Brno Reservoir (259 ha) is one of the most intensively utilised waterbodies in the Czech Republic, being used simultaneously for recreation, sport, fisheries, boating and electric power production. Despite this, no consistent fish survey has yet been performed at the reservoir. Between 2009 and 2012, a number of measures, including fish biomanipulation, were applied to improve water quality. Large cyprinids (mainly common bream Abramis brama) were removed and predatory fish (e.g. pike Esox lucius, zander Sander lucioperca) stocked. In September 2012 and 2013, we carried out an extensive study of the fish community in order to describe the present fish assemblage and evaluate the success of biomanipulation. Fish were sampled at 11 locations using electrofishing (inlet zone) and beach seining (lake zone). Twenty-three species and one hybrid were recorded (inlet zone – 20, lake zone – 14), with roach Rutilus rutilus and bleak Alburnus alburnus (plus perch Perca fluviatilis) dominant in inlet samples, but carp Cyprinus carpio dominant by biomass; and white bream Blicca bjoerkna and roach dominant in the lake zone, both by abundance and biomass. Predatory species represented 14-17 % of biomass in both the inlet and lake zones in both years. The final results of biomanipulation were questionable. While a low proportion of adult bream suggests successful removal, populations of small cyprinids, such as roach and white bream, increased in compensation. There was little evidence for an increase in predatory fish following stocking, probably due to angling pressure. Our results indicate that biomanipulation to improve ecological water quality in reservoirs is unlikely to be successful when they are managed specifically for carp and predator angling.
This report addresses the possible impacts of local habitat characteristics on the metacercariae of Clinostomum schizothoraxi Kaw, 1950 infecting crucian carp, Carassius carassius (Linnaeus), from three lakes in Kashmir. The lakes chosen encompass an extremely wide gradient in trophic status - Manasbal (less polluted and mesotrophic), Dal (moderately polluted and eutrophic) and Anchar (strongly polluted and hypertrophic). The results indicate that infrapopulation-level descriptors of abundance of C. schizothoraxi in fish differed between the three lakes and revealed that the infection levels were greater at Anchar Lake. Furthermore, the prevalence, mean abundance and mean intensity of infection also changed during the period of investigation along the seasonal gradient of water temperature. The fact that the abundance patterns of the parasite differed in different populations of the same host provided a unique opportunity for a comparative study on the temporal variations in infection patterns attained during different seasons. In particular, the lake environments showed a high degree of variability in the density profiles of mollusc intermediate hosts and, thus, the differences in the infection status of crucian carp were derived on the basis of intermediate host population size which, in turn, was influenced by the trophic characteristics of the three lakes.