Effects of light intensity on animal husbandry and digestive enzyme activities in sea bass Dicentrachus labrax post-larvae

A 3-week experiment was carried out to investigate the effects of light intensity on animal husbandry performances (mainly growth, survival and cannibalism rates) and their relationships with digestive enzyme activities (pepsin, trypsin, chymotrypsin and amylase) in sea bass post-larvae. Four light intensities (5, 50, 100 and 400 lx) were compared in triplicate. Fish (initial body weight: 34 mg) were automatically fed eight times a day during the daylight period. During the first experimental week, fish were progressively habituated to ingest compound diet by a progressive replacement of Artemia metanauplii by dry food (weaning phase). Survival and cannibalism rates were estimated at the end of the experiment. On Days 0, 7, 14 and 21, post-larvae were collected to monitor growth and to assay enzymatic activities and food consumption. Light intensity did not significantly affect neither survival (25.5-39.4%) nor cannibalism (0.6-1.5%) rates or growth (169-195 mg). Trypsin and chymotrypsin specific activities were affected by light intensity during the weaning period. Significantly lower specific activities rates were obtained in the 5-lx treatment, but this phenomenon was no longer observed after Day 7. Specific activity of amylase was not modulated by light intensity. On the other hand, specific activity of pepsin was extremely dependent on light intensity. In sea bass, this enzyme is functional at the end of the first developmental month and its activity increases with age. In the present experiment, only the light intensity of 50 lx induced this increase at the end of weaning. The increase was delayed to Day 14 in fish reared under 100-lx light intensity. Specific activity of pepsin decreased during the 21 experimental days for 5- and 400-lx light intensities. This induced a delay in the onset of stomach digestion, while digestive performances of sea bass post-larvae were optimized when fish were reared under medium (50-100 lx) light intensity.