Abstract
To investigate the possibility of using deep seawater for rearing Japanese sandfish (Arctoscopus japonicus) for brood stock and to obtain basic knowledge for promoting the brood stock management, spawning, effect of diets on growth and maturity and changes in gonad conditions of the fish were examined from June to December in 1999. The mean To investigate the possibility of using deep seawater for rearing Japanese sandfish (Arctoscopus japonicus) for brood stock and to obtain basic knowledge for promoting the brood stock management, spawning, effect of diets on growth and maturity and changes in gonad conditions of the fish were examined from June to December in 1999. The mean temperature of the deep seawater used was around 5°C.
In the spawning test, 84% of the fish survived, and 43% of the females spawned from October to November. Their first spawning was 2 months earlier than that of the wild ones.
The growth of the fish of experimental Group A, which were fed on a dry diet, was almost the same as that of Group B, which were fed on a fresh diet, but the maturity rate of Group A was superior to that of Group B. The maturity rate of the females of Group A was 77% versus 33% of Group B.
G.S.I.(gonad weight/body weight excluding the internal organs×100)did not change in most of the fish from June to July, but afterwards it increased in more than half of the fish. The mean total length of mature females and males were 15.5cm and 13.8cm, respectively. These lengths nearly coincided with the size of the smallest mature wild fish.
Thus, these investigations proved that the brood stock management of this species using deep seawater is possible and suggested that some rearing conditions in deep seawater would hasten the spawning time. This will be very effective to reduce the mortality of the released fish, because the size of young fishes produced from the brood stock will be larger than that of the wild ones when they migrate to the sea after release. This study also suggests that in order to raise the spawning rate, a suitable diet must be chosen, and the growth of the fish should be promoted so that they can get mature by August.
