The effect of dietary immunostimulants on the susceptibility of common carp (Cyprinus carpio) to the white spot parasite, Ichthyophthirius multifiliis.

One of the main obstacles in freshwater aquaculture is the parasitic ciliate Ichthyophthirius multifiliis (Ich), the causative agent of white spot disease. The use of immunostimulants as feed additives may be a promising approach to control Ich infection. In the present study, we tested the prophylactic effect of orally administered ß-1,3/1,6-glucan and propolis extract E50 against Ich infection in common carp. In total, 122 fish were separated into three experimental groups fed with a control, 3% ß-glucan and 1% propolis diet for 40 consecutive days, respectively. On day 40, 16 fish per group were individually exposed to Ich theronts and the number of trophonts was counted 5 days post exposure. Relative gene expression of interleukin 1-ß (IL-1-ß) in common carp liver was examined by qPCR. Compared to control, the mean infection intensity was lower in the ß-glucan- and propolis-fed groups; however, the difference was not statistically significant. The relative expression of IL-1-ß significantly decreased in the propolis-fed group at day 10. In the ß-glucan-fed group, a significant IL-1-ß decrease was detected at day 15 compared to control. Although the Ich infection intensity was slightly decreased in both treated groups, and IL-1-ß was moderately down-regulated in the liver of common carp, our results suggest that the applied feeding regime is insufficient to prevent Ich outbreaks in common carp.

Selection of the host's habitat by cercariae: from laboratory experiments to the field.

The distribution of cercariae was studied in 18-cm-sized cuvettes under different lighting conditions, in Plexiglas cylinders (80 cm high) vertically placed in a pond, and when swimming freely in a pond. The vertical distribution and the effect of light intensity on it were relatively similar in the cuvettes, in the cylinders, and in the pond. Each of the species (Schistosoma mansoni, Diplostomum spathaceum, Echinostoma caproni, and Pseudechinoparyphium echinatum) showed its individual distribution within the water column, with distinct changes during the time after shedding. We hypothesize that the species-specific distributions in the water reflect behavioral adaptations to increase the chances of encountering the host spectra.