A Guide to Marron Aquaculture

The following information is directed to those persons who want to aquaculture marron as a stand alone enterprise. For others who want to supplement other activities this information is relevant and each person will have to interpret how to modify the suggestions to suit their site and circumstances.

The Name

"Marron" is the French word for water chestnuts and since a comparison can be made with the colour, shape and taste of the tail to that of water chestnuts it is possible that this is how the name was derived. However, others believe it is derived from an Aboriginal word for 'food' or 'bread'.

History of Marron Aquaculture

Marron only occur naturally in the lower south-west of Western Australia but now can be found from Esperance to Northampton, in other parts of Australia and in many overseas countries.

Marron were grown in farm dams up until the 1960's when some more serious efforts were made to improve their growth and survival. This accumulation of practical knowledge represented the beginning of our industry.

In 1976 an Act was passed to allow the farming of marron under strict conditions. This lead to a slow growth of the industry until by December 1995 the industry was producing approximately 18 tonnes of marketable product per annum from a total of 31 licensed growers.

As a result of submissions put forward by the MGA (in 1995 & 1998), changes made to the legislation have made commercial farming more attractive.

The total production of marron in WA for 1999/2000 was above 42 tonne from approx 250 licences.

Most marketing experts claim that it not worth any top marketeer’s time to deal with less than 100 tonne/annum.

The future of the industry is dependent on the continuation of supplying sufficient high quality product to an expanding local and export market.

The Life Cycle  of Marron

Marron (Cherax tenuimanus) is an ideal species for aquaculture. They grow quickly, grow to large size, have a restricted yet simple reproductive cycle and can tolerate reasonably high stocking densities during culture. Moreover, the percentage of meat to total body weight is equal with the highest for crustacea.

Marron usually mate in late August or early September however on farms in the north of the state this can be advanced by at by at least one month. The warmer the temperature the sooner the mating and hatching. The juveniles are released by mid December. After the marron hatch they moult while they are attached to the mother’s pleopods under her tail. After two months they leave the mother. Some marron mate when they are approximately 18 – 19 months of age, but most marron commence mating in the third spring of their life when they are 30 to 31 months old.

Growth and Production

The growth rate of marron is predominantly dependent on water quality, dissolved oxygen, temperature, food supply, shelter and stock density.

A recent survey by the Department of Fisheries has shown that most farmers achieve a production of less than 600 kg /yr/Ha of growout ponds. 3 Ha of growout ponds require about 1 Ha of broodstock and nursery ponds. However some can get 2+ tonne /yr/Ha of growout ponds when following Fisheries WA recommendations.

If you cannot obtain 1 tonne/yr/Ha of growout ponds, then you are doing many things wrong.

If you achieve 2 tonne/yr/Ha of growout ponds you are doing most things correctly and can aim to do better.

Site selection

You can’t carry out aquaculture without water!!

Suitable Regions/districts

Within Western Australia successful marron farming using present knowledge is likely to be confined to the area south west of a line running from about Geraldton to Esperance.

Ecological history of site

The past use of the land is very important. Many farmers have run into problems associated with the past use of pesticides, and also with heavy metals associated with fertiliser applications

Size of Farm

For a stand alone operation it is likely that one family can manage a marron farm with about 3 Ha of growout ponds which will require a total of about 4 Ha of water and equates to about 10 Ha of land. Those looking for only supplementary income will get by with less.

Slope & Aspect

For a commercial sized operation costs and total land requirements increase rapidly on land which has a slope greater than about 5° ( ie a fall of 5 meters per 100 meters).

Flat ground has many advantages in giving flexibility in management, and these often outweigh the perceived cost of having to pump water rather than let it flow downhill from one pond to another.

The orientation of ponds can have a marked effect on the natural aeration by prevailing winds.

Water requirements

Within the area of potential marron farming the average annual evaporation rate is 1400 to 2800 mm. This equates to 14 – 28 megaliters of water per Ha per year. Note that 100 mm of evaporation or leakage is equivalent to 1 megaliter of water per Ha.

In addition, allowance must be made for leakage or infiltration.

Leakage is directly related to the soil type and amount of compaction carried out at time of construction of ponds. It is irrespective of climate or weather. This can range from 0.2 mm per day ( 73 mm per annum) for well compacted ponds in good soils to 37 mm per day (13505 mm per annum) or even more when the ponds are built in poor or marginal soils and not adequately compacted.

Converting these leakage figures into annual water requirements gives 0.73 and 13.5 megaliters per Ha per annum for the low and high values respectively. Leakage rates of more than about 15 mm per day are likely to have severe effects on the profitability of the farm.

Marron can grow without any reduction in growth rates in water from 170 to 2500 ppm salinity.

The water needs to be free of high levels of base and other metals such as aluminium, ferrous iron, cadmium, zinc etc. The water supply needs to be tested and if required, simple treatment systems can be installed.

Marron evolved in waters which are unusual compared with fresh waters in other parts of the world. The chemistry of the rivers in the south west corner of WA are just dilute seawater in that the dissolved salts are mainly sodium chloride rather than calcium bicarbonate/carbonate which is normal elsewhere in the world.. The same chemistry occurs in our groundwaters on the coastal plains from Geraldton to east of Augusta.

Marron Husbandry Parameters
Oxygen & temperature requirements

All animals need oxygen to live. Marron are no different. However, being aquatic, benthic animals, they get their oxygen from that dissolved in the water. The amount of oxygen that can dissolve in water decreases with increasing temperature and salinity. It also depends on the percentage of oxygen in the air with which the water is in equilibrium.

For optimum growth marron need DO (Dissolved Oxygen) in the water to be above 8 ppm at all times. Values below 6 ppm stress the animal.

The optimum temperature at which marron grow fastest is 24° C. Deaths start to occur above 26° C.

Dissolved Oxygen in  ppm (parts per million)

Feeding

 Marron can survive for weeks without food but don’t expect them to grow.  A well balanced artificial diet for marron has not yet been developed. Consequently  good growth depends on utilising the natural food production in ponds. Recent experiments by DoF WA has shown that ponds which have a good zooplankton and higher invertebrates population supply the essential nutrient factors. The most important thing about feeding is to give enough.

The best advice that can be given at this time is to demand feed at or just after dusk at least 6 days per week and to vary the feed as much as is practical with the lowest cost feed one can obtain. It is not recommended that spoiled feed be used.  It has been clearly demonstrated that light inhibits marron from eating. This is why we recommend feeding at night.

Shelter

Marron spend most of their time just sitting ( and hopefully digesting their food and growing). They like to do this in shelter away from predators and their hungry, cannibalistic,  mates who may attack and eat them.

This is an aspect that is frequently overlooked, even by long time marron farmers, since construction of suitable hides is a bit of a bind.

Hides should be either plastic pipes of suitable length or plastic mesh posies. Old vehicle tyres are not recommended since they get too heavy to move when filled with mud and there is some evidence that they can  leach heavy metals into the water.

Predator control

The main predators in order of effect on profitability are waterbirds (cormorants, heron etc), humans, water rats & tortoises.

Most  farmers who have had problems with waterbirds have doubled to quadrupled production after installing secure netting over their ponds. However, some farms are hardly bothered at all; it is very site specific.

Stock management

Keep broodstock males and females separate until mating time, separate males as soon as possible after mating and females from juveniles as soon as possible after release of young.

Rear juveniles in nursery ponds until about 30 g weight, remove females at about 2 g size so that you can use all male grow out. Grade into size cohorts at intervals of 1 to 4 months to improve growth rates. The longer intervals apply to larger animals. (Recent work on Kangaroo Island throws some doubt on the practice of single sized cohorts.)

Harvesting

There are two main classes of harvesting:

1. Drain Harvesting: drain harvesting completely drains the pond and one gets a large haul all in one go.
2. Trapping (including drop netting): Trapping is spread over a longer period, gives a more even flow of product, but is selective.

Correct harvesting and post harvest practices can have a dramatic effect on the quality of product getting to end consumer and should be planned carefully.    The recently completed Code of Practice for the Harvest and Post Harvest Handling of Live Marron for Food is essential reading here.

Marketing

Nearly all (if not all) market failures have been due to lack of supply.

 Currently almost all marron are sold live to the end user, mostly restaurants etc. However, there have been some successful freezing tests, and a lot of failures.

The total production of marron in WA for 2002/2003 was above 52 tonne. Most marketing experts claim that it not worth any top marketeer’s time to deal with less than 100 tonne/annum.

If one wants to market directly, it is only sensible to ask around and find out what the current  market prices are.  Cooperatives and wholesalers need a minimum of $8 between farm gate prices and wholesale prices to restaurants. Caution is required here and one should remember that with a total current production of under 60 tonne per annum, it should, with patience, be possible to sell all marron at top  prices.

Costs

Capital costs for construction of ponds and associated facilities can vary by a factor of more than 4 without including the cost of land and of course are site specific. Moreover, most farms will  have to wait until year 3 or 4 before any significant income.

A figure of $50-60,000 per hectare is a good first estimate.

Some farms have been constructed at a cost of over $100,000 per Ha. The actual figure is both site and equipment dependant.

Operating costs, on the other hand, can be quite low especially if they are not fixed at an unnecessarily high level by skimping on capital.

The main operating costs can be divided into 6 areas viz.

1. Labour
2. Water
3. Feed
4. Aeration
5. Packaging & Transport.  Maintenance (which is frequently overlooked when doing budgets).
6. Direct operating costs can vary from $6 to $25 per kg depending on size of farm and how it is managed.

At the lowest and highest figures, the farm is not likely to be profitable in respect to use of resources.