イシダイ仔稚魚の成長に伴う走光行動の変化

Abstract

The change in phototactic response of the striped beakperch Oplegnathus fasciatus and the preferred illuminance level were investigated. Furthermore, the occupation limit from bright-ness into darkness was also examined. Larvae one day after hatching, with a total body length of 2.1mm, floated near the sea surface, but eyed larvae two days after hatching, with a length of 2.4mm, migrated to the brighter water area when they were in an illuminance of less than 2, 500lx. Larvae at this stage already had a noticeable phototactic response. Juveniles 25 days after hatching, with a length of 10 to 14mm, and 45 days after hatching, with a length of 18 to 22mm, gathered in the brighter water area during the low illuminance level from 90 to 750lx, while at an illuminance of more than 2, 800lx their behaviour was distracted. In this stage of juveniles, an illuminance level of 750 to 1400lx was favored. The occupation of juveniles from brighteness into darkness was limited by the horizontal gradient of illuminance, and the value of gradient that they could not enter was anything over 3%/cm.