EFFECTS OF SEASON, TEMPERATURE CONTROL, BROODSTOCK CONDITIONING PERIOD AND HANDLING ON INCIDENCE OF CONTROLLED AND UNCONTROLLED SPAWNING OF GREENLIP ABALONE (HALIOTIS LAEVIGATA DONOVAN) IN WESTERN AUSTRALIA

Managing the broodstock conditioning process is important to the successful establishment of an abalone industry that can reliably produce juveniles from captive stock and pursue selective breeding. Four conditioning periods of 6, 8, 10 and 12 wk intervals were tested with captive greenlip abalone (Haliotis laevigata), using a constant conditioning temperature and ambient temperature as a control. The conditioning periods of 6, 8, 10 and 12 wks are equivalent to ~420, 560, 700 and 840 EAT (effective accumulative temperature), based on a biological zero point (BZP) of 6.9°C for gonad development. Greenlip abalone broodstock collected from the wild (87.5–142.1 mm in shell length and 108.2–482.8 g in whole weight) were spawned in all seasons including numerous induced spawnings outside of the normal breeding period with conditioned stock. Over the whole trial period, greater egg production from prescheduled spawnings occurred in the conditioned group with an average of 1.70 × 106 eggs per tub of 5 female abalone per planned spawning, compared with abalone held in ambient control tubs that only produced an average of 0.40 × 106 eggs per tub. Animals that were spawned every 8 wks produced the largest average number of eggs per holding tub, however, there was very little difference between conditioning periods in terms of number of successful spawnings per spawning round. The egg production for all planned spawnings was highest before the “natural spawning season” for greenlip abalone. In comparison, the highest numbers of unplanned spawnings occurred around the natural spawning period for the conditioned and control groups. Handling abalone did reduce egg production within the trial, but this was not statistically significant. Histological examination showed that using the visual gonad index is not a good indication of maturation of the abalone and confirmed that abalone can be conditioned out of season.