The sex of marron can be determined very easily by examining the underside of the marron.
Female marron have oviducts which are located at the base of the second pair (from the head) of walking legs and males have male genital papillae located on the base of the fourth pair of walking legs.
Marron reach sexual maturity after one year of age.
Marron only breed once per year in early spring. Spawning is stimulated by changes in light and temperature. Mature females can produce from 100 to 900 eggs per brood depending on her size with larger females producing a greater number of eggs.
The male deposits a spermatophore within the vicinity of the female’s oviducts where her eggs are produced.
The female then releases her eggs, mixes them with the male’s sperm and attaches them to her swimmerets (pleopods) located underneath her tail. The eggs are then incubated underneath the tail of the female. After hatching, the juveniles pass through three distinct stages before they become completely independent from their mother.
The eggs and larvae are incubated for a period of 12 to 16 weeks and will depend on the temperature of the surrounding water.
Prejuvenile stages of development:
- A Attachment of egg to pleopod
- B First stage of young showing domed carapace
- C Second stage of young
- D Hooked tip of thrid and fourth walking legs of first, second and third stage young used to grip the pleopods of their mother
Supply of Juveniles:
Stocking of juveniles in grow-out ponds can be achieved using a number of methods. These include
- Stocking the pond with a parent population of marron and allowing the natural population dynamics to occur. This method is very extensive and can result in overcrowding and decreased growth rates if the pond is not regularly trapped to remove the large individuals.
- Stocking the ponds with brood-stock marron at a ratio of one male to three females, allowing them to breed and then trapping out the adults.
- Stocking the ponds with berried females however the handling of berried females can sometimes result in the loss of eggs from underneath her tail.
- Breeding the marron within a smaller pond or tank, harvesting the juveniles and then re-stocking them in a separate grow-out pond. This method can be very time consuming and can also result in a loss of juveniles due to handling stress.
Growth Rates and Survival:
Marron grow via a series of moults which involves a period of no growth (known as the intermoult period) followed by rapid increase in size after moulting. Moulting occurs when the entire exoskeleton of the marron is shed to accommodate for a new larger exoskeleton underneath. There are many factors that affects the growth rates and survival of marron. Some of these include
- Water quality conditions
- Stocking rates
- Predation mainly due to cannibalism and birds
- The availability of shelters or hides
- Diet
- Pollutants
Stocking rates within a marron pond usually depend on the initial size of the marron and the extent of pond management (ie aeration, water quality, supplementary feeding, provision of shelter etc).
Growth rates and survival depend heavily on the stocking density of marron. As a general rule juveniles are usually stocked at a rate of 4-8/m2 . More research is required in this area to determine an optimum stocking rate for marron held under various degrees of pond management.
Marron can attain a maximum size of 2.5kg however this is not economically viable due to the costs and time associated in producing a marron of this size. A market size marron between 200g to 250g can usually be attained within two to three years.
Harvesting:
Marron can be harvested using several methods;
- Trapping – baited traps are thrown into the pond during dusk and marron are collected in the morning from the traps
- Drain down #1 – ponds are drained and marron are manually collected. One problem encountered with this method is that marron burrow in response to dropping water levels which can result in no marron being present once the pond is empty.
- Drain down #2 – ponds are again completely drained however a cage is placed around the outlet pipe which collects marron has they follow the water from the pond into the sump area and down through the outlet pipe.
After harvesting is completed, marron are graded into various size classes and then purged in cold water to remove the gut contents. Marron are then packed in styrene foam containers ready for transporting to the market.
Marketing:
Presently marron are marketed anywhere between 200g and 250g. Marron are sold live to various markets both domestically and interstate (mainly Sydney and Melbourne). At this stage production of marron is not sufficient to support an international export market however there is an interest overseas for our marron once production increases. Currently marron are selling at a farm gate price of around $20/kg.
Marketing can be accomplished either individually or through a marketing co-op. The advantages of marketing through a co-op are;
- Consistency of the quality of the product
- Consistency of supply of product
- Stability of the price of the product
- Market advertising is done by the co-op
- Allow even the smallest grower to supply marron to the market
Yabbie co-operatives around the state are licensed to market both marron and yabbies. These Coops was developed in South Australia to ”co-ordinate the orderly marketing of freshwater crayfish grown aquaculturally by registered growers throughout South Australia”. There are three distributions centres located throughout the state in Fleurieu Peninsula, the South East and Eyre Peninsula.
Marron have excellent marketing attributes due to their presentation on the table and substantial meat yield of around 32% of the total body weight. Marron are sold live however there is opportunity for value adding.
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