イトウHucho perryi (BREVOORT) の生活史について

抄録

The life history of Hucho perryi (BREVOORT) was studied in the Faren River in northwestern Nemuro, Hokkaido, from late April to early June, 1960. H. perryi is a salmonid fish, which has flattened head, wide gape with stout teeth, many dark dots on the body and larger scales than those of other salmonid fishes (Pl. 4, A). This fish is distributed in the streams and lakes of Hokkaido, southern Kurile Islands and Sahalin.
From April to May after thawing of ice in the river, this fish is observed in deep pools with rocks or many sunken timbers (Fig. 2), and in June when the water temperature rises about 10°C the fish is found also in the shallow and swift waters as well as deep pools. The stomach contents of 22 specimens, 2.9 to 56.0cm in total length, were examined. The larvae of aquatic insects, especially Plecoptera and Tricoptera, were eaten by the fry from 2.9 to 3.2cm. These diets were occurred commonly in the stomach of juveniles from 14 to 18 cm, and loarch, Barbatura toni oreas (JORDAN and FOWLER), were occasionally found together with the insect larvae. The fish larger than 30cm did not eat the insect larvae but took mainly the loarch. Although chum salmon fry, Oncorhynchus keta (WALBAUM), were found as the same time in the river where the examined fish were captured, they were not eaten by this piscivorous fish.
The spawning season of this fish seems to extend from mid-March after breaking of ice to late April in Nemuro district. The knowledge about maturation was a little. The author obtained three mature males larger than 55cm, and also observed one mature female measuring 93 cm from the Shibetsu River. A spawning redd was found in the tributary pouring into the Furen River at Mimakka (Fig. 3), and 1, 358 eyed eggs in all were taken from this redd on May 22. These eggs were salmon pink in color and measured 5.8 to 6.4mm in diameter. They were brought into the laboratory of Nemuro Branch of Hokkaido Salmon Hatchery, and began to hatch on May 28. The alevins were reared until the yolk sac were completely absorbed.
The newly hatched alevins preserving in 70% alcohol were measured 15.1 to 16.6mm in total length (Pl. 4, D). About 40 days after hatching, the alevins attained to 24.0 to 25.6mm. Two-thirds of the yolk sac were consumed and parr marks began to appear vaguely on the body side (Pl. 5, A). It took 52 days for the alevins to absorb completely the yolk sac at the water temperature of 6.0°to 11.3°C. The fry just after consumed the yolk were measured 28.1 to 28.5mm (Pl. 5, B), and they grew up about 38mm by August (Pl. 5, C).