Development and physiological effects of viral erythrocytic infection (VEI) in naturally-infected cultured sea bass

Abstract

The development of viral erythrocytic infection (VEI) in naturally infected populations of sea bass ( Dicentrarchus labrax) cultured on the Mediterranean coast was studied. Infection could be detected in 2-month-old fish, and both the prevalence and level of infection increased progressively during the first year of life. In adult fish, the disease occurred as a chronic infection, with a significant decrease in the level of infection at temperatures over 20°C, and a seasonal pattern with high infection levels in winter and spring and low infection levels in summer and autumn. A decline in specific growth rate was observed associated with increases in the infection level. Various haematological parameters were differently affected in juvenile and adult populations of sea bass. The former presented a polycythemia pattern with increased red blood cell counts and haemoglobin concentrations associated with an increase in infection level. In the adult population, a moderate microcytic anaemia with decreases in mean corpuscular volume and mean corpuscular haemoglobin of red blood cells was observed in association with the increase in infection level.