Optimization of fertilization rate for maximizing periphyton production onartificial substrates and the implications for periphyton-based aquaculture

The effects of four rates of application of fertilizer, with cow manure (30 00 kg ha(-1)), urea (100 (kg ha-1) and triple super phosphate (TSP) (100 kg ha(-1)) (treatment F)), treatment F x 0.5 (treatment 0.5F), treatment F x 1.5 (treatment 1.5F) and treatment F x 2 (treatment 2F), on periphyton, pla nkton and water quality in tropical freshwater ponds were studied. The high est periphyton biomass in terms of dry matter (3.27 mg cm(-2) substrate), a sh-free dry matter (2.06 mg cm(-2) substrate) and chlorophyll a (7.49 mug c m(-1) substrate) developed in treatment 1.5F. The ash content of periphyton was lower in treatment 1.5F (38% of dry matter) than in other treatments ( 57-66% of dry matter), Total ammonia and chlorophyll a of water increased w ith fertilization rate. Treatment 1.5F (cow manure, urea and TSP at rates o f 4500, 150 and 150 kg ha(-1) respectively) appears to be the optimum, yiel ding high quantity and quality periphyton. By supplying a substrate area fo r periphyton equivalent to the pond surface, it was estimated that this lev el of fertilization could support a fish production of around 5000 kg ha(-1 ) y(-1), without recourse to supplementary food.