1) The influence of the sun-light on the eggs, larvae and fry of Oncorhynchus masou (Brevoort) are studied. 2) The intensity of the sun-light may be effected already upon their chemical compositions in the fry through the oval and larval stages. The fish fed in the lighter place (in the open air out of the hatchery), as compared with the darker place (in faint light inside of the house), are rich in solids, inorganic matters (especially calcium) and nitrogen and are poor in fatty substances. 3) There occur the considarable differenciation in weights of the fish in a group fed on the same diet regardless of the light. And the larger ones are in generally rich in solids especially fatty substances. 4) From these facts, it is concluded as follows:- This species of fishes Oncorkynchus masou (Brevoort) may be already fond of the light place on the youngest days. The fish therefore fed in the open air assimilates the more calcium and nitrogen while that in doors accumulates surplus bodily fats, -these results are the similar to the cases in the preceding report on fasting of salmons fry Oncorlvynclaus keta (Walbaum(1)) in light and darkness.- and the larger ones in a group accumulate in generally the more debot fats without regard of the qauntity of the light.