Effects of illumination intensities on growth, digestive and metabolic enzyme activities and antioxidant capacities of juvenile Takifugu rubripes

Abstract

In this study, the impacts of various illumination intensities on growth, digestion and metabolism as well as antioxidant enzyme dynamics of Takifugu rubripes (0.03 ± 0.01 g) were investigated. Activities of alkaline phosphatase (AKP), acid phosphatase (ACP), pepsin (PPS), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) were measured. Juveniles were reared under four degrees of illumination intensities: 50 mW/m2, 250 mW/m2, 500 mW/m2 and 750 mW/m2, at a constant photoperiod (12D:12 L). Samples were collected at days 7, 14, 21, 28, and 35. After 35 days, the 750 mW/m2 light intensity was found to have significantly increased the final body weight, which was 1.1 ± 0.005 g. On day 35, PPS activities of T. rubripes juveniles in the 750 mW/m2 sample group were significantly low when compared to those of the 250 mW/m2 group while AKP activities in the 750 mW/m2 group were significantly higher than those of the 50 and 500 mW/m2 groups (p < 0.05). Low light intensity was unsuitable for the initial stages of T. rubripes. The 50 mW/m2 light intensity had a negative effect on weight gain of juveniles during the trial period. Moreover, at the end of the experiment, metabolic activities (ALT and LDH) in the 50 mW/m2 group were significantly low than those of other groups (p > 0.05). Even though they were relatively lower, there were no significant differences in SOD activities in the 250 mW/m2 group relative to the 500 and 750 mW/m2 groups. On day 35, high light intensity (750 mW/m2) resulted in stress responses that were characterized by T-AOC activities, and activity values were significantly lower than those of other groups (p < 0.05). These findings imply that different illumination intensities impact the early growth and physiology stages of T. rubripes, with the 250–500 mW/m2 light intensity being the most suitable.