Abstract
The relationship between width of line target and distance at the limit of discrimination was examined by means of the conditioned reflex method. Japanese parrotfish Oplegnathus fasciatus as experimental fish and distances from 50cm to 200cm were used. Target board was made of white acrylic resin with a vertical black line in the center. The width of line target was changed from 0.2 to 8.0mm.
The width of line target at the limit of discrimination increased exponentially with an increase in the distance. The width of line target φ (mm) at the limit of discrimination was shown to be an exponential function of the distance L (cm) as follow, φ=exp (1.768 10-2 L-2.287)
