Improving domestication of P. monodon is listed as the top R&D target within the APFA five-year plan (2007-2012). Improving fertility is listed as a key strategy for improving domestication.
If domesticated P. monodon broodstock can be produced economically at a commercial scale, Australian prawn farmers will be in a position to significantly improve farm yields and profitability through selective breeding. To date, P. monodon breeding programs have used both green-water pond systems and clear water systems for rearing domesticated broodstock; with the different systems having certain advantages and disadvantages. Developing protocols enabling a pond-rearing phase within the broodstock production cycle has potential to greatly reduce costs of broodstock production, allowing more companies to maintain domesticated lines and increase production of domesticated-selected seedstock throughout the industry.
In 2002, an APFA-lead research consortium carried out a series of FRDC-funded projects to establish a traditional family-based selection program largely using pond-rearing. However, throughout 2006 and 2007, problems with reproductive tract development and fertility of the pond-reared males significantly compromised the domesticated stocks within the program. In two successive generations across two different pond environments, the gonadal development and fertility of the pond-reared males was found compromised. This project aims to determine ‘if’ and ‘how’ a pond-rearing phase can play a role in producing commercially-viable numbers of P. monodon broodstock.
Seedstock production of broodstock reared in clear water systems has also consistently been constrained by low egg fertilisation. However, the effect that male fertility is having on egg fertilisation rates in clear water systems is not known. The proposed project aims to develop reliable means to evaluate male fertility, and practical measure/s of male fertility which can be used by industry. Such objective measures of male fertility will enable male constraints to seedstock production to be identified and overcome.
Given the rationale that pond systems are likely the most cost-effective system for large-scale production of Giant Tiger Prawn (Penaeus monodon) broodstock, this project aimed to determine whether pond-rearing poses a significant risk for broodstock production.
The gross reproductive development of males reared in low-density broodstock ponds was found comparable to sibling males reared in controlled-environment tanks. Furthermore, none of the environmental 'stressors' and dietary manipulations examined impacted on male reproductive tract development. Thus, within the boundaries of the parameters tested, we can state that rearing of male broodstock in low-density ponds does not pose inherent risks of gross reproductive tract impairment.
The project also focused on developing an objective measure of 'male fertility' that could be used commercially; and which could be employed within a monitoring regime. None of the simpler assays, which have typically been used as 'proxy' measures of male fertility, were found to correlate with egg fertilisation rates. One assay that was tested, evaluated levels of 'activation' of 'matured sperm' exposed to 'egg water' (EW-AR assay) and this activation correlated with egg fertilisation. Therefore, this provides a reliable measure of male fertility. However, whilst providing an objective measure, this assay is not straightforward to implement commercially; and certainly the applications of this measure are likely restricted. Importantly, an overall approach to long-term monitoring of stocks is suggested; this approach incorporating application of simpler spermatophore/sperm assessments and the EW-AR assay at different points throughout broodstock rearing and at stocking of the hatchery.
During the project, a previously undescribed abnormality termed 'hollow sperm syndrome (HSS)' was observed through histology. Whether the presence/prevalence of such abnormal sperm impacts egg fertilisation rates negatively is not yet known; and further research is thus required to establish its commercial importance