394 
KAMAKICHI KISHINOUYE : 
ENEMIES AND PARASITES. 
Tlio gigantic species of the scombroid fishes have few enemies. Their most 
dreaded enemies are dolphins, especially the killer. 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 
Öma and Cape Tappi. Small species and immature forms, however, have many 
enemies—seals, dolphins, spear-fishes, the sword-fish, sharks, and larger forms 
of their own or allied species. When we find dolphins in places, where mack¬ 
erel fishing is actually carried on, the mackerels very soon desert the ground, 
and do not come back for some days after. 
External parasites are mostly copepods and trematods. They are found 
on the upper surface 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 Octocotyle is a minute parasite found among the gill-lamellae of Scomber 
japonicus, but the Hexacotyle is large and is found among the gill-lamellae 
of Parathunniis mebachi. Tristornum fives in the nasal cavity of tunnies. 
Internal parasites are chiefly trematods and nematods, living in alimentary 
canal, circulatory system, muscles, tissues of the viscera, etc. Species of Distoma 
use Acanthocybiurn, tunnies, and bonitos as hosts. BhynchobotJirium is found in 
the flesh of Katsuwonus pelamis rather abundantly in summer. A species of the 
Filariadae generally inhabits the superficial dark red muscle of Parathunnus 
mebachi. 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 Euthynnus yaito. Often a species of nematod is found in the dorsal aorta 
of Neothunnus macropterus ; the parasite causes the tissue of the canal to become 
thick and tough, giving it at the same time a yellowish tint. 
FISHERY. 
Fishing of the scombroid fishes has been pursued 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 
prehistoric fishing of our country (42). Bones of Thunnus orientalis are most 
abundant, and those of Katsuwonus pelamis and Scomber japonicus are frequently 
