Feeding behaviour of two functional groups of 0+ perch Perca fluviatilis (epilimnetic, staying all 24 hours in epilimnion; hypolimnetic, daily migrating between hypolimnion and epilimnion) were investigated in the deep canyon-shaped Slapy Reservoir (Czech Republic) during two 24-h periods in late May and mid June 2002. Densities of most favoured cladocerans and copepods were generally higher in epilimnetic than in hypolimnetic zones. The two 0+ perch groups fed predominantly on cyclopoid copepods during the daytime in May. In June, epilimnetic perch fed on cladocerans (Daphnia sp., Diaphanosoma brachyurum), whereas hypolimnetic perch preferred calanoid copepod Eudiaptomus gracilis. Throughout darkness, when nearly all perch occupied upper strata, their gut contents were clearly dominated by cladocerans Daphnia sp. and Diaphanosoma brachyurum in May and June, respectively. Digestive tract fullness (DTF) of hypolimnetic perch was 2.0–2.8-times lower than the DTF of epilimnetic perch, and a higher share of perch with empty digestive tracts was found in the hypolimnion. Maximum DTF occurred in the epilimnion during the day and/or dusk, whereas at night and dawn progressive evacuation of guts was recorded and migrants returned with low DTF back to the hypolimnion. Low zooplankton abundance, unfavourable light and temperature conditions in the hypolimnetic zone are suboptimal both for prey searching and for overall metabolic processes.
Ligula intestinalis (Linnaeus, 1758) is a tapeworm parasite with a worldwide distribution that uses a wide variety of fish species as its second intermediate host. In the present study, we investigated the prevalence and population genetic structure of plerocercoids of L. intestinalis in five common cyprinoid species, roach Rutilus rutilus (Linnaeus), freshwater bream Abramis brama (Linnaeus), white bream Blicca bjoerkna (Linnaeus), bleak Alburnus alburnus (Linnaeus), and rudd Scardinius erythrophthalmus (Linnaeus), collected in six water bodies of the Czech Republic (Milada, Most, Medard, Jordán, Římov and Lipno). Of the six study sites, the highest frequency of parasitism was recorded in Lake Medard (15%). The overall prevalence rate among the species was as follows: roach > rudd ≥ freshwater bream > bleak > white bream. Two mitochondrial genes (cytb and COI) were used to compare the population genetic structure of parasite populations using selected samples from the five fish species. The results of the phylogenetic analysis indicated that all populations of L. intestinalis were placed in Clade A, previously identified as the most common in Europe. At a finer scale, haplotype network and PCoA analyses indicated the possible emergence of host specificity of several mtDNA haplotypes to the freshwater bream. Moreover, pairwise Fixation indices (FST) revealed a significant genetic structure between the parasite population in freshwater bream and other host species. Parasite populations in roach not only showed the highest rate of prevalence but also depicted a maximum number of shared haplotypes with populations from bleak and rudd. Our results suggest that recent ecological differentiation might have influenced tapeworm populations at a fine evolutionary scale. Thus, the differences in prevalence between fish host species in different lakes might be influenced not only by the parasite's ecology, but also by its genetic diversity.
Diel feeding patterns of subadult and adult cyprinids of three species (roach Rutilus rutilus, bream Abramis brama, bleak Alburnus alburnus), which foraged almost exclusively on microcrustacean plankton, were studied in the meso-eutrophic Římov Reservoir (Czech Republic). All cyprinids showed a daytime feeding periodicity, with a marked night-time decline in gut fullness. Diel variations in gut fullness were observed in roach 200–270 mm standard length (SL) and bream 220–330 mm SL during May and in bleak, roach and bream of 110–170 mm SL, respectively, during August. Our results corroborate other studies in which light intensity has been found to be an important factor affecting cyprinid foraging on zooplankton. Daily zooplankton consumption rates ranged from 1.5 % of wet body weight in bream (220–330 mm SL) to 9.9 % of wet body weight in bleak (110–170 mm SL).
In the deep and slightly eutrophic dam part of the Římov Reservoir (Czech Republic), the fish use of open water habitat was studied by means of gillnetting, hydroacoustics and diet analyses during the period from April to October 2005. The day and night acoustic surveys revealed majority of pelagic fish present in the upper 5 m of the water column. The highest gillnet catches of planktivorous fish in epipelagic waters were obtained in May and August. The lowest fish catches were recorded in April and October which resulted in significant positive correlation between the gillnet catch per unit effort and water temperature. The majority of captured fish were adults of three cyprinid species: roach Rutilus rutilus, bleak Alburnus alburnus and bream Abramis brama. In the early spring the food of the three species was diversified: bream consumed primarily cyclopoid copepods, bleak fed on terrestrial insects, and gut content of pelagic roach consisted mainly of littoral food components, algae and detritus. In the late spring and summer however, the diets of all three cyprinids were predominated by large cladocerans, thus proving the use of open water habitat abundant in this prey.