Water Supply:
Before commencing any aquaculture venture, a suitable and plentiful water supply is required. Marron growers throughout South Australia obtain their water from a number of sources.
These sources include soaks (where water seeps into a pond or channel from the water table), artesian bore water or run-off from the water catchment.
It is however not recommended that ponds or dams are built directly into the water table and applications for marron farming permits using this method are usually rejected.
As South Australia is the driest state in the driest continent, water is an extremely important resource in marron aquaculture and must be effectively managed.
The majority of marron growers recycle their water into storage dams when draining their ponds to harvest or clean so that it can be used again in the same or a different pond.
It is also advised that if a grower is to rely on run-off water from a catchment area, they should construct a number of dams to store water to ensure that marron ponds can be topped up during the summer months when water evaporation is at its peak.
Aeration:
Artificial pond aeration is used to help maintain oxygen levels in the water throughout the day by aerating and circulating water throughout the pond. Aeration is usually required when ponds are stocked at higher densities and when supplementary feeding occurs. The majority of growers aerate only when oxygen demand within the ponds is high which is usually around dawn and midday.
Mechanical aeration can be achieved using a number of methods. The most popular method in South Australia is using an air-lift pump system which is effective and relatively cheap to construct.
There are also a variety of other methods which can be used to effectively to aerate ponds and include paddle wheels, aspirators or even an outboard motor on the back of a boat!
Pond Design:
Marron ponds are usually constructed on relatively flat or slightly sloping land that allows for water to be supplied or drained to or from the ponds via gravitation. Grow-out ponds are usually rectangular in shape and range anywhere between 500m2 to 5000m2 .
Some growers have indicated that a pond size between 1000m2 and 2000m2 are easier and can be more effectively managed. Grow-out ponds are usually around 1 to 2 metres deep.
Other factors which aid in pond management include
- A definite deep and shallow end to aid in water drainage.
- A sump (well defined low point) in the deep end to aid in pond drainage and crayfish collection during a harvest.
- A central channel down the middle of the pond to aid in water drainage and the collection of wastes.
- Sloping sides to allow for the gravitation of waste products toward the channel of the pond and to allow for the marron to locate themselves at an appropriate depth to suit water quality conditions during that time.
- Drainage and overflow systems
It is advised that ponds are built in “blocks” which reduces building costs, area of used land and the costs of associated infrastructure such as water piping, aeration and netting. Ponds should be relatively close together for ease of management but far enough apart to allow for a vehicle to pass between them which aids in transport for feeding and harvesting.
Diet:
Marron are described as opportunistic feeders which means that they will consume any food that is readily available within the pond system. This includes;
- Plant material – aquatic plants, flooded crops, lucerne, phytoplankton (tiny algae cells) and algae. As marron are unable to digest cellulose they are not able to obtain sufficient minerals and nutrients from eating these products. However many plants provide a medium for aquatic animals to colonise which in turn provides food for marron
- Animal material – aquatic insects and zooplankton (tiny aquatic organisms). This includes free swimming animals as well as animals (alive and dead) inhabiting the pond floor. Animal material provides a good source of protein in the marron’s diet. Zooplankton blooms are usually induced by generating a phytoplankton bloom which results after fertilising a pond with measured doses of fertiliser.
- Detritus – decomposing plant matter which is colonised by bacteria and fungi. Detritus is thought to be a major component of the marron’s diet and is a good source of protein.
As well as the natural food available in the grow-out pond, marron growers also provide supplementary feed. The most common type of feed used in the South Australian marron industry is lupins, a type of legume. Lupins provide a high source of protein and are relatively inexpensive.
Some marron growers also use other feed or supplement lupins with grains such as wheat and barley, lucerne, vegetable scraps, grass clippings and processed crayfish pellets manufactured by a feed company.
Marron are currently fed around twice per week during the summer months which tapers down to around once per fortnight during winter when the activity of the marron slows down. The amount of feed marron are given is around 3% of their body weight per day however most marron growers determine the amount of feed according to the proportion of previous feed which is left over.
It is important not to overfeed as this can result in oxygen depletion problems within the ponds when uneaten food decomposes. Little is known about the nutritional requirements of marron. The above information is based on previous observations but there is still a lot to discover.
For example it is not completely known how important the natural pond flora and fauna is on the nutritional component of the marron’s diet. The relative importance has been speculated by previous studies showing that crayfish fed the best processed pellet diet in tanks do not achieve the same growth rates as marron grown in earthen ponds.
More research is required to investigate into the nutritional requirements of the marron and the role of plant and animal matter, detritus and processed pellets in providing those requirements.
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