ABSTRACT
Flatfi sh (Pleuronectiformes) are a group of teleosts. They have the most extremely asymmetrical body of all vertebrates: both eyes lie either one side of the head (Kyle, 1923; Norman, 1934; Hubbs and Hubbs, 1945; Policansky, 1982a; Ahlstrom et al., 1984). In the same species, usually the eyes are always either on the right side of the head (dextral) or on the left side (sinistral). The two species of very primitive genus Psettodes are the only fl atfi sh in which the eyed-side is indiscriminately determined in each individual, and hence, there are both dextral and sinistral fi sh within the same species. (Hubbs and Hubbs, 1945; Ahlstrom et al., 1984). In the starry fl ounder, Platichthys stellatus, there are also both dextral and sinistral fi sh. However, the eyed-side is not randomized as Psettodes but depends on the location where the fi sh lives. Off the US coast they are nearly half sinistral and half dextral. In the middle of the US and Japan, off Alaska, about 70 percent of them are sinistral, and in Japanese waters nearly 100 percent are sinistral (Policansky, 1982a).
