Description

Abstract: The purpose of this study was to determine relations between physicochemical variables and primary productivity of fish yield using multiple regression analysis.

In Thailand, 8-12 pond (250 m2) were stocked with male Oreochromis niloticus (25-35 g) at a density of 1 fish/m3. Experiments were run for approximately 5 months during the wet season of 1984 and the wet and dry seasons of 1985. Ponds received nutrient inputs according to three different management schemes: (1) low input inorganic fertilizer (8 kg/ ha/month P2O5); (2) high input organic ferilizer (500 kg/ha/week chicken manure); and (3) high input inorganic fertilizer (100 kg/ha/week P2O5 and 30 kg/ha/week urea). Air and water temperature, solar radiation, rainfall, dissolved oxygen (DO), total phosphorus, nitrate-nitrite, ammonia, turbidity, chlorophyll a, primary productivity, fish weight, and fish survival were measured regularly throughout each experiment. Data were examined by regression analyses.

Ponds receiving high fertilizer inputs exhibited higher nutrient levels in water, higher primary productivity, and higher fish production than ponds treated with low inputs of fertilizer. Nitrogen and phosphorus appeared to be limiting factors for primary productivity, although multiple regression between these two factors and primary production indicated no significant relationship. The availability of nutrients may have been related more closely to regeneration rate than absolute concentration.

Fish yield was strongly correlated to rainfall, fish biomass, DO, water temperature and solar radiation. The correlation between net yield and fish biomass was a positive one, indicating that carrying capacity was not reached in the ponds.