Miloš Ćirić

Changes in the phytoplankton community and dominance of Cylindrospermopsis raciborskii (Wolosz.) Subba Raju in a temperate lowland river (Ponjavica, Serbia)

Species composition and seasonal succession of phytoplankton were analyzed in a lowland river located in South Banat (Ponjavica, Serbia). As a result of human activity, a network of irrigation channels was built on the Ponjavica River’s upper and lower courses. These channels reduce the water level in the river and help to create favorable conditions for accelerated eutrophication processes. Eight phytoplankton divisions with 444 taxa were present. Physical and chemical testing of water, phytoplankton abundance and biomass, as well as chlorophyll a concentration showed a high level of eutrophication. Cyanobacterial biomass developed in 2002 with dominance of Microcystis aeruginosa and Aphanizomenon flos-aquae. Changes in phytoplankton composition were observed during 2008, characterized by the appearance and dominance of Cylindrospermopsis raciborskii when this species accounted for more than 85% of the total phytoplankton biovolume. The change in dominant phytoplankton functional groups was observed: codons H1 and M characterizing summer in 2002 were replaced by codons SN and S1 in 2008. This study compares the presence of C. raciborskii with other phytoplankton species in relation to water quality parameters. High abundance of this species correlated positively with biochemical oxygen demand and turbidity, and negatively with NO3-N concentrations during the study period.

Driving factors affecting spatial and temporal variations in the structure of phytoplankton functional groups in a temperate reservoir

Abstract During the twenty-five years of existence, water quality has declined and severe blooms of cyanobacteria have occurred in the Grlište Reservoir. Changes in phytoplankton functional groups over time and along horizontal and vertical gradients were investigated in the course of a one-year study in this water-supply reservoir. We identified 19 dominant taxa, classified into 12 phytoplankton associations. The presence of the codons C, P, D and S1 differentiated the transitional from the lacustrine part of the reservoir. The nitrogen-fixing cyanobacteria Dolichospermum viguieri dominated the phytoplankton community in the epilimnion during August and September, when the reservoir showed P-limitation, but the bloom was not observed. The driving factors that accounted for the main variability in phytoplankton functional groups along the seasonal and vertical profile were identified using the direct gradient analysis (RDA). Our results revealed the importance of two bipolar factors. The first factor explained the variability in phytoplankton due to thermal stratification and physical mixing, each process affecting the algal community in contrasting ways. The second factor was interpreted as reduction vs. oxidation processes. Positive correlation between stratification and water pumping by a drinking water plant indicated that human activities were not severe enough to break down the thermal stability of the reservoir and to cause a cyanobacterial bloom.

Effect of supplemental feeds on liver and intestine of common carp (Cyprinus carpio) in semi-intensive rearing system: histological implications

Abstract In order to determine effects of different types of supplementary feed on the histology of liver and intestine of carp reared in a semi-intensive system, a six-month field experiment was carried out. Carp yearlings were fed different supplemental feeds: cereals (CF), pelleted (PF) and extruded (EF) compound feeds. Hepatocytes histomorphometry revealed larger nuclear profile area of EF-fed fish compared to other two groups, while cytoplasmic profile area of the hepatocytes decreased in following sequence: CF > EF > PF. Lower nucleus/cytoplasm ratio was found in CF-fed fish compared to EF-and PF-fed fish. Striking, season dependant finding, was that regardless of the type of supplementary feed the number of lipid droplets in hepatocytes was highest in July and August, lipid depletion occurred in September and October, while glycogen was present in hepatocytes throughout the study. No size difference between groups was observed for enterocytes height, absorptive surface height and number of goblet cells in tunica mucosa, but a strong relationship between length of intestinal folds and fish weight was found. Histological analysis revealed a difference among three types of supplemental feed used in this field study: extruded or steam-pelleted feed induced better nutritional status of common carp in comparison to cereals. At the same time, histomorphometry indicated some differences between EF-and PF-fed fish.