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Species composition and seasonal and spatial distribution of the crustacean zooplankton groups Cladocera and Copepoda were studied in two lake-type wetlands, the Mocskos-Danube and the Riha, and the Danube River at Mohács, located in the protected side of the Béda-Karapancsa National Park in the Middle Danube River, Hungary. The investigations were carried out from April to October in 2014. A total of 23 crustacean species were found, 17 Cladocera and six Copepoda. The species richness was the lowest in the river and the highest in the isolated Riha Lake. The total abundance, especially of some cladoceran species, was the highest in the connected Mocskos-Danube Lake in the spring during the high waters. Positive correlations of zooplankton with the organic carbon, temperature and total phosphorus were found. The correlation with chlorophyll-a was negative, indicating strong grazing pressure on the phytoplankton. The bacterioplankton, which had the highest abundance in the spring, during the flood in May, had a weak negative correlation with Copepoda and positive one with the attached bacteria, and with the alien species Eurytemora velox. Cladocera negatively affected only the medium-sized free-living bacteria. The macrophyte species Ceratophyllum demersum, better developed in Riha Lake, probably as a better competitor led to N- and P- limitations for the phytoplankton and bacterioplankton, and due to the isolation from the river these plankton communities had less development in Riha Lake compared to the Mocskos-Danube and Mohács sites. [ABSTRACT FROM AUTHOR]

Experiments measuring primary productivity, biotic and abiotic environmental factors in carp ponds were carried out within three consecutive years (2004, 2005 and 2006). The aim of the study was investigation of the relations between the biotic and abiotic variables, their influence on the primary productivity and the effect of manuring on the fish ponds. The influence of environmental factors onto primary productivity was investigated in ponds with and without organic manure. Nitrate nitrogen demonstrated the closest relationship with the gross primary productivity followed by chlorophyll a level and N/P ratio in manured ponds. When no manuring was applied, the importance of the nutrients along the food chain: nutrients- phytoplankton - zooplankton decreased. Trends, which can be used for increasing of productivity in carp ponds, were obtained. They give indications to improve the existing practices for better management of production efficiency and water quality in fish farms. [ABSTRACT FROM AUTHOR]

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 daa. 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 a ratios were detected in the control ponds. Increased biotic variable values of the PP, respiration and chlorophyll a 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. [ABSTRACT FROM AUTHOR]