Study on the Changes of Biotic Variables, Their Influence on the Primary Productivity and the Effect of Manuring of Fish Ponds

The experiment was carried out in the period 2004-2006 on seven fish ponds of the Institute for Fishery and Aquaculture in Plovdiv city, Bulgaria with a single area varying from 1.8 to 3.9 daа. Powered fertilization with cattle manure on dose 3000 kg.ha-1 was applied. The aim of the experiment was to study the relations between the biotic factors (zooplankton, phytoplankton, zoobenthos, chlorophyll a, macrophytes, bacterioplankton, percent of energy utilization by primary productivity (PEU), their influence on the primary productivity and the effect of manuring on the fish ponds. The bigger part of the biotic factor variation was defined by the differences between the monthly samplings compared to the changes between the ponds within the period of investigation (2004/05/06). There was a difference between the first and last months concerning the biotic factors. This great seasonal variability decreases the opportunity for revealing the differences between the manured and the control ponds. The biotic factors as the PP (primary productivity), respiration and PEU in the manured ponds were higher compared to the control ponds during 2005. More macrophytes and higher PP/respiration and PP/chlorophyll а ratios were detected in the control ponds. Increased biotic variable values of the PP, respiration and chlorophyll а were found in the manured ponds during 2006. The derived relationships might contribute for enhanced productivity of carp ponds and for improvement of existing management practices in the view of better water quality in fish farming.