Faculty of Fisheries, Kagoshima University, Kagoshima, Kagoshima 890-0056, Japan
Wavelength specific phototactic responses to monochromatic light in loggerhead and green turtle hatchlings and the presence of three visual pigments in loggerhead turtle are well known, and both indicate the possession of color sense in marine turtles. We conducted classical conditioning in indoor tanks to examine the color sense of loggerhead turtle. Three 23-day old hatchlings and a 3-year old (3-y) specimen were conditioned for food on the presentation of green and red panels for the former, and green and black balls for the latter, and then they were exposed to transposition tests in which the respective negative conditioning color was transposed with gray of three different darknesses. In the transposition tests, the 3-y specimen showed an absolute choice to green to which the specimen was initially conditioned, indicating the possession of color sense. The hatchlings showed inconsistent choices with 40 to 100% correct responses regardless of darkness of the transposed gray colors, indicating an immature color sense in them.