抄録
The writer examined the digestive tract and its contents to study the feeding habit of adult forms of two kinds of cods, viz., Gadus macrocephalus (J. N. Madara) and Theragra chalcogramma (J. N. Suketô), both of which were collected during the summer of 1933 in Bristol Bay. The former species being, as is shown in the Table 2, exceedingly voracious, feeds greedily upon the bottom creatures, such as crabs, sand-living worms etc.. Fishes, such as Suketô and several flat-fishes, are also very often eaten by the cod. The fact that a cod feeds on the other kind of cods is worthy of attention and noted here again, although similar cases have been observed and reported by some authors (3, 6, 7, 8, 9, 10, 11). The latter species, on the contrary, as is shown in the Table 4, is poor feeder and feeds upon creatures of small size and the plankton, such as copepods and small shrimps.
Thus, these two cods show essential difference in their feeding habit. As the cause of such a difference, the fact may be noted that the former species lives near the bottom of the sea, while the latter in the middle or the upper layer of the water. And at the same time, it would be worth mentioning that the construction of the digestive systems of the two species shows different features; in the former species the apparatuses for seizing the food (the mouth, the teeth and the tongue) and the organs of digestion (the stomach, the digestive mucous membrane, the vascular supply on the stomach and the pyloric appendages) are all well developed, while in the latter not so. It is also of interest that the former species has coarse gill-rakers which cannot collect fine food such as the plankton, while the latter has fine ones which are favourable to retain it.
