Department of Aquatic Biosciences, Tokyo University of Fisheries, Minato, Tokyo 108-8477, Japan
This study investigated the postural control in tilapia Oreochromis niloticus under near infrared light irradiated conditions at microgravity. Parabolic flight experiments using aircraft were conducted with juvenile tilapia (TL 3-4cm) that were accommodated in airtight tanks irradiated near infrared light (wavelength 880±40nm) from bottom to top. The swimming behavior was visualized by infrared CCD video cameras and recorded in videotapes. Six fish among 55 (10.9%) showed normal swimming and they turned their dorsal side to the infrared light source (dorsal light response). Percentage of time the fish spends with dorsal side towards the light source to normal swimming time was 74.4±22.5%(n=6). The result shows that the normal swimming individuals control their posture depending on infrared light. Thus, a population of tilapia can sense near infrared light similar to that under a visible light irradiated condition.