Functional alterations associated with "winter syndrome" in gilthead sea bream (Sparus aurata)

Gilthead sea bream obtained from a fish farm in the Delta de l'Ebre (Tarragona, Spain) were used to study various functional alterations associated with "winter syndrome." The fish groups considered were: control fish routinely sampled 3 weeks before an outbreak (which took place in March 1998); winter syndrome symptomatic fish (assessed by eye and corroborated through histopathological analysis); and asymptomatic animals sampled from the same tank where winter syndrome fish were found. Winter syndrome animals weighed less than control and asymptomatic fish. The symptomatic animals suffered a drop in the haematocrit and number of erythrocytes, although red cell volume did not change. Furthermore, the concentration of total plasma proteins in winter syndrome fish was higher than in control animals, due to a rise in β₂- and γ-globulins; the α₂-globulin concentration was lower and albumin and α₁- and β₁-globulins remained unchanged. A significant increase in the concentration of plasma amino acids, both essential and nonessential, was found in symptomatic fish. This group of animals showed a lower plasma glucose concentration. There were no differences in either the plasma sodium or chloride concentrations between control and symptomatic fish. Instead, the plasma potassium concentration in winter syndrome animals doubled that of control animals. The plasma concentrations of calcium and magnesium were lower in symptomatic animals than in control fish. Symptomatic fish showed high lipid concentration in liver and elevated plasmatic GOT activity, indicating hepatic damage. No other significant differences in the composition of liver and white muscle were found between control and symptomatic animals.