Effects of photoperiod on growth performance, body composition and antioxidant capacity of fat greenling juvenile Hexagrammos otakii.

Abstract

As one of the major environmental factors, photoperiod plays an important role in factory aquaculture systems, and the effects of photoperiod on organism performance appear to be species specific. To determine a suitable light photoperiod that optimizes production efficiency, the effects of three commonly used photoperiods 12L (12 h light):12D (12 h dark), 24L and 24D on body composition and antioxidant capacity of juvenile fat greenling Hexagrammos otakii were assessed. The initial weight of the fish in this feeding test was 11.07 ± 0.16 g, and the trial lasted for 30 days. The effects of these three photoperiods on growth performance were also tested. Juvenile fat greenling reared under 24D shows significant growth performance, with significantly higher feed efficiency and significantly lower feed rate. However, there was no significant difference in growth performance between the other two treatments. On the 10th day of the experiment, the hepatic antioxidant enzyme activities in 24L and 12L:12D treatments were all significantly greater than those in 24D treatment. However, at end of the culture trial, hepatic antioxidative enzyme activity was suppressed, and the highest malondialdehyde concentration was observed at 12L:12D, followed by 24L and then by 24D, implying relatively greater degree of oxidative damage to lipids and proteins in 12L:12D and 24L groups. The photoperiod affected the muscle fatty acid (FA) level, and the level of FA was significantly higher in the 24D group than in the other two groups. The levels of saturated fatty acids (especially C24:0) and monounsaturated fatty acids (especially C18:1n-9) were significantly lower in the 12L:12D and 24L groups. The effect of photoperiods on the total muscle protein content of fat greenling juveniles was limited. Nevertheless, an obvious effect on amino acid composition, especially essential amino acid (EAA) composition, was observed, and the EAAs in the muscle of juveniles were sharply consumed to physiologically adapt to environmental variations in the 12L:12D and 24L treatments. These findings suggest that constant darkness promotes better growth, body composition and antioxidant capacity in fat greenling juveniles and that a changing photoperiod (light-dark conversion) may cause more stress in this reef-dependent species.