Our recirculating aquaculture grow-out system (RAS)

We pioneered the use of recirculating aquaculture systems (RAS) to produce Murray cod in the late 1980’s. Today, we have almost 30 years of experience in the recirculating aquaculture of Murray cod, and continue to produce premium quality Murray cod that consistently fetches market prices that are up to 40 per cent higher than the average wholesale price of farmed Murray cod from other producers.

Combined with our knowledge and experience in Murray cod biology and husbandry practices, recirculating aquaculture allows us to have almost complete control over the growth and quality of the fish we produce. Indeed, through our monitoring and recording of water quality and fish health data, recirculating aquaculture has indirectly enabled us to greatly expand our working knowledge of Murray cod biology and improve our husbandry practices.

Our current grow-out systems are larger recirculating aquaculture systems into which the juvenile fish from the nursery are introduced once they become too large for the smaller tanks in the nursery. This event occurs in the weeks prior to the introduction of new season fingerlings into the nursery, between November and January. Once introduced into the larger tanks in the grow-out systems, the juvenile fish have more room to swim and feed, and thus grow more quickly.

As with all indoor systems in our farm, our grow-out systems use pristine bore water to eliminate the possibility of any outside contaminants or diseases being introduced. Our grow-out systems incorporate all of the main subsystems common to modern recirculating aquaculture systems, including drum filters that provide mechanical filtration of suspended solids, biofilters consisting of friendly bacteria that remove waste ammonia, and oxygenators that add fresh oxygen into the systems. Various other subsystems are used for specific fish sizes, but the key principles remain – conservation of water, monitoring and control of water quality, careful management of fish health, and automation of repetitive tasks while allowing for human action where required.

For all of our production systems, we reuse even the small amount of water that is eventually discharged as wastewater. Our discharged wastewater flows into a specialised outdoor drainage pond where it becomes a nutritional source to raise zooplankton and other microbial life that will become the food source for new season fish larvae. Thus, no water is wasted in our recirculating aquaculture systems, no matter whether it is recirculated through the systems or ejected into the drainage pond. Correspondingly, none of the water in our recirculating aquaculture systems are discharged into local river systems, where it could otherwise be a pollutant.

We independently developed our first recirculating aquaculture systems in the 1980’s, when we were the first to demonstrate the feasibility of recirculating aquaculture of Murray cod.

At the time, we had pursued this venture despite the existence of long-standing doubts from the scientific and industrial communities as to its feasibility, mostly due to the aggressive and territorial nature of wild Murray cod.

Since then, we have rebuilt, adapted and refined our existing recirculating aquaculture systems, and built new systems, with the development of new technologies and with our increasing understanding of Murray cod biology and husbandry practices.

Today, our current systems are specially-designed for Murray cod aquaculture, while minimising maintenance requirements, providing superb water quality, and allowing for responsive control over water quality and fish health factors.

At the same time, we have found Murray cod to be a highly-adaptable species that will thrive in aquaculture, including in recirculating aquaculture systems and even in overseas environments, both rural and urban. With the correct parameters and effective maintenance, and water and fish health management, Murray cod can reach market size quickly with few complications.

However, perhaps the greatest advantage of using recirculating aquaculture to raise Murray cod, is that Murray cod grown in well-managed recirculating aquaculture systems will generally have a superior flavour even compared to wild Murray cod. As Murray cod is a fish that closely reflects its environment – especially water quality – wild Murray cod will tend to have what is often referred to as a “muddy” flavour that reflects their diet and behavioural tendencies as a bottom feeder. In contrast, Murray cod that are farmed in sufficiently clean water, such as those raised in well-managed recirculating aquaculture systems, will not exhibit these “muddy” qualities in flavour, while still retaining the umami-rich, hearty flavour that is unique to Murray cod.