The use of mains water is generally considered to be uneconomical to operate a large scale recirculating system, so existing SA farms utilise water from bores.
Bores supplying farms provides water at lower temperatures which is then heated by bottled gas or compressed air through a heat exchanger to 27°C which is around the optimum temperature for the culture of barramundi.
General biological water quality requirements for barramundi are as follows:
Fingerlings:
Long term access to broodstock is important and the industry is keen to encourage the development of South Australia’s own broodstock capability.
This would in turn improve the opportunities to farm barramundi within the state and result in an increase in the volume being produced.
There is a single hatchery in South Australia who imports eggs from Queensland which are then hatched and reared to fingerlings.
They are currently developing techniques to spawn broodstock and produce eggs within the hatchery. However fingerling production from this hatchery is presently limited and can not supply all barramundi farms in South Australia.
The remaining fingerlings are bought in from Queensland with disease free certification. The procurement of stock is a major ongoing expense with fingerlings costing about 30 cents each, based on a standard rate of 1 cent/mm.
When fingerlings are placed within nursery tanks upon arrival at the fish farm, stock should be regularly size-graded, thus keeping similarly sized fish together and reducing the incidence of cannibalism and stunting.
Feeding and Growth:
Pelleted products are presently the best source of feed for aquaculture in recirculating systems. Pellet feed is cheap, free of disease, available at short notice, available in a range of sizes and formulations and lasts for long periods without refrigeration.
Several companies produce pellet feed specifically designed for barramundi. Different size feed contain different ingredients; smaller fish require more protein. As the fish grow they will require different sized feeds. SA barramundi farmers use locally produced pellets which contain 45% fish meal and cost $850/tonne.
Fish under 100 grams are fed four times a day, while those larger are fed twice a day, usually at 12 hourly intervals. Whilst the food conversion ratio (FCR) is currently around 1.1:1, FCR’s have ranged from 0.7 to 2.0:1.
Under the optimal conditions, barramundi are able to grow from 30 mm (0.5 grams) to 300 mm (375 grams) in five months. Saleable or ‘plate size’ fish are between 330 grams and 600 grams. Barramundi grow slightly faster in fresh water and do prefer very low light levels, with a slight 24 hour elevation to simulate soft day light. Maintaining good water quality keeps the growth rate high, and helps in the prevention of disease.
Disease Problems:
Some bacterial or fungal diseases are airborne, and may occur in a system whenever water quality is poor or fish have been severely scarred by attempted cannibalism. Others may be introduced to a system through careless management. Introduced diseases such as viruses or parasites pose more of a threat than airborne pathogens. With good equipment proper management and sensible stocking densities, disease problems are minimal.
Barramundi are also susceptible to a nodaviral infection which effects their nervous system and spinal cord. The Nodavirus in barramundi is still poorly understood and questions still remain over whether it can be transmitted from parent to offspring, mode of transmission, longevity of the virus outside the host, transmission to other species and means of clinical detection
. It is therefore extremely important that barramundi are certified free of this virus before they enter South Australia and that barramundi are housed within fully enclosed systems when they reach the state.
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