Physical eradication of small planktonic crustaceans from aquaculture tanks with cavitation treatment

Small planktonic crustaceans cause serious problems in invertebrate aquaculture tanks through predatory damage or competition for food resources with the aquaculture species. In sea cucumber aquaculture, they can cause the mass loss of culturing jeveniles for releasing, which is a major obstacle to stable seedling production. In this study, we developed a novel method for eradicating small planktonic crustaceans using a ‘cavitation’ shock wave. Cavitation can cause significant damage to the surfaces of metallic devices, such as propellers and pumps, via the shock waves that occur with the disruption of micro/nano-bubbles. Therefore, we subjected planktonic crustaceans, mainly copepods, to cavitation using a micro/nano-bubble generator. The cavitation treatment reduced the planktonic crustaceans in the aquaculture tanks by 63.3% compared with the control. Comparison of the body size distribution of crustaceans indicated that cavitation treatment kills crustaceans of all sizes equally. We also assessed the negative effects of the micro/nano-bubbles, which are a byproduct of cavitation treatment, on the aquaculture species. We exposed juvenile sea cucumbers (Apostichopus japonicus) and sea urchins (Strongylocentrotus intermedius) to micro/nano-bubbles, and then examined their survival rate four days later; all individuals were intact and uninjured. These results suggest that cavitation treatment is an effective method for controlling planktonic crustaceans without using chemicals.