1Obama Station, National Center for Stock Enhancement (NCSE), Fisheries Research Agency (FRA), Obama, Fukui 917-0117, 2Department of Marine Biosciences, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, 3Yaeyama Station, Stock Enhancement Technology Section, Ishigaki Tropical Station, Seikai National Fisheries Research Institute, FRA, Ishigaki, Okinawa 907-0451, Japan
Behavioral characteristics of snow crab Chionoecetes opilio larvae such as phototaxis and geotaxis in relation to their depth regulation were examined in the laboratory. Further, effects of agitation and bath treatment with sodium nifurstyrenate (NFS-Na) for larval rearing water on survival rates of larvae, rates of larvae which floated in the rearing water, and mortality rates of larvae which sunk to the bottom of the tank were investigated. The first stage zoeas floated in the upper layer of the rearing chamber showing positive phototaxis and negative geotaxis, however, almost all larvae of the later stages showed no reaction to a light stimulus and sunk to the bottom of the chamber. Larval floating rates and survival rates were improved by agitation and bath treatment with NFS-Na for rearing water; especially, survival rates significantly increased in the tanks with NFS-Na bath treatment.