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PD/A CRSP Research Reports 93-51 to 93-55

PD/A CRSP Research Reports 93-51 to 93-55

Analyzing standard curves in the chemistry of waters used for aquaculture

Christopher F. Knud-Hansen, Agricultural & Food Engineering Division, Asian Institute of Technology, G.P.O. Box 2754, Bangkok, 10501, Thailand

30 April 1993, CRSP Research Report 93-51

Abstract The fundamental principle in colorimetric analyses of water chemistry is the relationship between concentration of a particular chemical and color intensity. Color intensity is determined by measuring the absorbance of light of a particular wavelength. The relationship should follow a standard curve made with a series of standard concentrations selected to cover the expected range of unknown samples. The absorbance of a solution is directly proportional to the concentration of absorbing constituents at a fixed light pathlength, and directly proportional to the pathlength at a fixed concentration. Within a certain range of concentrations, the relationship is linear (y = a+bx, where y = absorbance, a = the y-intercept, x = concentration and b = slope of line). Linear regression can be utilized to determine the slope (b) of the line and the regression coefficient (r), which describes how well the straight line fits the plotted points from standards. Some spectrophotometers measure only transmittance, in which case the logarithm of transmittance should give a linear relationship with concentration. As reliable standard curves are essential, the purpose of this article is to help aquaculture researchers identify, troubleshoot, and hopefully correct common problems associated with colorimetric analysis of water.

This abstract was excerpted from the original paper, which was published in NAGA, International Center for Living Aquatic Resources Management, Manila, Philippines, 1992.

Diel cycles of planktonic respiration rates in briefly incubated water samples from a fertile earthen pond.

James P. Szyper and Joel Z. Rosenfeld
Hawaii Institute of Marine Biology School of Ocean and Earth Science and Technology, University of Hawaii, Kaneohe, Hawaii 96744

Raul H. Piedrahita and Philip Giovannini, Department of Agricultural Engineering, University of California at Davis, Davis, California 95616

30 April 1993, CRSP Research Report 93-52

Abstract Planktonic community respiration rates were assessed every 30 min through two 48-h periods in near-surface water taken automatically from a fertilized earthen pond and incubated in a plastic chamber for 21 min of each sampling cycle. Parallel records of water temperature, air temperature, windspeed, and solar irradiance permitted calculation of gross and net primary production and photosynthesis-irradiance relationships. Nighttime respiration rates generally matched oxygen depletion rates in pond water, indicating that incubation-based rates were representative of a quickly darkened pond community throughout the day. Daytime rates averaged nearly 2 times the mean night rate and 58% higher than the mean day rate determined by a typical interpolation used in free-water production calculations. Daily gross production ranged from 0.7 to 1.2 mmol O2 liter-1 d-1; respiration constituted 65-75% of gross rates. Gross oxygen production per unit Chl a during sampling intervals was light saturated at irradiance values > 600 µEinst m-2 s-1, with an asymptotic value of 1.58 umol O2 (µg Chl a)-1 h-1. This system and method were capable of resolving respiration and gross and net production when chlorophyll concentrations were near 40 µg liter -1.

This abstract was excerpted from the original paper, which was published in Limnology and Oceanography, 37(1992), 1193-1201.

Integration of intensive and semi-intensive aquaculture concept and example *

C. Kwei Lin, Agricultural and Food Engineering Division, Asian Institute of Technology, GPO Box 2754, Bangkok, Thailand

Kitjar Jaijen, National Inland Fisheries Institute Bangkhen, Bangkok, Thailand

Vorathep Muthwan, Marine Biology Department, Srinakarinvirot University, Chonburi, Thailand

May 21, 1993 CRSP Research Reports 93-54

AbstractAn experiment on integrated walking catfish-tilapia culture was conducted for 5 months. The walking catfish were stocked at 400 and 800 fish/cage in two 4-m3 nylon cages, which were suspended in each of two 250-m2 earthen ponds. Sex-reversed male tilapia (Oreochromis niloticus) were reared at 1 fish/m2 in the open pond. Whereas the catfish were reared with supplemental feed, tilapia were solely dependent on the natural diet derived from the recycled catfish waste. Weekly analysis of temperature, dissolved oxygen, ammonia, total phosphorus, total Kjeldahl organic nitrogen and chlorophyll a in the pond water showed that water quality was suitable for both tilapia and catfish growth. Total catfish and tilapia production was approximately 100 and 140 kg/pond, respectively. The experiment demonstrated that tilapia can efficiently use catfish waste and maintain desirable water quality.

This abstract was excerpted from the original which was published as CRSP Research Report 93-54 by the Program Management Office of the Pond Dynamics/Aquaculture Collaborative Research Support Program (PD/A CRSP).

* The full version of this report is available as a 342 K Acrobat file. It can also be ordered in hard copy format.

Photosynthesis and community respiration at three depths during a period of stable phytoplankton stock in a eutrophic brackish water culture pond.

James P. Szyper* and James M. Ebeling, *Hawaii Institute of Marine Biology, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, PO Box 1346, Kaneohe, Hawaii 96744 USA

September 15, 1993, CRSP Research Report 93-55

Abstract A 14 d period of dense but stable phytoplankton stock in a brackish water earthen pond (0.2 ha area, 0.7 m depth) was characterized to provide a baseline for study of instability. Results illustrate the potential of ponds to serve as microcosms of natural systems. Primary production and community respiration were assessed by diel curve analysis of oxygen and inorganic carbon sampled every 30 min at 3 depths. Neither stocks nor diel oxygen regimes were destabilized by 2 isolated days of low light, the first accompanied by heavy rainfall. Among nutrient elements, only inorganic nitrogen exhibited marginally limiting values. Daytime net production (dNPP) of oxygen ranged from 0 to 0.26 mol m-2 d-1, carbon uptake from 0.01 to 0.22 mol m-2 d-1. Nighttime respiration (nR) approximately matched dNPP, resulting in low mean diel net production (NPP). Minimal estimates of daytime respiration (dR) were substantially greater than nR and dNPP; minimal gross production (GPP = dR + dNPP) averaged 2.5 times dNPP. Estimated dR varied with dNPP in a stabilizing negative feedback, possibly mediated by photosynthetic products. Both dNPP and NPP varied with diel irradiance, but nR did not. Both dNPP and nR decreased with depth; positive NPP was concentrated in the upper layer. Stocks and oxygen cycles were more resistant to disturbance by low light than predicted by models assuming 1.0 m pond depth. We suggest for further examination that stability was related to the shallow depth of this pond, which permitted sufficient light penetration to the bottom layer for positive dNPP on most dates.

This abstract was excerpted from the original paper, which was published in Marine Ecology Progress Series 94:229-238, 1993.

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