The Australian prawn industry needs a mechanism by which to confer genetic protection of seedstock with elite genotypes so that their commercial benefits can be made available to the entire domestic industry through the sale of elite seedstock for on-growing. To-date triploidy is the only available technology that is near commercialisation that provides a high level of genetic protection through reproductive sterility.
Triploidy has the added benefit of resulting in female populations, with females naturally growing larger than males. This attribute should provide further improvements on harvest yield beyond the performance provided from the elite genotypes alone. If this project demonstrates that total harvest yields are substantially improved through stocking triploids as predicted, triploid induction technologies will be of direct benefit to (and can be utilised by) the entire Australian industry as wild spawned females are also larger than males. This provides direct benefits to the industry independent of accessing the elite genotypes being produced by the four largest Australian prawn producers, providing immediate benefits for any Australian farm or hatchery producing seedstock.
Final report
Several Australian companies currently have breeding programs producing domesticated and selective-bred Penaeus monodon lines. The most advanced of these lines have demonstrated high commercial pond performance over several generations. However, there is a risk for the breeding program companies, due to on-sale or on-rearing of their selected postlarvae. To avoid this problem, genetic protection for the selectively bred prawns is required; however, to-date there is no commercial method for fail-proof genetic protection of prawns. Triploid induction is the only methodology that has been trialled experimentally that shows promise of genetic protection in prawns. However, there are limited reports of triploid induction in Black Tiger Prawns and no studies have reared the larvae through to harvest age and conducted rigorous performance measurements for this species.
This project aimed to develop a technique that would be suitable for commercial triploid induction (which gives each individual an extra set of their own chromosomes; a process that occurs sporadically in nature) of whole spawnings of the Giant Tiger Prawn. A methodology was developed to induce whole spawn triploidy with temperature and chemical shocks. However, hatch rates from this system were consistently low. Despite this a chemical induced triploid family with a high induction rate and reasonable larval survival was produced at a commercial hatchery, allowing rigorous tank-based performance assessments to be carried out.
The overall performance of triploids was comparable to other penaeid prawn species with some exceptions. In triploids, survival was lower, and females were significantly larger. Furthermore, there were more males than females with a 1:1.625 sex ratio and reproductive age triploids were unable to produce viable offspring. This demonstrates that triploidy would provide the industry with a method of genetic protection for Black Tiger Prawns, however significant challenges in maintaining high hatch rates, survival rates and induction rates of the triploids when inducing whole spawnings on a commercial scale still remain.
