1962 年 8 巻 5-6 号 p. 126-146
1) Comparative studies have been made on the three species of the genus Parasilurus found found in Lake Biwa-ko, both from the morphological and the ecological points of view. Proportions are examined for various parts of body, and the external characters of sensory organs and of certain feeding organs are scrutinized.
2) The results obtained from these studies may be summarized as follows: in P. biwaensis, the development of external sensory organs is rather poor except for eyes, and the body as a whole is adapted for pelagic carnivorous life ; in P. lithophilus, sensory organs are well developed, and the body is adapted to a good extent for rupicolous life ; in P. asotus, two pairs of heavy barbels present, whereas the eyes are degenerated, and the body is adapted for bottom life in shallow turbid water.
3) Percentages of the lengths of eight body parts against standard length are illustrated in graphs, and the types of their growths are compared. It may be seen from these graphs that specific difference is hardly found in some characters but is notable in the others. Moreover, the latter characters become divergent among species according to their growths.
4) Irrespective of superficial variability of P. asotus, its specific peculiarity has become evident after many characters have been examined as a combination. Such a combination of characters is always peculiar to P. asotus and is correlated with the mode of its life, though respective characters are not stable according to the difference in external factors. Not giving proper consideration for ecological data, we might fail in realizing the accurate status of P. asotus, being only perplexed by its variable faces.
5) Besides the differences mentioned above, there is another type of differenti ation among the species found in Lake Biwa-ko. This is the discrepancy in vomerine tooth-band, whose shape is always fixed in each species. The difference is, however, variable to a considerable extent in specimens taken from waters other than Lake Biwa-ko.
6) Mere comparisons of specimens from various localities are of little importance, unless studies on habitats and life will be carried out. Future investigations in this line should be necessary on such problematical species of the genus Parasilurus as are spread over the Asiatic Continent.
7) In clarifying the origin of the three species occurring in Lake Biwa-ko, it is necessary to investigate the topographical histories of the habitats of the respective species, besides researches for their habitats of the present day.
8) It may be needed to conduct in future investigations on the developmental stages (etap) of the fishes.