Impact of amoeba and scuticociliatidia infections on the aquaculture European sea bass (Dicentrarchus labrax L.) in Portugal

Abstract

In this work, a survey of sea bass, Dicentrarchus labrax, for amoebae and scuticociliatidia infections was carried out to evaluate their effects on the aquaculture of this fish species. The study was conducted in two different fish farms, one using seawater and the other brackish water. Infection with parasitic amoebae was found to be fairly high (prevalence: 43-73%), being more frequent in sea bass from the brackish water system. Although it was never found to cause outbreaks of disease or mortality in the surveyed fish, amoebic gill disease (AGD) histopathological signs, i.e., hyperplasia, secondary lamellae fusion and cavity formation (interlamellar vesicles), were observed in fish manifesting no macroscopic lesions. Furthermore, some evidence was found that amoebae affects the fish's general state of health and growth rate. These results indicate that cautious and detailed surveys to detect this sort of infection, and thus carefully plan its control, are fully justified. Compared with amoebic infection, the prevalence of scuticociliatosis was found to be low (7-13%). No outbreaks of disease or mortality were ever recorded, even when scuticociliatidia was present in turbot raised in the same water system, leading to serious outbreaks of disease and mortalities in that species. This suggests that sea bass is far more resistant than turbot to such infections, and if this is the case, the former fish may be a good farming alternative when scuticociliatidia is present.