Acetic acid immersion – A reactive pest treatment for bivalve aquaculture

Unwanted biofouling and predatory pests are a universal problem threatening aquaculture productivity and profitability. Various control approaches have been trialled, but industry uptake has been elusive due to the typically fine balance between pest and bivalve physiological tolerances (i.e., ‘therapeutic window’) and operational challenges related to infrastructure, scalability, and quality control. This study aimed to address these factors for acetic acid (AcOH), arguably the best-studied and most broadly applicable reactive treatment for bivalve aquaculture. Using case studies of farmed New Zealand green-lipped mussels (Perna canaliculus Gmelin 1791) and Pacific oysters (Crassostrea gigas Thunberg 1793), AcOH tolerances of various size classes of these bivalves were determined in a series of laboratory experiments, and cross-referenced to corresponding data for biofouling and predatory pests. Resulting ‘therapeutic windows’ formed the basis of provisional treatment parameters, being 2% AcOH for 60 s or 4% AcOH for 30 s for P. canaliculus and C. gigas, respectively. Three independent field experiments on operational P. canaliculus and C. gigas farms subsequently served to refine and validate the treatment parameters and associated operational procedures. For P. canaliculus, AcOH treatment had overall positive impacts on commercially relevant measures of aquaculture production, with the best performing treatment regimens of 1% or 2% AcOH for 60 s resulting in almost three times as many individual P. canaliculus per section of growing rope. Incorporating a subsequent air-drying step was also shown to reduce required AcOH immersion times, providing opportunities to enhance operational efficiencies via more rapid treatments. The provisional treatment parameters for C. gigas of 4% AcOH for 30 s were also highly effective against biofouling pests in the field and resulted in no detectable mortality of the culture species. Overall, this study demonstrates the utility of carefully refined and validated AcOH treatments to control problematic pests in bivalve aquaculture. It is essential to accurately determine ‘therapeutic windows’ for any given bivalve culture species and developing understanding of crop-pest interactions would better inform treatment timing and frequency. Such approaches could feed into wider frameworks to optimally manage pests below economically damaging thresholds, with AcOH ideally being one option in an arsenal of management interventions.