A condition in Sparus aurata larvae termed "distended gut syndrome" (DGS) has become a major problem in the past three seasons. Unable to digest rotifers and brine shrimp nauplii, the larvae develop a swollen abdomen, exhibit a disoriented spinning motion and are swept passively with the current. Bacterial or viral infections were suspected. Chloramphenicol-supplemented larval food did not affect the prevalence of DGS. Virus-like particles 80 nm in diameter were observed in necrotic cytoplasm of midgut wall cells.