ARCHIVAL WEBSITE
You are viewing the archived website of Pond Dynamics / Aquaculture CRSP. When using this website, please understand that links may be broken and content may be out of date. You can view more information on the continuation of PD/A CRSP research archived at AquaFish Innovation Lab.
Aquanewswinter20048
Page 8 < PrevNext >
Notices of Publication announce recently published work carried out under Aquaculture CRSP sponsorship. To receive a full copy of a report, please contact the author(s) directly.
image3.gif
Notice of Publication
CRSP Research Report 03-196

Minimizing Environmental Impacts and Reuse of Pond Effluents and Mud

Yang Yi and C. Kwei Lin
Aquaculture and Aquatic Resources Management
Asian Institute of Technology
Klong Luang, Pathumthani 12120, Thailand

A wide range of aquaculture systems is practiced in Asia, predominantly in semi-intensive systems with fertilization and intensive systems with formulated feeds in pond culture. This paper describes various means to minimize environmental impacts and reuse pond effluents and bottom mud, based on a series of pond experiments of the most commonly cultured species in Thailand, hybrid catfish (Clarias macrocephalus Clarias gariepinus) and Nile tilapia (Oreochromis niloticus). Experiment 1 was designed to improve feeding efficiency through optimization of feeding regime to reduce nutrient inputs in Nile tilapia culture; the results show that there were no significant differences in fish yield among daily feed rations at 50%, 75%, and 100% satiation, but the nutrient loading was escalated with increasing rations. The second experiment on hybrid catfish and Nile tilapia culture in cage-cum-pond systems shows that major nutrient input from formulated feed could be effectively recycled in a closed pond where hybrid catfish were cultured intensively with formulated feed in cages and Nile tilapia with natural food in an open pond. The third experiment was conducted to determine appropriate harvest methods and draining treatments for reducing pollutants from Nile tilapia ponds; the results show that liming pond water a day before draining and gradually draining ponds to a 25-cm depth during harvest was most effective. An experiment conducted to reuse effluents from hybrid catfish culture to fertilize rice crops demonstrated that the rice crop removed 32% total nitrogen (TN) and 24% total phosphorus (TP) from the effluents, with rice production comparable to that which received regular fertilization regime. The last experiment was to determine the efficiency of rooted aquatic plants in extracting nutrients from pond mud. The results show that the economic aquatic plants, such as lotus (Nelumbo nucifera), were able to remove 300 kg N and 43 kg P/ha/year from pond substrates.

This abstract is excerpted from the original paper, which was published in Aquaculture, 226:57 & 68.57R>
CRSP Research Report 03-197

A Comparative Analysis of the Fixed-Input,
Computer Modeling, and Algal Bioassay
Approaches for Identifying Pond Fertilization Requirements for Semi-Intensive Aquaculture

Chris Knud-Hansen and Hans Guttman
Aquaculture and Aquatic Resources Management
Asian Institute of Technology
Klong Luang, Pathumthani 12120, Thailand

Kevin Hopkins
Pacific Aquaculture and Coastal Resources Center
University of Hawaii at Hilo, Hilo, Hawaii 96720 USA

This paper compares three different strategies/treatments for determining fertilization rates for producing natural foods in semi-intensive aquaculture ponds. The first strategy used a predetermined, fixed-input rate of nitrogen (N) and phosphorus (P) based on results from previous yield trials. The second strategy was based on algal nutrient concentrations, and used biweekly water quality measurements in combination with a microcomputer-based expert system, PONDCLASS , to determine fertilization rates. The third approach, the algal bioassay fertilization strategy (ABFS), was based on algal growth responses to nutrient [i.e., N, P, and carbon (C)] enrichment, and used weekly, pond-specific algal bioassays to determine both nutrient requirements and associated rates of nutrient inputs. The three fertilization strategies were applied to Nile tilapia (Oreochromis niloticus) growout ponds over a 120-day period, with five ponds per treatment. All ponds were fertilized weekly with urea, triple superphosphate, agricultural lime, and/or chicken manure in amounts determined by each strategy.120>
Results indicated that net fish yields (NFYs) were not significantly different (P = 0.094) between treatments, with the fixed-input treatment giving the highest but most variable yields. Average NFYs S.E. (standard error) for the 120-day growout period were 2124 276, 1476 151, and 1651 133 kg ha-1 for the fixed-input strategy, PONDCLASS , and ABFS treatments, respectively. The relatively lower NFYs for PONDCLASS and ABFS indicate that neither approach maximized fish production.
Nitrogen utilization efficiencies of fertilizer inputs were similar for all three strategies. Although the fixed-input approach used approximately 20% more N than the other two approaches, mean algal productivities and NFYs were also proportionally higher with this treatment. This result is consistent with the observation that algal productivities in PONDCLASS
and ABFS ponds were nearly always limited by N availability.
However, both P utilization and fertilization cost efficiencies were significantly better with PONDCLASS
and ABFS than with the fixed-input treatment. The fixed-input approach not only used a higher P input rate than necessary, it did not account for ecological differences between ponds within
. . .continued on p. 9
image4.gif
Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12