Photoperiods affect growth, food intake and physiological metabolism of juvenile European Sea Bass (Dicentrachus labrax L.)

Abstract Photoperiodism is a vital environmental factor that regulates the growth, development, metabolism, and reproduction of aquatic organisms. Here, we examined how different photoperiods (0L: 24D, 8L: 16D, 12L: 12D, 16L: 8D, 24L: 0D) with a full spectrum LED, influence growth, feeding, digestive enzymes, and antioxidant enzymes in juvenile European Sea Bass (Dicentrachus labrax L.). Specifically, a total of 300 fishes (body length: 13.5 ± 0.54 cm, bodyweight: 45 ± 5.3 g) were randomly divided into 5 different light treatment groups. Sampling and analysis were conducted after 60 days of the experiment. Results revealed significantly higher weight gain, specific growth rate, and daily growth index in the 8L: 16D group, relative to 0L: 24D and 24L: 0D. Conversely, feed conversion ratio (FCR) was significantly lower in 8L: 16D, 12L: 12D, and 16L: 8D treatments than in 24L: 0D and 0L: 24D. Additionally, activities of intestinal amylase (AMS) lipase (LPS) pepsin (PPS) and trypsin (TPS) in the stomach were significantly higher in the 8L: 16D, relative to the other treatment groups. Gills of juveniles exposed to 0L: 24D recorded significantly higher catalase (CAT) and superoxide dismutase (SOD) activities, compared to those in the other groups. Regarding the dorsal muscle, a significantly higher CAT activity was recorded under 0L: 24D light than the other light photoperiods. Moreover, kidneys of juveniles exposed to 24L: 0D recorded the highest CAT and SOD activity. In summary, 8L: 16D, 12L: 12D, and 16L: 8D light photoperiods increased the digestive enzyme activity, reduced oxidative stress, and enhanced growth in fish, despite long-term exposure to light or darkness being unsuitable. These findings indicate that light and dark combinations are more conducive for culturing sea bass, with the 8L: 16D regime being the optimal photoperiod for the growth of juveniles.