394 KAMAKICHI KISHTNOUTE : 



ENEINOES AND PARASITES. 



The gigantic species of the scombroid fishes have few enemies. Tiieir most 

 dreaded enemies are dolphins, especially the kiUer. Killers often await the 

 passage of large schools of tunnies in a strait, such as Tsugaru Strait, and 

 attack them furiously. Favourite resorts of killers in the strait are near Cape 

 Oma and Cape Tappi. Small species and immature forms, however, have many 

 enemies — seals, dolphins, spear-fishes, the swoid-fish, sharks, and larger forms 

 of their own or alUed species. When we find dolphins in places, where mack- 

 erel fishing is actually canied on, the mackerels very soon desert the gi'oimd, 

 and do not come back for some days after. 



External parasites are mostly copepods and trematods. They are found 

 on the upper surfcice of the pectoral fin, the inner side of the opercle, gill- 

 lamellae, in the nasal cavity, the mouth cavity, etc. These parasites are, 

 as a rule, not numerous ; but sometimes copepods are found in large batches. 

 The Odocoiyle is a minute parasite found among the giU-lamellae of Scomhei' 

 japonicus, but the Hexacotyle is large and is found among the gill-lameUae 

 of Parathtmnns mehachi. Tiistommn Uves in the nasal cavity of tunnies. 



Internal parasites are chiefly trematods and nematods, living in aliuientary 

 caual, circulatory system, muscles, tissues of the viscera, etc. Species of Didoma 

 rise AcanViocyhium, tunnies, and bonitos as hosts. Ehynclidbothrium is found in 

 the flesh of Katsmvontts pelamis rather abimdantly in summer. A species of the 

 Filariadae generally inhabits the superficial dark red muscle of Paraihwmns 

 mehachi. The parasite changes the colour of the muscle, which becomes more 

 or less yellowish. Once I found a very long nematod in the cutaneous artery 

 of EidliyniiKs yaito. Often a species of nematod is found in the dorsal aorta 

 of Neothuimus macropiervs ; the parasite causes the tissue of the canal to bei'ome 

 thick and tough, giving it at the same time a yellowish tint. 



FISHERY. 



Fishing of the scoml)roid fishes has Ixxm jjursucd in our islands since 

 the stone age. Bones of these fishes have been found in shell-mounds in 

 different localities of our empire, as I have said already in a paper on the 

 preliistoric fishing of our counti-y (42). Bones of Thminns orientalis are most 

 abuudaut, and those of Knlsuivo7W.s jielamis and Scomber japonicus are fi-equently 



