An evaluation of the physiological quality of hatchery reared chum salmon fry Oncorhynchus keta

Abstract

In order to estimate the physiological quality of salmon fry for releasing, chum salmon fry were reared under different feeding conditions. Growth, DNA, RNA, protein content, acid protease activity, and swimming ability of the fry were analyzed. The fish reazed at a feeding level of 5% of the BW/day showed normal growth. Those reared at a 1% feeding level showed a slight increase in body weight and protein content. At a 0.5 feedling level, body weight and protein content remained almost constant. Body weight and protein content of starved fish decreased. RNA/DNA and Protein/DNA values of fish reared at a feeding level of 5% of the BW/day were higher than those reared with a limited food supply. Swimming speed of chum salmon decreased in starved fish. A linear correlation was observed between condition factor and swimming speed. Protein content decreased on the 4th week after starvation, when the amount of total protein of chum salmon and the mortality increased coni-cidently. At the same time, the acid protease in the muscle had been activated. Individual size differences for those reared under a feeding level of 0.5% and 1.0%/day (limited food supply) was larger than that of the individuals either starved or reared under a feeding level of 5% of BW. The present data suggests that the requirement for releasing chum fry are a high ratio of RNA/DNA, Protein/DNA, condition factor, and a stronger swimming ability.