Masters Theses

Date of Award

6-1980

Degree Type

Thesis

Degree Name

Master of Science

Major

Wildlife and Fisheries Science

Major Professor

J. Larry Wilson

Abstract

The purpose of this study was to determine the feasibility of polyculturing channel catfish (Ictalurus punctatus) and tilapia (Tilapia aurea) in a high-density, flow-through culture system. Three densities of tilapia (3.0, 6.0, and 12.0 g/1) were polycultured with a common density of catfish (12.0 g/1). A monoculture treatment of catfish (12.0 g/1) was used for comparison. The effects of tilapia densities on catfish growth and condition were determined.

The fish were stocked in tanks containing 180 liters of water and having a flow rate of 2.0 1/min. Fish were individually weighed and measured at stocking and on day 90 at study's end. Gross weights of catfish and tilapia were taken for each tank every 14 days. Water quality parameters monitored were pH, temperature, dissolved oxygen, ammonia, and nitrate-nitrites. All data was analyzed using computer programs for nested analysis of variance and Duncan's multiple range test.

The growth and condition of channel catfish was significantly reduced in all polyculture treatments as compared to the catfish monoculture treatment. The mean weight gain after 90 days for monocultured catfish was approximately 49%, The best polyculture catfish growth was approximately 2% and occurred with 3 g/1 of tilapia. Growth and condition of tilapia was reduced only at the highest stocking density. Decreased catfish growth in the polyculture treatments was the result of competition for food. As the density of tilapia was increased, the competition for food was increased.

Water quality parameters other than dissolved oxygen concentrations were not significantly different between the treatments. Dissolved oxygen concentrations were significantly lower in the polyculture treatments, at times reaching levels which might have suppressed growth. Ammonia and nitrate-nitrite concentrations were low over the duration of the experiment and should not have affected growth.

It was concluded that polyculture of catfish and tilapia in a flow-through system is not practical for the densities studied. The significant decrease in growth and condition of the catfish in polyculture resulted in fish which were not marketable. Therefore it is recommended that commercial fish farmers not use the method described.

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