Theses and Dissertations


Title: Evaluation of productivities of ponds treated with nitrogenous and non-nitrogenous fertilizer and different rates of stocking of Tilapia mossambica Peters, with reference to food habits and rates of growth

Name: Potaros, Manu

Degree: MS

Chair: Dr. John S. Dendy

Resides: FAA Library

University: Auburn

Location: Auburn, Alabama

Date: 1965

Pages: 41

Keywords: Pond Productivity,Nitrogenous Fertilizer,Non-Nitrogenous Fertilizer,Stocking Rates,Tilapia mossambica,Food Habits,Growth Rates.

Abstract:

From July 6 to October 14, 1964, an investigation was conducted in twelve 0.25-acre ponds that had been fertilized with complete inorganic fertilizer (N-P-K) from 1942 to 1959. Beginning in 1959 three fertilizer treatments (0-0-0, 0-8-2, and 8-8-2 of N-P-K) were applied with four replications of each treatment. The purpose of this investigation was to evaluate the effects of elimination of nitrogen from fertilization and the effects of various rates of stocking of fish upon the production, growth rate, and reproduction of Tilapia mossambica Peters. The ponds were stocked with 2,000, 4,000, 6,000, and 8,000 fish per acre in each fertilizer treatment. The ponds that received the 0-8-2 and the ponds that received the 8-8-2 fertilization produced greater weights of fish per acre than did the ponds that were not fertilized, but the 8-8-2 fertilization did not give greater weights of fish than did the 0-8-2 fertilization. Relative growth rate declined with increase in rate of stocking. The food habits of tilapia were studied by the "frequency of occurrence method". The digestibility of food-stuffs was studied by comparing the condition of food-stuffs from the anterior part of the gut with the food-stuffs from the posterior part. The viability of food organisms was studied by fecal cultures. The results indicated that tilapia fed mainly on phytoplankton and detritus. The zooplankton served as additional food, while benthic organisms were used as occasional food. Phytoplankton did not survive passage through the gut of the fish, but the eggs or adult form of ostracods remained alive as they went through the gut of tilapia. Other groups of crustacean zooplankton and benthic insect organisms were highly digestible. The rates of stocking influenced the weights of fish produced in fertilized ponds, but not in unfertilized ponds. From this investigation, the conclusion was reached that in ponds that had received complete fertilizer (N-P-K) for a long time, or in ponds in which there was sufficient natural nitrogen, the elimination of nitrogenous fertilizer will decrease cost of fertilizer but will not decrease the production of fish.

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