RESUMO
Amyloodiniosis is a parasitological disease caused by one of the most common and important parasitic dinoflagellates in fish, Amyloodinium ocellatum (Brown), that represents a major bottleneck for gilthead seabream semi-intensive aquaculture in Southern Europe. In this experiment, we analyzed some metabolic, osmoregulatory and stress indicators to elucidate some of the physiological responses of gilthead sea bream when exposed to an A. ocellatum outbreak. We observed significant differences between Control and Infection groups in the cortisol, lactate and gill Na+/K+-ATPase (NKA) activity levels but that glucose, osmolarity, pH and total protein did not present such differences. This could indicate that the presence of the parasite induced a stress response, possibly enhancing the metabolization of glucose and subsequently lactate to cope with the higher energy requirements of the organism. There was also a decrease in gill NKA activity possibly due to severe epithelial damage and increased mucus production caused by the parasite A. ocellatum, which could induce anoxia and osmoregulatory impairment in the organism. However, further works must be performed to fully understand the physiological reactions of fish for A. ocellatum outbreaks.