COMPARATIVE STUDY OF SCOMBROID FISHES. 
381 
Biology and Ecology. 
HABIT. 
The scombroid fishes are said to be pelagic, but only the fishes of the 
Plecostei are truly pelagic. The mackerels, Scomber aud Tbastr eiliger, live in 
littoral waters, and most seerfiskes too. The tunnies and bonitos, however, feed, 
spawn, and grow in the open sea. 
Scombroid fishes generally swim to the shallower strata of water at night, 
and return to the deeper layer in day-time, probably following the movement 
of the plankton, and also that of those animals which feed on plankton. Thus 
the twilight is the best time for fishing these fishes. 
Scombroid fishes swim near the surface of the sea, in and after the spawn¬ 
ing season. These fishes are alert and very difficult to catch. They approach 
the shore in warm seasons, and retire to deeper layers of water in off-shore 
grounds in cold seasons. When a southerly wind blows, the common tunny 
comes near the surface of the sea, and also approaches the shore. Until recent¬ 
ly, no drifters for the tunny were found out on the sea, when other winds 
prevailed. Lightning and the sound of thunder are said to frighten tunnies 
and bonitos, driving them into deeper strata of the water. 
Tunnies are often said to resold to the neighborhood of deep rocky banks, 
rising to ca 200 m below the surface. Especially Parathunnus mebachi swim 
in rather deep layers of water, about one hundred metres below the surface. 
Thunnus germo is said to descend to a depth of ca 80 m, while the other tun¬ 
nies can descend to a depth of ca 50 m. In summer, schools of Thunnus ori¬ 
entons and Neothunnus macroyterus sometimes swim with the tips of the dorsal 
fins and the anal out of the water. Bonitos swim quite near the surface of 
the sea, and seldom descend below forty metres. 
Scombroid fishes often leap out of the water, or show the posterior por¬ 
tion of then’ body, especially when they are feeding. Parathunnus mebachi is 
said to have a peculiar habit of leaping out of the water at day-break. 
Scombroid fishes very soon succumb after a violent convulsion, when caught 
and taken out of the water. They are very difficult to keep alive, except the 
common mackerel, as they dart against the fence, when co nfi ned in a narrow 
space, and they can not exist in water of low salinity. Tunnies desert 
