A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science, School of Environment, Resources & Development

Thesis (M.Sc.) - Asian Institute of Technology, 1994

The effect of five stocking densities (5, 15, 25, 35 and 45/m3 ) and presence of tilapia ( Oreochromis niloticus) at each stocking density of Penaeus monodon on water quality, growth performance, nutrient retention and economic return were investigated and compared. The shrimps were grown in 5 m2 concrete tanks with a water volume of 3 m3 {u2022} Tilapia were grown in the cages (1.3 x 0.9 x 0.9 m) installed in shrimp tanks. Soil sediments were not present in the culture tanks and water was not exchanged. The experiment was conducted for 60 days. To the given amount of feed input, ammonia-N was negatively correlated to the stocking density. Irrespective of stocking density total inorganic nitrogen and chlorophyll-a increased linearly, and dissolved inorganic phosphorus increased exponentially with cumulative feed input. When tilapia was incorporated with shrimp culture, the ammonia-N produced to the given amount of feed input was lower and total inorganic nitrogen and chlorophyll-a were higher than system without tilapia. Nitrogen was the limiting nutrient in both culture systems and tilapia might enhance the chlorophyll-a production by regenerating the nitrogen from shrimp waste. Shrimp stocking density had a linear relationship with ammonia-N and total inorganic nitrogen concentrations, mulitplicative relationship with chlorophyll-a and no relationship with dissolved inorganic phosphorus. Dissolved inorganic phosphorus was correlated to the survival. In shrimps with tilapia system the chlorophyll-a was exponentially correlated to the stocking density. The high chlorophyll-a absorbed the nutrients and obscured any relationship with stocking density. Weight gain, survival and FCR were not correlated to the stocking density, but there has been decreasing trend towards increasing stocking density. Production was positively correlated to the stocking density. Nutrient retention by ·shrimp was unaffected by stocking density. There was a competition between tilapia and shrimps for natural food (detritus) which affected the weight gain, production and nutrient retention of shrimps. Tilapia is unlikely to be able to reduce phytoplankton biomass, but can be used to increase the production at lower stocking densities (5, 15 and 25/m3 ) of shrimps. In shrimp culture system without tilapia, stocking density can be increased unto 35/m3 without making any serious water quality problems with maximum economic returns.