| Description |
Seasonal variation of water characteristics, predominantly temperature, is considered to strongly affect fish physiology, including immune function. Then, the investment in many fish functions can vary in time due to the seasonal effects. Moreover, the parasite life cycle and the changes in their abundance are also influenced by seasonal changes through the water temperature. Therefore, we hypothesized that each potential host could be exposed to variety of parasite species which may negatively influence its viability, and for this reason host must generate enough effective immune system to increase a resistance against pathogens and reduce the fitness cost caused by parasitism. The aim of this study was to analyze the selected immunological and physiological parameters in common carp (Cyprinus carpio). Moreover, the seasonal changes in metazoan parasite infection were investigated and the possible associations between fish physiology, immunocompetence and parasitism were tested. A total of 120 individuals of common carp from farmed Vodňany population were studied during four different periods from 2007 to 2008 (i.e. early summer, late summer, autumn and winter). When comparing parasite abundance among seasons, Monogenea was the species richest and the most abundant group. The statistically highest values abundance were observed in early summer for Crustacea, in late summer for Cestoda, in autumn for Monogenea and Digenea. We also found the gender differences for total body length, body weight, gonad weight, gonado-somatic index (GSI), spleen-somatic index (SSI), erythrocyte count (RBC), hematocrit value (PCV) and haemoglobin level (Hb) and also for lymphocyte and monocyte counts. Significantly higher values of condition factor (CF), as well as the values connected with respiratory burst (RB) and phagocyte count (PH) were recorded in winter. Generally, the highest values of majority hematological parameters (RBC, PCV, Hb, MCV, MCH and MCHC) and SSI were recorded in early summer. The maximal values of lymphocyte and monocyte counts and lysozyme level were detected in late summer. In autumn, the statistically highest values of GSI and leukocyte count were found. By studying differential leukocyte counts, the remarkable changes were revealed in the composition of white blood cell components in different seasonal periods. Moreover, several associations between the parameters connected with physiological status, immunity and parasite abundance were found: the negative correlation between CF and the abundance of Monogenea, the negative correlation between SSI and both Monogenea and Cestoda, the positive correlation between SSI and both RB and PH. The results indicated the effect of the season on fish immunocompetence, parasitism and on the potential associations between these parameters.
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