In the past, hatcheries producing the Sydney Rock Oyster (SRO) have had challenges with specific production aspects, impacting hatchery operation costs, production reliability and supply of SRO seed to market. The hatchery sector for SRO is still in its infancy and any improvements in reliability will significantly improve the prospects for its continued development.
Scientists have been given CRC-P funding to work on a number of areas with industry to improve SRO hatchery production, such as: tetraploid technologies (Southern Cross Shellfish), increasing viable gamete storage times (The University of Newcastle), understanding spawn-inducing factors and improving maturation protocols (University of the Sunshine Coast - USC).
TETRAPLOID SRO – SOUTHERN CROSS SHELLFISH
Tetraploid SRO broodstock enable reliable and straightforward production of triploid batches which have 3 sets of chromosomes as compared to traditional diploid oysters, which have 2 sets of chromosomes. The extra set of chromosomes result in functionally sterile oysters that grow up to 30% faster than a standard diploid. Triploid oysters also provide oyster farmers an opportunity to sell triploids when diploid oysters are not suitable for marketing due to their lower meat quality.
Many NSW farmers have eagerly awaited the option of being able to stock triploid SROs on their farms. Supply has been hampered by outdated harmful chemical induction techniques which produce batches with low triploid percentages (approximately 80-85%).
A far more effective method for triploid production has been proposed, involving the use tetraploid (4N) stocks. Attempts were made over a decade ago to produce 4N SRO using the Pacific oyster technology, but were unsuccessful. This technology has been refined significantly over the years and has been very successful for Pacific oyster triploid production.
Currently, creating SRO tetraploids continues to be a challenge for this project. Further attempts to induce tetraploids were performed by Southern Cross Shellfish in February 2019. About 150 to 200 spat were settled from recent induction attempts which will undergo analysis to determine their chromosome amount (as known as ploidy analysis) when they reach a larger size.
GAMETE PRESERVATION – UNIVERSITY OF NEWCASTLE
Previous work with the University of Newcastle (UoN) has focused on the development of techniques to better understand SRO gamete viability. Strip spawning techniques are used to obtain gametes for SRO breeding runs which requires broodstock to be sacrificed. The success rate of SRO single-pair mated crosses is often around 25% which means that large numbers of valuable and limited broodstock are used for breeding runs. Failed batches can be identified by hatchery personnel 24 hours after fertilisation. It usually takes about 10 days of strip spawning’s to get the number of families required for a breeding run.
The capacity to simply and cheaply store gametes for short periods of time during breeding runs offers a number of advantages for SRO breeding. Oysters that are sacrificed and are not immediately mated can be stored and be available for crosses in the latter stages of strip spawning’s. When larval batches at 24 hours post fertilisation fail, stored gametes can be used to quickly create additional families. This allows more effort to be devoted to assessing broodstock and structuring crosses to meet the objectives of the breeding run.
UoN is investigating protein profiles to extend the storage of SRO gametes. UoN conducted an experiment where SRO were conditioned and then held in different environments (low temperature and standard temperature). Flow cytometry is being used to analyse and optimise staining of gametes to ensure their methods are accurate and the literature is being reviewed for other potential methods for the extended storage of gametes.
MATURATION AND SPAWNING - UNIVERSITY OF THE SUNSHINE COAST
Having ripe, ready-to-spawn broodstock that readily release gametes is both a challenge and a significant financial impost for SRO hatcheries. SRO broodstock can take up to 10 weeks to bring into condition within a hatchery and can consume up to 80% of the algae required for a hatchery production run - this is both time consuming and expensive.
In addition, natural spawning of SRO is uncontrollable and the processes used to stimulate spawning require physical stresses (e.g., salinity and thermal shock) can also be impractical. The alternative is strip spawning from ripe, mature broodstock to harvest gametes for fertilization, although this technique gives a low fertilization success rate when compared to natural spawning. Identification of an SRO natural spawning inducer would be most helpful to allow for high fertilization success.
The University of the Sunshine Coast have been investigating the expression of gametogenesis-related genes, at 7- and 14-days post-treatment with various reproductive neuropeptides. SRO spawn inducers have been identified in the form of sperm-associated proteins, which are effective on both males and females. Acceleration of reproductive condition stimulates spawning on demand and could significantly reduce hatchery costs.
For more information on this project, please visit: https://www.oystersaustralia.org/project-2016-803
The author acknowledges that the CRC Program supports industry-led collaboration between industry, researchers and the community. The Future Oysters CRC-P, which focuses on the production of ‘Better’, ‘Healthy’ and ‘More’ oysters, is led by Australian Seafood Industry Pty Ltd in partnership with Oyster Australia Ltd, Select Oyster Company Pty Ltd, Fisheries Research and Development Corporation, Department of Primary Industries and Regions (South Australian Research & Development Institute), University of Tasmania, The Flinders University of South Australia, The University of Newcastle, The University of Adelaide, Commonwealth Scientific and Industrial Research Organisation, University of Technology Sydney, University of Sunshine Coast, Macquarie University, Department of Skills and Regional Development (NSW), and The Yield Technology Solutions Pty Ltd.