published in The Progressive Fish-Culturist, 1991, 53:150-156.
C. F. Knud-Hansen, Asian Institute of Technology, Agriculture and Food Engineering, G. P.O. Box 2754, Bangkok 10501, Thailand
C.D. McNabb and T. R. Batterson, Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan 48824, U.S.A.
15 April 1992, CRSP Research Report 92-43
Abstract In most waste-fed systems, water quality degradation ultimately limits net fish yields (FY). Often as fertilization rates increase, inefficient nitrogen utilization together with daytime pHs exceeding 9.0 results in high unionized ammonia concentrations which reduce fish growth and survival. FY generally increases until high unionized ammonia concentrations and/or low morning dissolved oxygen concentrations become growth limiting. For optimal fish yields, maximum food availability must be balanced with favorable pond water quality. This paper examines the role of nitrogen limitation in managing pond eutrophication in order to produce greater and more predictable fish yields.
This abstract was excerpted from the original paper, which was published in the Proceedings of the International Association of Theoretical and Applied Limnology 24:2541-2543, 1991.
Kevin Hopkins, College of Agriculture, University of Hawaii at Hilo, Hilo, Hawaii 96720, U.S.A.
Amararatne Yakupitiyage, Asian Institute of Technology, Agriculture and Food Engineering, G. P.O. Box 2754, Bangkok 10501, Thailand
15 April 1992, CRSP Research Report 92-44
Abstract Seine sampling is widely recognized by aquaculturists to produce upwardly-biased estimates of size. This bias is sometimes given as a reason for not including sampling data collected by seining when analyzing growth (i.e., only stocking and harvest data are used). Fisheries biologists recognize that many fish sampling methods produce biased size estimates, and considerable effort is expended to correct for bias, e.g., mesh selection curves. Aquaculturists, on the other hand, tend to either ignore the bias or, worse, ignore the supposedly biased data. This paper quantifies the degree of bias in size estimates of Nile tilapia (Oreochromis niloticus) that were obtained from seine samples. Additionally, the effects of fish size and sample size on precision of size estimates from seine samples are quantified. These quantifications are based on comparisons of seine sample data collected the day before harvest and the fish size at harvest.
This paper was published as a note in the Journal of the World Aquaculture Society 22:260-262, 1991.
Carole R. Engle, University of Arkansas at Pine Bluff, PineBluff, Arkansas 71601, U.S.A.
Michael Skladany, Michigan State University East Lansing, Michigan 48824, U.S.A.
May 13 1991, CRSP Research Reports 92-45
Abstract The Pond Dynamics/Aquaculture CRSP has conducted basic research since 1983 on the biological and chemical factors that influence fish production. The goal of these studies is the improved well-being of farmers that adopt new aquaculture technologies. The ultimate test of the value of the research results generated is if farmers themselves demonstrate the economic benefit by incorporating new technologies into their farming systems. Therefore, economic analysis of the costs and benefits to the farmer of the various technologies developed will provide insight into the value of these technologies to farmers.
This abstract was excerpted from the original article which was published as CRSP Research Report 92-45 by the Program Management Office of the Pond Dynamics/Aquaculture Collaborative Research Support Program (PDA/CRSP).
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