Department of Aquatic Biosciences, Tokyo University of Fisheries, Minato, Tokyo 108-8477, Japan
This experiment was conducted to determine the sensitivity of two different strains of tilapia Oreochromis niloticus (G8 and J1 strains) to infrared light using a rotating striped drum. Two hundred fish (TL 3-4cm) of each strain were exposed to five wavelengths (visible rays and those over 700, 750, 780, and 800nm) using filters. All of the fish showed the same sensitivity to visible as well as light over 700nm. Ten percent of the fish among the G8 strain could sense light over 780nm. None of the fish in the other strain (J1 strain) could sense light over 750nm. However, wavelengths over 800nm did not elicit a response in either strain. It is concluded that 1) a straindifference exist among tilapia with respect to infrared light sensitivity, and 2) at least one strain (G8 strain) of tilapia can sense infrared light in the range of 780-800nm.