4 March 2009 Continuous photoperiod can be used to get higher growth performance in juvenile red sea bream (Pagrus major) Amal K. Biswas*1, Manabu Seoka1, Yoshimasa Tanaka2, Kiyotaka Ueno2, Kenji Takii1, Hidemi Kumai1 This report is one of a series of articles devoted to establishing a light regime that will promote optimal growth for a complete production cycle of red sea bream, Pagrus major (Figure 1). This is one of the most important fish in Japan because of its multipurpose uses as sashimi, sushi or presented in ceremonies such as weddings, where it is seasoned with salt and grilled. There is a growing concern as to how the production of this commercially important fish can be enhanced. Photoperiod manipulation has proven to be a more economic way of stimulating growth performance in this species without adverse affecting its physiology when reared from 1 to 30 g (Biswas et al. 2006a,b; Biswas et al. in press), and has also been effective when used with other species (Boeuf and Le Bail 1999). This article shows a positive effect of photoperiod manipulation on the growth performance of red sea bream without a stress response when reared from 20 to 100g. Photoperiod Design Four different light regimes were established (Figure ２): 6 h light:6 h dark (6L:6D), 12 h light:12 h dark (12L:12D), 16 h light:8 h dark (16L:8D) and continuous light (24L:0D). A programmed time controller3 was used to maintain the periods of light and dark, including dimming over 30 minute periods. Three tanks in each treatment were illuminated with one 40 W fluorescent tube suspended 45 cm above the water surface. Light intensity was maintained at 1500 lux Fig. 1. Red sea bream (Pagrus major) on the water surface throughout the experiment. Each set of three replicates was isolated from the other set and from stray light by shielding with an opaque partition. Fish and Experimental Design Juvenile red sea bream (body weight 10-30 g) of the Kinki University strain (Taniguchi et al. 1995, Murata et al. 1996) were obtained from the Fish Nursery Center of Kinki University, Uragami, Japan and acclimated to the new rearing environment. During the acclimation period, photoperiod in all tanks was set at 12L:12D. The tanks were supplied with filtered seawater and aerated to maintain the oxygen level near saturation. The water flow was 5 L/min and the temperature was maintained at 21±1°C throughout the rearing period. After conditioning for one week the fish were exposed to the test photoperiods at a density of 32 fish in each of three replicates (200 L) for each treatment. The initial mean body weight was approximately 20 g. Fish were fed a commercial diet to apparent satiation for eight weeks according to the feeding schedule presented in Figure 2. Individual body length and weight were taken at the end of the trial to calculate the growth performance. Blood samples were also taken to investigate the levels of stress indicators in the plasma. To investigate the effect of photoperiod manipulation on the digestive performance of red sea bream, fish were reared for another three weeks and fed a diet containing 0.5 pecent chromic oxide (Cr2O3) using to the feeding schedule in Figure 2. Fig. 2. Feeding schedule in different photoperiods. Arrow indicates the time of feeding and the black bar shows the dark phase of the photoperiod.
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