東北日本におけるウグイ属魚類の種族分化

Morphological and morphometrical studies were performed to elucidate the speciation and racial differentiation of the fish belonging to the genus Leuciscus (=Tribolodon), in addition to the revisional examination of the cephalic lateral-line system as an ideal character for the classification of this group of fish proposed by NAKAMURA (1963, 1969). The materials were collected from various rivers, streams and lakes, ranging from the southern part of Hokkaido to the north of Nagano Prefecture. The present investigation confirmed roughly the results of NAKAMURA (1963, 1969), and the Japanese dace were classified tentatively as follows: Leuciscus brandti (=L. jusanensis, very probably), superspecies, sea-run form. L. hakonensis, sea-run form and freshwater form. L. ezoe, freshwater form. L. taczanowskii ?, sea-run form, found probably in the Pacific side. L. sp. (Nom. Jap.: Ukekuchi-ugui. Uke-kuchi means the feature of the mouth part, showing the protruded lower jaw) freshwater form, found exclusively in the River Agano. It is of interest to know that the individuals with larger number of scales on the lateral line, such as L. jusanensis and L. sp., posses also the larger number of scales before dorsal fin. As stated previously (NAKAMURA, 1963, 1969), by the features of cephalic lateral-line system, the fish were classified into two major groups, such as the A and B types. In the A (L. jusanensis and L. taczanowskii) with larger number of scales on the lateral line, there is found a junction between the postocular commissure (POC) and preoperculomandibular canal (POM), while in the B (L. hakonensis, L. ezoe and L. sp.) no junction is detected between the POM and POC. When the pores of POM were counted, the number in L. hakonensis and L. ezoe is concentrated in 13, while that of the rest three races is in 20. In the case of the pores of supratemporal canal (ST), the number in L. hakonensis and L. ezoe is fewer than that of the rest (more than 9). However, there is a variation of the number of ST in some populations of the sea run form of L. hakonensis, 6 to 8. The secondary sexual characters, such as the features of nuptial coloration and pearl organ, differ among different races. Therefore, it is considered that these characters are intrinsic for each race and useful for classification of mature adult dace. L. sp. (Ukekuchiugui) found exclusively in the Agano River system is a peculiar race in having the mixture of morphometric characters of different races. Further studies including comparative endocrinology are now in progress to clarify the adaptability and evolution of the Japanese dace.