6 March 2009 Table 2. Comparison of different stress indicators in fish exposed to different photoperiods with levels observed in stressed fish Parameters Control Stressed Values from different photoperiods values values1 6L:6D 12L:12D 16L:8D 24L:0D Cortisol (ng/mL) 6.7 190.1 7.7 7.1 7.4 7.7 Glucose (mg/100 mL) 69.2 109.5 76.4 73.6 70.8 72.9 Protein (g/100 mL) 3.8 3.0 4.8 4.3 4.6 4.3 Cholesterol (mg/100 mL) 237 180 246 244 238 248 1Biswas et al. (2006a) stress, a number of stress indicators were investigated. The results are summarized in Table 2, where the values of different stress indicators observed in this study are compared with stress-induced levels (Biswas et al. 2006a). The results demonstrate that the levels of different stress indicators in fish exposed to the 24L:0D were far lower than the stress-induced levels. Although stress has been demonstrated to reduce food intake and growth rate in different fish, red sea bream exposed to 24L:0D showed neither a decreased growth rate nor reduced food intake compared to those exposed to 12L:12D. Therefore, photoperiod manipulation did not cause a noticeable stress response in red sea bream when reared under different artificial photoperiods. In growout farms, photoperiod manipulation can be used to hasten growth rate and has been practiced in many countries in recent years. The main concern is how the different photoperiods could be controlled in outdoor farms. Some possible ways were discussed by Bromage et al. (2001). Generally, this involved the installation of light-proof covers over culture units and the provision of artificial lighting controlled by automatic time clocks. The heavy-duty polythene or butyl linings are suspended over a simple metal, plastic pipe or wooden framework providing a cheap and effective method of blacking-out the desired areas. Tungsten or fluorescent sources of illumination can be used, preferably with a spectrum as close as possible to that of natural light. The lights should provide intensities of at least 100 lux at the water surface in all areas of the enclosures. Intensities less than 20 lux should be avoided inasmuch as they may lead to inconsistent results. To reduce stress from abrupt changes in light at the switch-on and switch-off times, fluorescent lights may require a second system of less bright lights to be installed, which are switched on shortly before and after the main system and, hence, provide the necessary twilight periods. In conclusion, the growth performance of juvenile red sea bream reared from 20 to 100 g can be stimulated remarkably by using a continuous (24L:0D) photoperiod without any adverse effect on physiology. Biswas et al. (2006b) demonstrated that the growth performance of red sea bream, when reared from 1 to 30 g, can also be stimulated. These results together help to establish a light regime giving optimal fish growth for a complete production cycle of red sea bream. It is assumed that more attention will be given to indoor and outdoor culture in the near future. Photoperiod manipulation will definitely be the option of choice to get higher output from those types of systems. Notes 1Fisheries Laboratory, Kinki University, Uragami, Nachikatsuura, Wakayama 649-5145, Japan. Corresponding author e-mail: ns_ akb@nara.kindai.ac.jp; Fax: +81 735 58 1246 2Kansai Electric Power Co. Inc., Nakanoshima 3-6-16, Kita-ku, Osaka 530-8270, Japan 3Matsushita Electric Works Ltd., Osaka, Japan. Acknowledgments This study was financially supported by the 21st Century COE program of the Ministry of Education, Culture, Sport, Science and Technology, Japan. The expenses were defrayed in part by a grant from Kansai Electric Power Corporation, Japan. References Biswas, A. K., M. Seoka, K. Takii, M. Maita and H. Kumai. 2006a. Stress response of red sea bream Pagrus major to acute handling and chronic photoperiod manipulation. Aquaculture 252:566572. Biswas, A. K., M. Seoka, Y. Tanaka, K. Takii and H. Kumai. 2006b. Effect of photoperiod manipulation on the growth performance and stress response of juvenile red sea bream (Pagrus major). Aquaculture 258:350-356. Biswas, A. K., M. Seoka, Y. Tanaka, K. Takii and H. Kumai. In press. Use of photoperiod manipulation to stimulate the growth performance of juvenile red sea bream (Pagrus major). World Aquaculture. Boeuf, G.. and P. Y. Le Bail. 1999. Does light have an influence on fish growth? Aquaculture 177:129-152. Bromage, N. R., M. Porter and C. F. Randall. 2001. The environmental regulation of maturation in farmed finfish with special reference to the role of photoperiod and melatonin. Aquaculture 197:63-98. Johnsson, J. I. and B. T. Björnsson. 1994. Growth hormone increases growth rate, appetite and dominance in juvenile rainbow trout, Oncorhynchus mykiss. Animal Behavior 48:177-186. Murata, O., T. Harada, S. Miyashita, K. Izumi, S. Maeda, K. Kato and H. Kumai. 1996. Selective breeding for growth in red sea bream. Fisheries Science 62:845-849. Taniguchi, N., S. Matsumoto, A. Komatsu and M. Yamanaka. 1995. Difference observed in qualitative and quantitative traits of five red sea bream strains propagated under the same rearing conditions. Nippon Suisan Gakkaishi 61:717-726.
RkJQdWJsaXNoZXIy MjExNDY=