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PD/A CRSP Aquanews-Winter 2003

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Notices of Publication

his Notice of Publication announces recently published work carried out under PD/A CRSP sponsorship. To receive a full copy of a report, please contact the author(s) directly.

CRSP Research Report 03-186

EVALUATION OF NILE TILAPIA POND MANAGEMENT STRATEGIES IN EGYPT

B.W. Green
Department of Fisheries and Allied Aquacultures
Auburn University, AL 36849-5419, USA

Z. El Nagdy and H. Hebicha
Central Laboratory for Aquaculture Research
Agricultural Research Center
Abbassa, Abou Hammad
Sharkia, Egypt

Abstract

Five pond management strategies for Nile tilapia Oreochromis niloticus L. production were evaluated in 0.1-ha earthen ponds in Egypt during a 145-day production cycle. Pond management strategies developed by the Pond Dynamics/Aquaculture Collaborative Research Support Programme (PD/A CRSP) were compared with a traditional and a modified Egyptian pond management strategy. Young-of-year Nile (mixed-sex or sex-reversed) tilapia were stocked into ponds at 20 000 fish ha-1. Sex-reversed tilapia were stocked into chemical fertilization, organic fertilization plus formulated feed and feed only treatment ponds, whereas mixed-sex tilapia were stocked into organic fertilization plus formulated feed and chemical plus organic fertilization plus formulated feed treatment ponds. Nile tilapia yields ranged from 1274 to 2929 kg ha-1. Nile tilapia yields in organic fertilization plus formulated feed treatments were significantly greater than the yield from chemical fertilization ponds. PD/A CRSP pond management strategies did not produce significantly greater Nile tilapia yields than the traditional Egyptian system, but a larger percentage of harvested tilapia in the organic fertilization plus feed treatments were classified in the first and second class size categories compared with the traditional Egyptian system. Organic fertilization plus formulated feed pond management strategies had the highest net returns, average rate of return on capital and the highest margin between average price and break-even prices to cover variable costs or total costs.

This abstract was based on the original paper, which was published in Aquaculture Research, 33 (2002):1037–1048.
CRSP Research Report 03-187

TECHNIQUES TO MITIGATE CLAY TURBIDITY PROBLEMS IN FERTILIZED EARTHEN FISH PONDS

Yang Yi and C. Kwei Lin
Aquaculture and Aquatic Resources Management
Agricultural and Aquatic Systems and Engineering Program
School of Environment, Resources, and Development
Asian Institute of Technology
PO Box 4, Klong Luang
Pathumthani 12120, Thailand

James S. Diana
School of Natural Resources and Environment
University of Michigan
Ann Arbor, MI 48109-1115, USA

Abstract

An experiment was conducted in fifteen earthen ponds at the Asian Institute of Technology (AIT), Thailand, during June to November 1998 to identify the source of clay turbidity mitigation techniques and their effects on fish growth and water quality, and to find a suitable approach for turbidity mitigation during the rainy season. There were five treatments: (A) control; (B) covering upper 50 cm pond dikes with black plastic material to prevent turbidity from run-off (edge-covered); (C) covering pond bottoms with small mesh (1 cm) net to prevent turbidity from fish disturbance (bottom-covered); and (E) covering pond dikes with rice straw (straw-covered). All ponds were fertilized weekly with chicken manure at a rate of 500 kg ha-1 (dry matter basis) supplemented with urea and triple superphosphate (TSP) to provide 28 kg N per ha per week and 7 kg P per ha per week. Sex-reversed all-male Nile tilapia (Oreochromis niloticus) were stocked at two fish per square meter at a size of 19.0±1.0 g. Results showed clearly that clay turbidity was mainly from the run-off of pond dikes but not from fish disturbance of pond bottom during the rainy season and indicated that covering pond dike was effective in mitigating clay turbidity caused by the run-off in fish ponds. No significant differences of fish survival were found among all treatments. The straw- and weed-covered treatments resulted in significantly higher fish growth and yield. In contrast, the edge- and bottom-covered treatments did not increase fish yield, compared with the control. Covering pond dikes with rice straw not only reduces clay turbidity caused by run-off but also enhance Nile tilapia growth probably through microbial biofilm developed on the rice straw. Therefore, covering pond dikes with rice straw is a cost-effective technique for clay turbidity mitigation in fish ponds during the rainy season.

This abstract is escerpted from the original paper, which was published in Aquacultural Engineering, 27 (2003):39–51

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