Effect of different levels of mineral phosphorus with and without nitrogen on the dry weight of planktonic biomass, increase in fish production and biomass conversion efficiencies.

摘要

An experiment to observe the effect of different levels of mineral phosphorus with and without nitrogen on the dry weight of planktonic biomass, increase in fish production and biomass conversion efficiencies was conducted at Fisheries Research Farms, University of Agriculture, Faisalabad in nine earthen ponds. The area under each pond was 30x16x2 m. Fingerlings of Hypophthalmichthys molitrix, Labeo rohita and Cyprinus carpio were collected from the Govt. Fish Seed Hatchery, Faisalabad and stocked in the experimental ponds with a stocking density of 251 each pond. The experimental pond 0 served as the control without any additives, whereas the pond 1, 2, 3, and 4 received mineral fertilizer (triple superphosphate, 46% P₂O₅) at the rate of 0.06, 0.09, 0.12 and 0.15 percent of wet fish body weight per day, while pond 5, 6, 7 and 8 received phosphorus in the same ascending order along with nitrogen (urea, 46%) at the constant rate of 0.12% N, of wet fish body weight daily and the study continued for twelve months. Fortnightly observations on an increase in fish production, dry weight of planktonic biomass and biomass conversion efficiency ratios were made. The overall range of increase in fish biomass in 24 fortnights under T₁, T₂, T₃, T₄, T₅, T₆, T₇, T₈ and T₀, were in the tune of 1.64-27.42, 1.65-20.93, 1.92-44.59, 1.46-43.70, 1.48-69.63, 2.65-32.24, 0.89-32.09, 1.45-41.46 and 0.59-3.31 g m-3; while the dry weight of planktonic biomass throughout the experimental period ranged from 43 to 176, 48 to 215, 42 to 220, 63 to 320, 49 to 327, 58 to 234, 48 to 210, 58 to 234 and 8 to 58 g m-3, respectively. The biomass conversion efficiency ratios ranged from 0.01 to 0.25, 0.02 to 0.24, 0.02 to 0.55, 0.01 to 0.26, 0.02 to 0.44, 0.02 to 0.30, 0.02 to 0.18, 0.01 to 0.32 and 0.02 to 0.25 in T₁, T₂, T₃, T₄, T₅, T₆, T₇, T₈ and T₀, respectively. Treatment pond, T₅ which was fertilized with 0.06 percent phosphorus plus 0.12 percent nitrogen remained the best treatment in which maximum net fish production of 462.51 kg pond-1 yr-1 was procured.