Modification of stratified temperature model to accommodate reduced data inputs: identifying critical requirements

Steven D. Culberson and Raul H. Piedrahita, Department of Agricultural Engineering, University of California, Davis, California, USA

27 February 1995, CRSP Research Report 95-81

Abstract Accurate characterization of temperature stratification in ponds used for aquaculture is of critical importance in understanding how these ponds may be constructed, oriented, or otherwise managed biophysically when one wishes to provide optimal environmental conditions for the organisms cultured therein. While field studies can provide characterizations of water quality stratification at a single locale, to date there have been few attempts at developing reliable models which can be used at a variety of sites after initialization with appropriate local geographic and atmospheric data. In conjunction with Pond Dynamics/Aquaculture Collaborative Research Support Program (PD/A CRSP), the authors have modified a previously developed water quality model which closely predicts temperature stratification at several different sites in northern California. Changes in model structure and reduction of data requirements reflect the desire to provide for culturists the opportunity to predict stratification events with commonly available data, obtained either by hand or from a simple weather station located at or near the pond site. Validation of the model has been conducted with data sets generated through PD/A CRSP experiments, and the importance of wind vector and relative humidity inputs is considered here.

This abstract was excerpted from the original paper, which was presented at the Aquaculture `92 International Conference sponsored by WAS/AFS/NSA/ASAE . American Society of Agricultural Engineers paper No. AQUA-92-102, St.Joseph, MI, USA.

Development of production technologies for semi-intensive fishfarming during the past decade in central america

David Teichert-Coddington, Department of Fisheries and Allied Aquacultures, Alabama Experimental Station, Auburn University, USA

27 February 1995, CRSP Research Report 95-82

Abstract This paper reports on techniques that have been developed by the Pond Dynamics/Aquaculture Collaborative Research Program in Central America to increase Tilapia production by optimizing resource use in systems based predominately on natural pond productivity.

Tilapia yields in ponds fertilized only with phosphorus averaged 409 kg/ha and were unprofitable. Additions of 24 kg/ha nitrogen and enough phosphorus to maintain N:P ratios of 4:1 increased yields to 2079 kg/ha. Tilapia yield responded curvilinearly to chicken litter fertilization at weekly rates ranging from 125 to 1000 kg dry matter/ha; tilapia yields ranged from 1095 to 2593 kg/ha. Profitability was greatest at the highest litter application rate. Culture systems based solely on organic fertilization were nitrogen limited because of the low N:P ratio in chicken litter. Yields could be increased to 3600 kg/ha when weekly chicken litter applications at 750 kg/ha were supplemented with inorganic nitrogen to raise total available nitrogen to 25 kg/ha. Higher additions of nitrogen resulted in heavy blue-green algal blooms and decreased fish yields. Blue-green algae are thought to have out-competed other algae in the high pH and low CO₂ conditions that predominated during high nitrogen fertilization.

Weekly chicken litter inputs could be reduced to 500 kg/ha by substitution with equivalent inputs in inorganic N and P, but greater reductions resulted in lower primary production and fish yields. Primary production is believed to have been limited by CO₂ in ponds receiving low quantities of organic matter. Tilapia yields could be increased by use of prepared diets (20-25% protein), but profitability increased only when the Tilapia stocking rate was at least 2 fish/m², and feed was substituted with chicken litter for the first 2 to 3 months of a 5 month growing cycle. Ponds were stocked with male tilapia that had been either manually separated from mixed sex populations, or hormonally sex reversed. Neither technique of acquiring male Tilapia was 100% effective, so there was always reproduction in grow-out ponds. Reproduction could be practically eliminated, however if 500 Cichlasoma managuense (guapote tigre) fry or fingerlings were stocked per ha of pond. Efficient predation of reproduction was related to number of guapote stocked per area rather than per tilapia. Colossoma macropomun (tambaquí), a characid native to the Amazon and Orinoco River basins, was found to grow well with prepared diets, but performed poorly in ponds receiving only organic fertilization.

This abstract was excerpted from the original paper, which was presented at Actas del Simposia Investigación Acuicola en Centroamerica, p. 71-88.

Effects of protein diet and sowing density on the production of Penaeus vannamei in land tanks

David Teichert-Coddington, Department of Fisheries and Allied Aquacultures, Alabama Experimental Station, Auburn University, USA

27 February 1995, CRSP Research Report 95-83

Abstract A 2 x 2 factoral analysis was made to investigate the effect of protein diets on the growth of Penaeus vannamei sown at different densities in land tanks. The juvenile shrimp sown at densities of 4 x 8 shrimp/m² were fed 25% to 35% protein diets. The treatments were replicated from 3 to 4 times. At 99 days of growth there were no significant differences in terms of production, survival and average weight (P>0.05), between the two protein levels. The average production (kg/ha) for the 25% and 35% protein treated groups was 564 and 586, respectively, and the average weight (g) was 12.7 and 11.8, respectively. The shrimp production was significantly greater (P<0.05) when sown at a high density, while the average weight and survival in that case were significantly low. The average production at high and at low density was 624 and 533, respectively, and the average weight was 9.7 and 14.5 grams. The high density production, however, resulted in a reduced income because of the low unit price paid for small shrimp.

Note: The original paper is in Spanish.

This abstract was excerpted from the original paper, which was published in Revista Latinoamericana de Acuicultura. 35-29-44

Techniques for efficient and sustainable mass production of tilapia in Thailand

James P. Szyper, Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Hawaii, USA, and Aquaculture Field of Study, Asian Institute of Technology, Thailand

5 July 1995, CRSP Research Report 95-84

Abstract Tilapia culture in Southeast Asia is presently both spreading and intensifying. Researchers at the Asian Institute of Technology (AIT) have learned from and contributed to the sustainability of current techniques. Several hatcheries produce fry at rates exceeding two million fish per month using low-technology apparatus and methods developed at AIT. Fish survival and production rates in growout culture are enhanced by nursing fry to reasonable stocking sizes in hapa nets deployed in fertilized ponds, which may be fed relatively low quantities of inexpensive feeds, but produce reasonable yields with none at all. Inputs to growout ponds of on-farm organic materials (manures) and inorganic fertilizers can stimulate the ecosystems to be capable of supporting fish growth to more than 200 grams/fish without other feed inputs, with little disadvantage in growth rate compared to fed ponds, but with considerable economic and efficiency advantages. Beyond 200-300 grams/fish, growth is slower on plankton feeding alone because larger fish lack the capacity to acquire sufficient ration even in ponds with high plankton stocks. Feeding is begun as a supplement to plankton forage, and soon becomes the dominant nutritional source; rapid, near optimal growth is attained on a ration of approximately 50% of satiation amounts.

Economic analyses of these practices under current conditions in Thailand show reasonable viability despite some of Asia's lowest farm-gate tilapia prices and the incipient state of export enterprise in tilapia. The stability of the pond ecosystems during the growout periods without water addition to ponds indicates sustainable and efficient use of water resources in a region of seasonal drought. These practices offer hope of alleviating the predicted shortfalls in animal protein availability in rural areas of southeast Asia, and potentially workable scenarios for periurban enterprises serving, and using processing wastes and other inputs from, large urban Asian markets.

This abstract was excerpted from the original paper, which was published in Proceedings of the PACON International Sustainable Aquaculture 95 Symposium. Pacific Congress on Marine Science and Technology,1995, Honolulu, HI, USA. pp. 349-356.