Gavin Partridge

The results of this study show that hatchery-reared Black Bream can be used to enhance the stock of the population of this commercially and recreationally important species in the Blackwood River Estuary in which it has become depleted. An initial trial of different stains demonstrated that alizarin complexone was particularly effective for staining the otoliths (ear bones) of Black Bream. The mark on the otoliths, produced by this stain following immersion of hatchery-reared juveniles, was still visible to the naked eye 3.5 years later. Substantial numbers of the stocked Black Bream, which were introduced into the Blackwood River Estuary, were still living at the end of 3.5 years. On average, these individuals did not grow as rapidly as those in the wild population, and unlike the wild fish, not all stocked Black Bream attained maturity by 4 years of age. However, they still grew at a rate that was greater than that in some other estuaries and many did reach maturity by 4 years of age. The Black Bream is thus a particularly good candidate for restocking an estuary as it completes its life cycle within these systems in south-western Australia and consequently any stocked fish are unlikely to move into other estuaries in this region. The ease and relatively low cost of culture of Black Bream and its hardiness and restriction to its natal estuary make the restocking of Black Bream a feasible and economically-viable proposition. This study shows that restocking provides managers with a further and viable option for countering the effects of a decline in a stock of Black Bream in an estuary.

The results of this project will contribute to the on-going development and success of inland black bream recreational fisheries and the inland saline aquaculture industry in general. Several commercial black bream fish-out ventures are now operational in inland Western Australia, one of which utilises saline groundwater. It has been proposed that a pilot project to stock the saline pools of the upper Avon River, which is located in the heart of the W.A. Wheatbelt, should be undertaken to provide recreational fishing opportunities for the inhabitants of a number of rural towns. The continued development of the W.A. inland saline aquaculture industry will result in social and economic benefits to rural areas through increased tourism and opportunities for farm diversification.