Effect of movement stress on immune function in farmed Australian abalone (hybrid Haliotis laevigata and Haliotis rubra)

Current abalone mariculture practices include movement of stock to reduce stocking density in tanks and to grade abalone into similar sizes. Australian farmers report that this procedure leads to increased mortality rates in the days following movement. A standard movement procedure as currently done in Australia was investigated on farm as to its effects on haemocyte counts, phagocytic rates, antibacterial activity and lysosomal membrane stability (neutral red retention assay). The experimental design divided the movement process into the main causes of stress, comparing movement without anaesthesia (manual detachment or chipping), anaesthesia without movement and anaesthesia with subsequent movement. Each of the 3 treatment groups had elevated haemocyte counts and depressed phagocytic rates, neutral red retention times and antibacterial activity. The most severely affected abalone were those anaesthetised and moved, followed by those that were anaesthetised but not moved. Abalone manually detached without anaesthesia showed non-significant change in most of the parameters. Recovery back to baseline levels occurred within 1 day for most parameters, but not for the neutral red retention times. The experiment was then repeated with very similar results. These experiments indicate a practical means to compare on farm the effects that husbandry methods have on the immune system, which in turn will allow for the development of better husbandry procedures to reduce stresses incurred during intensive mariculture.