Screening Relaxants for Efficacy and Effects on Growth for Greenlip Abalone, Haliotis laevigata Donovan

Relaxants are used in abalone aquaculture to facilitate handling, transport and grading stock, with minimal injury, stress, immune suppression and mortality. Benzocaine has been commonly used as an abalone relaxant but negative behavioural responses to exposure have been observed, and in some countries it has a withholding period, precluding its use for rested harvest, so alternatives are needed. We screened seven candidate relaxants (propylene phenoxetol, magnesium sulphate, magnesium chloride, tricaine methanesulphonate (MS-222), clove oil, AQUI-S and 2-phenoxyethanol) and benzocaine on small (1 year old, 18–28 mm shell length) greenlip abalone (Haliotis laevigata Donovan). We determined the effect of a range of concentrations of each product on abalone and assessed relaxation and recovery times and behavioural responses to exposure to the relaxants. The effect of exposure to these products on abalone growth was evaluated over 90 days after immersion treatment. Adverse effects on behaviour, foot colour, ease of release, relaxation and recovery time, survival or growth were seen using MgSO₄, MS-222, clove oil, AQUI-S and benzocaine. Three products (2-phenoxyethanol, propylene phenoxetol and MgCl₂) met criteria for practical use and are candidates for further investigation for use as relaxants for greenlip abalone aquaculture.