Biocontrol method in aquaculture for rearing the swimming crab larvae Portunus trituberculatus

The aim of this work is to control the water environment for culturing larvae of the swimming crab, Portunus trituberculatus, using microorganisms. The bacterial strain PM-4 (Thalassobacter utilis) improved the survival rate of crab larvae and repressed the growth of Vibrio anguillarum (bacterium) and Haliphthoros sp.(fungus) in seawater. PM-4 was cultured and added daily to seawater during the first to third zoean growth stage of the crab with diatoms and rotifers. Numbers of PM-4 decreased in. culture water during the first 3 days, because of feeding by the first zoean stage of larvae. The final concentration of PM-4 was 10(5) to 10(6) cells ml(-1) according to the plate count method in larval, rearing water. During 1989 to 1993, we tried seed productions of a swimming crab in 200 m(3) containers at Tamano Station, Japan Sea-Farming Association. In 33 trials of the biocontrol methods, average survival rate of crab larvae was 28.3% when the bacterial strain PM-4 was added. In 42 trials in which the strain PM-4 was not added, average survival rate of crab larvae was 15.6%. We conclude that the bacterial strain PM-4 is effective as a biocontrol agent.