Winter syndrome in the gilthead sea breamSparus aurata. Immunological and histopathological features

Gilthead sea breamSparus auratareared in the Mediterranean area are affected, during cold periods, by a pathological condition termed ‘ winter syndrome ’. This syndrome is causing significant losses in fish farms off the northeast coast of Spain. The histopathological study of affected fish revealed the presence of lesions in intestine, pancreas and white muscle. A survey of non-specific immune indicators (serum complement activity, erythrocyte agglutination, lysozyme activity, lymphocyte counts and oxygen radical production by macrophages) demonstrated a severe immunosuppression in fish samples in winter months, compared with those sampled during warmer periods of the year or after a period of recovery at higher temperature. No bacterial growth was detected from these fish. The observations are discussed in relation to water temperatures and to rearing conditions.