DEVELOPMENT AND PHYSIOLOGICAL-EFFECTS OF VIRAL ERYTHROCYTIC INFECTION(VEI) IN NATURALLY-INFECTED CULTURED SEA BASS

The development of viral erythrocytic infection (VEI) in naturally inf ected populations of sea bass (Dicentrarchus labrax) cultured on the M editerranean coast was studied. Infection could be detected in 2-month -old fish, and both the prevalence and level of infection increased pr ogressively during the first year of life. In adult fish, the disease occurred as a chronic infection, with a significant decrease in the le vel of infection at temperatures over 20-degrees-C, and a seasonal pat tern with high infection levels in winter and spring and low infection levels in summer and autumn. A decline in specific growth rate was ob served associated with increases in the infection level. Various haema tological parameters were differently affected in juvenile and adult p opulations of sea bass. The former presented a polycythemia pattern wi th increased red blood cell counts and haemoglobin concentrations asso ciated 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 a ssociation with the increase in infection level.