author(s)
Sampa Baidya and Arun Bhai Patel

abstract
Aquatic and free-floating water meal (Wolffia arrhiza L.) known for its fast reproduction rate was grown in differing restricted zones of supplementary feed based intensified carp polyculture in cement tanks (5m x 4m x 1m) with soil beds. While wolffia could not spread beyond the restricted zone, fishes could consume wolffia as per their desire by entering in the wolffia-zone from below. The main objective of the study was to evaluate the effects of area of wolffia-growing zone as% of total water surface area of the culture system on the overall water quality of the culture system Three levels of wolffia-zones viz. 10% (T₁), 20% (T₂), 30% (T₃) of the total surface area were evaluated against control without any wolffia (C). The culture period was 75 days and stocking density was 2 fish m^-2. The seeding rate of wolffia (0.5kg m^-2), feeding regime (constant feeding rate @2% d^-1 offered once a day) and fertilization rate involving cow dung, urea and single super phosphate were the same in all treatments throughout the study period. While no marked differences in the water quality parameters between treatments with wolffia-zone and control (without wolffia zone) were noticed in the early part of the experiment, the concentrations of NH₄-N (range 0.06-0.16 mgL^-1), NO₂-N (range 0.01-0.04 mgL^-1), NO₃-N (range 0.09-0.44 mgL^-1) and PO₄-P (range 0.01-0.02 mgL^-1) in the waters showed significantly lower values (P<0.05) for T₁-T₃ compared to those in control (C) with values of 0.23, 0.07, 0.75 and 0.02 mgL^-1, respectively. The overall mean concentrations of NH₄-N (0.21-0.42 mg L^-1), NO₂-N (0.06-0.11 mg L^-1), NO₃-N (0.23 -0.7mg L^-1) for the whole culture period were also significantly low in treatments with wolffia-zones. However, in general no marked differences were apparent among wolffia-zone treatments.