EFFECT OF NUTRIENT MANAGEMENT ON PLANKTON COMMUNITY IN POND ENVIRONMENT

Abstract

Effect of nutrient management on the plankton community in pond was studied for three months in Sylhet Agricultural University campus, Sylhet. Twelve ponds were selected for four treatments with three replications; T0 was control treatment without any feed and fertilizer, T1 was treated with only fertilizer (cowdung-370.5 kg, urea 9.88 kg, TSP 9.88 kg per hectare), T2 was treated with fertilizer and feed (cowdung-370.5 kg, urea 9.88 kg, TSP 9.88 kg per hectare and half feed -twice daily) and T3 was treated with only feed (twice daily). Tilapia (Oreochromis niloticus) fry was stocked in all treatments and fed initially at 50% of their body weight on T3. Then it was gradually reduced up to 5% of body weight at the end of the study. Feed application rate in treatment T2 was half the amount of feed given in the treatment T3; fertilization was done weekly in treatment T1 and T2. Four groups of phytoplankton viz. Chlorophyceae, Cyanophyceae, Bacillariophyceae and Euglenophyceae and four groups of zooplankton viz. Rotifera, Copepoda, Cladocera and Crustacea were recorded in the present study. Chlorophyceae and Rotifera were found to be the most dominant groups of phytoplankton and zooplankton respectively. The mean abundance of both phytoplankton and zooplankton were found to show significant difference (P<0.05) among the treatments especially between T2 and T0. The recorded mean abundance (×10³ cells/l) of plankton was highest in treatment T2 (77) followed by T1 (55.71), T3

(41.76) and T0 (16.88). Fortnightly monitoring of selected physico-chemical parameters viz. temperature, pH, dissolved oxygen and transparency were carried out in all ponds and the recorded values were within the productive range. The study revealed that the control treatment (without feed and fertilizer) was not good for plankton on the contrary the application of both fertilizers and feed was better for the growth of plankton population in pond environment, which is ultimately beneficial for aquaculture. It may be recommended that application of fertilizer and supplemental feed is the best management technique of fish culture for fish farmer in general.