Abstract
We investigated the survival, growth, and maturity of the rainbow trout Oncorhynchus mykiss reared in deep seawater (DSW) and surface seawater (SSW) pumped from depths of 687 m and 24 m, from Suruga Bay. From November 2006 to April 2007, 52 and 51 fishes (average body weight, 90 g and 96 g, respectively) were reared in heated DSW at a temperature of 15°C and in SSW at natural temperature (12-16°C). As a result, the growth rates of the fishes reared in heated DSW and SSW, were 1.1% and 1.2% per day, respectively, and the survival rates were 48% and 41%, respectively. From February to April 2007, 32 fishes (average body weight, 378 g) were reared in DSW at natural temperature (7°C). The growth rate was 0.0% per day, and the survival rates was 88%. From June 2007, 10 fishes that survived in heated DSW (average body weight, 671 g) and DSW at natural temperature (average body weight, 377 g) were reared in heated DSW (15°C). In November 2007, the average body weight of these fishes was 1.96 kg and 1.29 kg, respectively, and their maturity rates were 71% and 29%, respectively. The fresh meat of mature female fishes was vermilion in color, but that of mature male fishes was a pale beige color. In April 2008, the maximum body weight of fish that survived in DSW at natural temperature was 3.42 kg before maturation. From June 2007, 6 fishes that survived in SSW (average body weight, 883 g) were reared in SSW. However, all the fishes died by the end of July. Although the techniques for restraining the maturation of fishes need to be improved, these findings demonstrate the possibility of rearing large rainbow trout by using DSW.
