A thesis submitted in partial fulfilment of the requirements for the degree of master of science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1989

An experiment was conducted for a period of 4 months to compare the production of tilapia <Oreochromis niloticus) cultured in open pond, cage and pen in 3 semi-intensive ponds. Chicken manure were applied to the ponds at the rate of 250 kg chicken manure (dry weight> I hectare/week and urea was added to make up the desired N:P ratio of 5:1 throughout this experiment. Fish production, growth and nutritional values of pond inputs, pond water quality, detritus quality and organisms were determined during the experiment. The mean daily fish weight gain in pond, cage and pen were 0 .94, 0.93 and 0.97 g/fish/day with mean survival of 90.5%, 93.9% and 90.3%, respectively. The extrapolated total net yield of Nile tilapia was 5586 kg/ha/yr in the pond, 5307 kg/ha/yr in the cage and 5953 kg/ha/yr in the pen. However, t here was no significant difference for fish production and survival rate in those 3 treatments. Analysis of fish stomach contents showed that similar fish diet was found in three cultural systems. They consumed mainly phytoplankton, of which the dominant species were Microcystis sp and Anabaena sp. The ranges of pond water quality were as follows: total ammonia 0 .38 ±0.10- 1.61 ±0 .15 mg/l; temperature 28.1-31.4 °C ; pH value 8.10-9.12 ; dissolved oxygen from dawn to sunset 2. 1 ±0.4-8.6 ±0.5 mg/l. The phytoplankton biomass in three ponds increased with time and the highest biomass was 19.10 ±7.02 mg/l (dry wt). · The mean detrital deposition to pond bottom estimated for dry matter and organic matter were 333.5 ±11 3.4 g/ m2 /day and 292.72 ±105.33 g/m2 /day, respectively. The mean deposition of chlorophyll-a in detritus was 52 ±4.5 mg/m2 /day.