Theses and Dissertations

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Defense Date

1999

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Second Degree Name

M.S. Coastal Zone Management

Department

Oceanographic Center

First Advisor

Bart Baca

Second Advisor

Curtis Burney

Third Advisor

Richard Spieler

Abstract

A wastewater treatment plant was converted for use as an aquaculture research facility. To compare the growth of hybrid tilapia in shallow and deep tanks, thirty sex-reversed hybrids of Oreochromis niloticus x Oreochromis aureus were stocked in three shallow tanks (1.47 m in

diameter x 0.65 m in depth) and their growth was compared to 7,000 hybrids stocked in deep (8.5 m x 8.5 m x 4.0 m) tanks. Stocking density (1 fish/38L) was the same for all tanks. Winter growth in the small tanks ranged from 1.05 - 1.11 g/day compared to 0.802 - 0.844 g/day in the deep tanks. ANOVA's and Student-Newman-Keuls tests showed that the growth of the hybrids within the shallow tank replicates and deep tank replicates was not significantly different but there were significant differences between shallow arid deep tanks. When the temperature rapidly decreased to a low of 13°C and remained between15°C and 25°C during a winter cold snap, the rate of growth in all of the tanks decreased to 0.0 g/day. After three months, the fish were sorted into100 g groups and placed in separate shallow and deep tanks. The different sizes still grew at significantly different rates in the shallow and deep tanks. The low temperatures continued to be a major factor affecting growth, particular1y with the < 100g fish in the deep tanks, which did not grow for 2 months. Over feeding of the hybrids became difficult to avoid because of rapid changes in feeding behavior in the deep tanks due to temperature fluctuations. Consequently, the concentration of dissolved oxygen decreased and ammonia levels increased. The results of this study showed that fish growth in large, deep tanks lagged slightly behind that of more easily managed, small, shallow tanks, and that periods of cold weather result in cessation of growth. However, the study also showed that fish culture is possible in large tanks common to wastewater treatment facilities. Although the winter culture of tilapia was successful in these tanks, heating during colder periods would be required to maintain adequate growth rates.

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