Bacterial strain PM-4, isolated from a crustacean culturing pond, improved the growth of crab (Portunus trituberculatus) larvae and repressed the growth of Vibrio anguillarum in seawater. PM-4 was cultured in a large quantity and was added daily for 6 d to 200 m3 of seawater used for culturing crab larvae. Initial bacterial density in the crustacean culture water was 106 cells/mL When bacteria increased to more than 107 cells/mL (at crab larval growth stage zoea II), the protozoan population, primarily flagellates, grew rapidly and reduced bacterial numbers to 106 cells/mL Among the bacterial assemblages monitored, added PM-4 dominated the bacterial populations, i.e. Vibrio spp. numbers decreased or even became undetectable in seawater. Production of crab larvae was greatly increased by adding bacterial strain PM-4 to their culture water.

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Since 1985, frequent mass mortalities due to a bacterial infection have occurred in zoeal larvae of swimming crab Portunus trituberculutus reared at the Tamano Station of the Japan Sea-Farming Association. A bacterium was predominantly isolated from diseased larvae and was demonstrated by experimental infection to be the causative agent of the disease. Based on morphological, physiological, biochemical, serological and genetic characteristics of the pathogen, it was thought to be a new species and tentatively named Vibrio sp. Zoea. Challenge experiments with the bacterium in several aquatic animals indicate that Yibrio sp. Zoea appears to be a pathogen specific for crustaceans.

EŠect of temperature on survival and developmental period of larval snow crabChionoecetes opilio (Brachyura: Majidae) reared in the laboratory TAKAYUKI KOGANE, 1 KATSUYUKI HAMASAKI 2a AND KINYA NOGAMI 1b