Abstract
In Toyama Bay, catch of sandfish, Arctoscopus japonicus, has decreased dramatically. The authors have reared brood stock of the deep-sea (cold water) species using pumped deep seawater assuming the release of mass juveniles. As reported previously, we have already succeeded in collecting eggs from reared 1-year-old brood stock in tank. In the present study, the following trials were made to obtain mass eggs; continuing culture of the used brood stock (continuously-reared group, N=200) in 4kl tank and mass production of 1-yearold brood stock (mass production group, N=3, 250) in 33kl tank. These brood stock cultures resulted in production of 189, 400 eggs in prolonged spawning periods (2 to 3 months). Most of these eggs were kept in surface-sea water to control water temperature (elevating from 4 to 12°C via 7 and 10°C) during egg incubation. As the result, we could concentrate hatching at the expected timing (last week of December) to start the seedling production from the larvae earlier than the usual trial by two months. Furthermore, by culturing the larvae in landbased tank and subsequently in sea-based net cages, we could obtain larger seedlings by 30 mm in total length in May. Some problems, including prolonged spawning periods, low spawning rates (=number of females spawned per stocked) (20-43%), low eyed-egg rates (47-73%), low hatching rate (27%) and high initial dropout (>98% of dead juvenile in two weeks) during seed production were pointed out and discussed in relation to the culture conditions.
