Keeping Marron in Backyard Pools

In Backyard Pools

Marron, and other Western Australian freshwater crayfish, may be successfully kept in small backyard pools, ranging in size from as small as 1½m. in diameter (plastic wading pools) to larger ponds of the concrete fish pond type. Water depth need not be in excess of 15cm. New concrete pools should be well flushed and weathered before use and the bottom should be covered with coarse sand. Crayfish get tail sores from crawling on bare concrete and development of a good natural food supply depends on having soil or organically enriched sediment on the bottom of a pond. If a normal tap supply is used, the water should be allowed to dechlorinate for a week or so, with aeration upon first filling of a pool. If bore water is used and contains iron in solution, the iron must be allowed to oxidize and precipitate out of solution before the water is added to the pool. Complete changes of pond water are not required, unless the marron are frequently overfed.

The pool should be completely shaded from direct sunlight during the summer to prevent water temperatures exceeding 25°C or so. Aeration of small pools may be provided by several air stones running off a small aquarium type compressor. Aeration may only be necessary when water temperatures are high (usually late afternoon) or in the early morning if green algae are present.

Algae may be in the form of long green strands or as minute green cells giving the water a green soupy appearance. Such an algal "bloom" adds oxygen to the water during daylight hours but rapidly removes oxygen from the water overnight and conditions for marron can be poor before sunrise without aeration devices.

In stocking the pond, male marron are distinguished by having two bluish penes at the base of the most posterior pair of the five pairs of legs. Females have an opening at the base of each of the middle pair of legs. One male can service five or more females.

In the smallest size backyard pool suggested at the beginning of this article, no more than half a dozen legal sized marron can be stocked. Even then some initial fighting may result in deaths, particularly if no shelters are provided.

Crayfish are mainly active during the nighttime and they like to hide during daylight hours in clearwater because in nature there are many predators. The crayfish should be provided with shelter as short lengths of PVC. piping or as islands of small rocks. Even a pond may need to be caged to prevent bird predation, eg by kookaburras.

Mating and spawning of marron occurs in the early springtime as water temperature rises passed 12 degrees Celsius. The so-called "berried" female carries the developing eggs and then early hatched young marron (less than a centimetre long) attached to swimmerets under her tail. The young marron, resembling their parents, will be released from the female in the late springtime. Bunches of rope fibre or onion bag material should be placed in the pond in anticipation of the release of young. When release occurs the young will seek out this shelter and remain in or close to it during early life. Rather than disturb the female to see how spawning is progressing, examination of the weed in late springtime (usually December) will tell whether spawning has finished or not, for the young marron, if present, cling to the fibre bunches when it is pulled of the water. For the very best breeding results, large adult non-spawning crayfish should be kept in a separate pond from the small young. It is possible to maintain a number of small ponds on schedule of growing, cropping and restocking. Females can breed at two years of age, but usually breed for the first time at three years of age.

The worst practice in marron raising is any zealous tendency to overfeed. Excessive feeding will pollute the water, cause deoxygenation, and deaths. Lumps of meat are particularly bad in this respect. All feeds leach nutrients (fertilizers) in water which accumulate, eventually producing toxic algal blooms. However, nutrients can be "stripped" from the water very effectively by planting bankside sedges and similar aquatic plants with roots and leaves in pots in the pond.

Poultry pellets can be fed but require some weeks to break down to a rich bottom layer of detritus. Red worms found in compost or manure heaps are better for a small pond and just a few marron since worms can be eaten immediately and do not pollute the water. These worms can be cultured the year round in a wooden box, kept in a cool place, initially filled with a mixture of pre-soaked cow manure and garden peat moss (1:1). Soaked poultry pellets or kitchen vegetable scraps (non-acid) can be placed on the surface of the mixture occasionally to feed the worms. Larger worms with a "collar" are breeders.

Periodically, each marron will become inactive and tend to remain in its shelter or when moving about appear very sluggish and perhaps its shell will become dirty. This behaviour is normal and the marron should not be handled or interfered with, since it is preparing to cast off its old shell which will allow it to grow in size by expanding a new soft shell underneath (the growth process in crayfish called ecdysis). The empty shell will be seen some time later while the marron will be, after a short period of shell hardening (when again it should not be handled) most active in its shiny new shell and eat more food per day than at any other time.

In an Aquarium

Crayfish can also be kept in an indoor aquarium. The best setup is one which has a "sand-bed filter" on the bottom of the glass tank. This filter is a perforated plastic plate which sits just off the bottom, covered by a layer of fibreglass mesh which supports a layer of fine gravel covered by coarse sand. The plate has one or more air lift tubes and a small air blower provides a stream of air bubbles up the tubes to pump and circulate the tank water through the sand bed. All this filter and air equipment can be found in an aquarium fish shop. The sand bed provides a good foraging sediment for crayfish. Several small crayfish can be maintained for many months with careful feeding to avoid overloading this mini ecosystem with nutrients. Earthworms are a safe feed.