Outcomes of repeated exposure of the carp (Cyprinus carpio L.) to cyanobacteria extract

Abstract

The aim of this study was to examine the influence of a repeated exposure of the carp to the extract of cyanobacteria. We exposed carp embryos and larvae to the extract of cyanobacteria of the cumulative amount of microcystin LR, YR and RR of 1.3 μg·l-1 or 13 μg·l-1, respectively. One year later we exposed one half of these fish to the second dose of the extract of cyanobacteria of the cumulative amount of microcystins of 13 μg·l-1 and the second half to pure water to eliminate the influence of handling stress. The haematological and histological changes were examined. Similar changes of haematological indices were detected both after exposure to the extract and after the handling stress of fish. Especially indices of the red blood cells were characterised by significant increase (p ≤ 0.01 or p ≤ 0.05) of haematocrit value and haemoglobin concentration in groups with long-term exposure (30 days) during the early life stages as well as in control groups. The initial values of white blood cell count were significantly increased (p ≤ 0.01) in the control group and in the group exposed to the low concentration (1.3 μg·l-1) and after short exposure (8 days) during the early life stages as compare to other groups. The white blood cell count of these groups significantly decreased (p ≤ 0.01) after exposure to both pure water and the extract. Phagocytic activity was significantly decreased (p ≤ 0.01 or ≤ 0.05) after stress and after exposure to the extract in groups of long term exposure (30 days) during the early life stages in comparison to control and groups of low exposure. Total plasma protein concentration significantly increased (p < 0.01) in all groups after exposure to the extract in comparison to the initial values and only in groups of long term exposure during the early life stages and in the control group after the handling stress. The activities of aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) were decreased in groups of long term exposure during the early life stages after the exposure to the extract. Clinical and histological changes were not observed in any group of fish, except for the fatty infiltration of liver with a tendency to focal big droplet dystrophic steatosis in all groups of fish.