The question of the level at which the fish swim,, that is 

 the vertical distributions is treated in a later chapter^ but 

 it differs with the specieso Furthermorej, for the same species 

 it varies with the season and the areao It is thought that the 

 factors controlling vertical distribution are probably tempera- 

 ture and the strength of the light raysp however,, when it comes 

 to the point of which of these factors is the most significant » 

 it appears that this also differs with the area and no generally 

 conclusive statement can be madoo 



Dro Kishinouye has given a diagram of the vertical 

 distribution of the tunas in Japanese v^aterSp the essentials of 

 which are as followso The basis for these figures is not 

 indicated^ but probably they were calculated from the construc- 

 tion of the longlines used by fishermenc 



albacore 0-80 meters 

 black tuna 0-58 meters 

 big-eyed tuna = 58 meters 

 yellowfin tuna = 57 meters 



Bo Taxonomy 



The number of kinds of tuna that occur throughout the whole world 

 is very large ^ but it is thought that among them there are quite a few 

 which are the same species under different nameso The following five 

 species are the ones which occur in Japanese waterso Not a few scholars 

 take the view that the majority of these are cosmopolitan species and 

 that they are identical with the species of the Atlantic regiono The 

 author himself supports this view^ with the proviso that there should 

 be ample comparative study. 



There is a detailed study by Dr^ Kishinouye of the five species 

 which occur in Japanese waterSo He combined the families Thunnidae and 

 Katsuwonidae to form the Order Plecostei,, separating them from the 

 Order Teleosteic. The basis of his theory was the presence of a cutaneous 

 vascular system in these fishes sind the location of the so-called chiai 

 /o^ark muscle tissue/ close to the vertebral columno However^ Drc Takahashi 

 Ci924) pointed out the presence of cutaneous vascular systems in many 

 other teleosts and proved that there was no reason for establishing the 

 Plecostei^ 



At present the Plecostei is not adopted in the scientific worlds 

 but Dro Kishinouye 's studies of the scombroids have lost none of their 

 valueo 



The taxonomy in this book is based on Kishinouye' s with reference 

 to the theories of other scholarSo 



25 



