A gonad conditioning study of the greenlip abalone (Haliotis laevigata)

The Australian greenlip abalone Haliotis laeviqata is of commercial importance in the abalone diving industry. The species is also believed to have culture potential and accordingly control over reproduction is considered valuable. The major purpose of the study was to accelerate gonad development resulting in spawning outside the natural spawning season. Abalone were collected from Franklin sound in the Furneaux group of islands off the north-east tip of Tasmania. The important features of the conditioning tank were elevated water temperature, the provision of water movement within the tank to distribute feed to sedentary abalone and a diet of preferred red algae. Animals collected on 27 April 1990 were induced to spawn on 21 August 1990, 112 days or 1750 degree days following commencement of gonad conditioning. The natural spawning season of the source population was found to be November to March. A variety of methods for measuring reproductive development of abalone were used. This allowed the utility of individual methods to be examined and comparisons made between methods. Two gonad indices, the gonad bulk index (GBI) and the modified gonad bulk index (MGBI) were used as were a number of assessment methods with a histological component: oocyte size/frequency distribution, mean oocyte diameter, an ovarian phase method and percentage mature spermatozoa. The MGBI was considered more sensitive than the GBI, detecting first significant gonad growth following six weeks of gonad conditioning, compared to nine weeks for the GBI. The gonad indices increased from initial values of 14.1 ± 4.4, n=10 and 0.4 ± 0.2, n=10 for GBI and MGBI respectively to 72.3 ± 9.2, n=10 and 7.0 ± 2.0, n=10 following 105 days of gonad conditioning. Mean oocyte diameter (Am) increased from 30.7 ± 2.0, n=5 initially to 109.7 ± 6.0, n=5 during the same time period. The percentage of male germ cells present as mature spermatozoa increased from zero to 90.6 ± 16.3, n=5 following 24 weeks of conditioning.