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 int ensity on animal husbandry performances (mainly growth, survival and cannib alism rates) and their relationships with digestive enzyme activities (peps in, trypsin, chymotrypsin and amylase) in sea bass postlarvae. Four tight i ntensities (5, 50, 100 and 400 lx) were compared in triplicate. Fish (initi al body weight: 34 mg) were automatically fed eight times a day during the daylight period. During the first experimental week, fish were progressivel y habituated to ingest compound diet by a progressive replacement of Artemi a metanauplii by dry food (weaning phase). Survival and cannibalism rates w ere estimated at the end of the experiment. On Days 0, 7, 14 and 21, post-l arvae were collected to monitor growth and to assay enzymatic activities an d food consumption. Light intensity did not significantly affect neither su rvival (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 inten sity during the weaning period. Significantly lower specific activities rat es were obtained in the 5-lx treatment, but this phenomenon was no longer o bserved after Day 7. Specific activity of amylase was not modulated by ligh t intensity. On the other hand, specific activity of pepsin was extremely d ependent on light intensity. In sea bass, this enzyme is functional at the end of the first developmental month and its activity increases with age. I n the present experiment, only the light intensity of 50 Ix induced this in crease at the end of weaning The increase was delayed to Day 14 in fish rea red under 100-lx light intensity. Specific activity of pepsin decreased dur ing the 21 experimental days for 5- and 400-lx light intensities. This indu ced 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. (C) 2001 Elsevier Science B.V. All rights reser ved.