Author(s): Parag Deka, MM Goswami

Abstract: The study is conducted on the productivity of lower trophic status in two types of pond environment in an aquaculture system located in the Aquaculture campus of Gauhati University, Assam. One type of experimental pond (Pond A) is manually managed having fertilization effect of inorganic and organic fertilizers while the other is a naturally managed pen culture pond (Pond B) surrounded by dense reed swamps. The lower trophic system is constituted by planktonic productivity in the fertilized pond seen to be influenced by application of lime and other fertilizers in one hand and in the other hand the pen culture pond got influenced by leasing nutrient from the swamps. The seasonal variations of both phytoplankton and zooplankton densities are compared in both the pond types to determine their fluctuation trend and productivity state. The seasonal variations of phytoplankton productivity in the studied ponds are not well marked, despite the soil of Pond B is nitrogen limiting. However, zooplankton productivity of the two ponds shows significant variation. Phytoplankton exhibits bimodal pattern of seasonal growth in Pond A while tetramodal in Pond B. The study also reveals that Chlorophyceae is the most dominant group in terms of population density over the other phytoplanktonic group. The next dominant group of phytoplankton is Myxophyceae with blooms of Microcystis aeruginosa during late monsoon to early autumn in Pond A indicating inclination toward eutrophic condition. Stastical analysis reveals a bimodal pattern of plankton production with a significant negative correlation between phytoplankton and zooplankton for both the ponds. The study also reveals that productivity of phytoplankton is found to be more than that of zooplankton productivity.

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