Development of a spermatogonial germ cell transplantation platform for southern bluefin tuna (Thunnus maccoyii)

Germ cell transplantation technology may become an important tool for the successful closed life-cycle aquaculture of southern bluefin tuna (Thunnus maccoyii) (SBT), to ease the fishing pressure on the wild stocks and develop a self-sustained industry. Currently, there are issues surrounding the care and maintenance of SBT broodstock, as they are large animals (up to 160kg) and reach sexual maturity at a late age (10 – 12 years). Germ cell transplantation has the potential to overcome the difficulties in maintaining large bodied broodstock, such as SBT, by transplanting donor-derived testicular cells (SBT) into a smaller bodied surrogate species such as yellowtail kingfish (Seriola lalandi) (YTK). YTK has been selected as a prospective surrogate host, as YTK larval development and spawning occurs at a similar temperature as SBT, and reaches sexual maturity at a younger size (3kg) and age (3-4 years) than SBT. Another reason why YTK has been selected as a potential surrogate for SBT is that they are a commercially important species and the aquaculture of this species is already well developed in South Australia, in close proximity to where SBT testis material is available. The current study has laid the framework for a germ cell transplantation protocol for SBT by establishing some of the prerequisite knowledge required for this technology to progress. The first component of the study optimised an effective protocol to collect and dissociate SBT testis material to obtain a high number of viable testicular cells for transplantation was developed. This component also examined the effect of size and maturity of SBT on obtaining viable cell numbers. Secondly, the study confirmed an effective method to cryopreserve SBT testis material to ensure that SBT testicular cells were readily available year-round for germ cell transplantation. The study established the optimised rearing conditions for YTK in a small-scale rearing system in the third component. Lastly, the current study assessed the suitability of YTK as a surrogate host for SBT by successfully transplanting SBT testicular cells into YTK larvae, and then rear those transplanted larvae at low density in a small-scale system. This component successfully demonstrated that YTK supported the migration and colonisation of transplanted SBT testicular cells and therefore, YTK has the potential to act as a surrogate broodstock for SBT.Submitted in the fulfilment of the requirements of the degree of Master of Science, Univesity of the Sunshine Coast, 2014