EFFECTS OF SOLAR ULTRAVIOLET RADIATION ON GROWTH, STRESS, PHYSIOLOGY AND INNATE IMMUNE FUNCTION OF GILTHEAD SEABREAM Sparus aurata REARED IN CAGES ON THE RED SEA COAST OF SAUDI ARABIA

Marine fish cage aquaculture industry in the Red Sea has been emerged as one of the priorities to respond to the increasing demand on seafood consumption by the Kingdom of Saudi Arabia population. The Red Sea, one of the most oligotrophic seas in the world, is characterized by clear waters and by receiving high levels of solar ultraviolet radiation. With the considerable penetration of ultraviolet B (UVB) across the water column, it is expected that the UVB radiation comprises an important threat to the fish, particularly those confined to the aquaculture cages as they could not avoid the UVB exposition. The aim of this study was to evaluate the sensitivity of the commonly aquaculture non-native species, gilthead seabream (Sparus aurata) to the Red Sea natural solar underwater UVB radiation levels.

Juveniles (32.03 ± 4.17 g) were exposed during 45 days to three different UVB experimental treatments representing the Red Sea natural UVB levels registered between 2 and 10 m depth in the water column: UVB2-5m (11.86 ± 1.79 kJ/m-2/d), UVB5-7m (6.06 ± 0.84 kJ/m-2/d) and UVB7-10m (2.40 ± 0.29 kJ/m-2/d). One experimental group without UVB exposure was used as control (CTRL). Growth and animal body condition, physiological condition, immune function and stress response of the fish were accessed after 1 day (single exposure), 10 days (short-term) and 45 days (long-term) of exposure.       

Seabream juveniles exposed to a single dose of UVB (UVB2-5 and UVB5-7) revealed a decline in the humoral innate immune parameters. After 10 days of exposure, fish from UVB2-5 and UVB5-7 treatments exhibited significantly lower body weight than those in the CTRL (Fig. 1). 13 % of mortality and severe skin sunburn lesions were observed in UVB2-5 after short-term exposure. Due to high mortality observed in UVB2-5, a human endpoint was done for this treatment after 16 days of exposure. After 45 days of exposure, lower body weight was observed in UVB5-7 and UVB7-10 when compared to the control (Fig.1). In addition, 8 % of mortality was observed in UVB5-7 and skin lesions were also evidenced in these fish. A decrease in the plasma total protein levels and antiprotease activity was observed after 45 days of UVB exposure. The present results indicate that the detrimental effects of UVB retarded fish growth, body condition, physiological status and reduced survival. In addition, the suppression of innate immune responses suggests that exposure to UVB has the potential to interfere and to increase the risk in S. aurata health in natural UVB doses present in the Red Sea waters.