The Australian freshwater crayfish sector has been ‘promising’ to reach mainstream levels of production for decades. Of the three species farmed, yabbies (Cherax destructor), marron (C. tenuimanus) and redclaw (C. quadricarinatus), it is the tropical redclaw that has shown the most promise.
That promise is being revealed by a few dedicated growers in Far North Queensland. Working with researchers led by Dr. Dean Jerry at the Townsville Campus of James Cook University (JCU), they have removed some of the road-blocks that have held this hardy crustacean back from its true potential.
John Stevenson, President of the Queensland Crayfish Farmers Association Inc (QCFA), has been farming redclaw since 1993 and is confident that knowledge acquired from the five-year scientific program will revitalize the industry. Speaking at a Redclaw Revolution Conference held in Cairns he said, “The redclaw crayfish industry is on the verge of emerging from its fledgling state and entering maturity. The stage is set to adapt the experience and technology that has been gained to large-scale farms. Redclaw farming can be sized to be a stand-alone operation or be integrated with other agricultural or pastoral pursuits.”
The major game-changer has been the new “S3J” method of farming: This entails stocking production ponds with common-age juveniles raised in a climate-controlled hatchery. The name comes from the growth stage – Stage-3-juveniles – when they leave their mother’s pleopods and become free-swimming organisms. At this point – 10 days after hatching when they weigh about 0.02g – the juveniles are stocked into freshly flooded ponds.
Development of the first hatchery began in 2006 at Col and Ursula Valverde’s ‘Aquaverde Redclaw’ farm, which is now in full production. A second hatchery was built in 2007 to service the Selective Breeding Project at Ross and Wendy Martin’s farm and was supported with a $130,000 grant from the Australian government’s Rural Industries Research & Development Corporation (RIRDC). Stevenson noted that this was essential to establishing the new approach. This hatchery is now being rebuilt to suit commercial production. Both hatcheries are situated on the Atherton Tablelands, inland from Cairns.
Selective Breeding Project
The development of hatchery technology for the Selective Breeding Project was a co-operative effort between QCFA and the Aquaculture Genetics section of James Cook University. It has enabled the QCFA to produce commercial numbers of S3Js economically.
Initially broodstock were selected from the eight participating farms – their best 170 females and 70 of their best performing males. As all the farms had been breeding from their own stock for at least fives years, these cohorts were considered to be relative homogenous and made up the first eight family lines. The ninth family line was provided by the QDPI research station at Walkamin. This was a line of redclaw developed when the station was investigating crayfish performance. Two others came from stock collected from three catchment areas.
The make-up of the wild stock incorporated into the program to infuse genetic diversity is interesting. Trapping in one system provided sufficient stock to establish a breeding team, however, there was such a gender imbalance among crayfish from the other two systems that the males from one were teamed with the females of the other. In all, the selective breeding program started with 11 family lines.
The spawning program was designed to be circular: males from Family 1 were bred with females from Family 2; Family 2 males with Family 3 females, etc. The next year Family 1 males were joined to Family 3 females; Family 2 males to Family 4 females… and so on.
This created 11 new families each year. Ten thousand from each family were sent to participating farms where they were reared for eight months at which point 170 of the best females and 70 of the best males were selected to make up the breeding teams for the next season. These new families replaced the old families and became the founders of the next. The old families were not bred again.
Breeding for the farms
Crayfish are stocked in the spawning tanks at one male to three females. Conditioning redclaw feed comfortably on pellets or soy bean at 20°C and will build up their reserves until stimulated into spawning by raising the temperature and increasing day-length. So, as warmth returns to the ponds the water temperature is increased from 20°C to 25°C over seven days and the artificial daylight in the spawning room is lengthened. This triggers spawning. Once the spawning cycle is complete and the eggs have hardened they’re stripped into incubators designed along the lines of the Finnish Heputin model. They hatch 200,000 juvenile crayfish per sitting. This critical mass provides an information base large enough to draw meaningful data upon which to plan the selective breeding program.
Incubation takes 3-4 weeks. The juveniles live on their yolk sack for 10-14 days during which time they become fully formed juvenile crayfish, ready to be stocked in the growout ponds. The whole cycle takes 4-6 weeks. The juveniles are transported from hatchery to farm in plastic, oxygen-filled bags.
As with many breeding programs, the benefit was not singular. The most significant gain came from conditioning the spawners indoors. Stevenson noted there was still some fine-tuning needed to enable year-round breeding. But, by manipulating temperature and light, juveniles are available earlier, and they have advanced stocking time by several months – particularly in the south. One Gympie grower relying on natural spawning in his breeding ponds had to wait till Christmas for juveniles to be produced. Now he stocks in late August or early September and starts to harvest the next April.
Growth rates have improved
The gains have been significant. By the third year of the program the average size of S3J redclaw harvested on the eleven participating farms was double that achieved in 2004 at the Walkamin research station. Overall, the program has increased the average size at harvest and the yield per hectare.
The usual size of a pond is 0.1ha (1,000m2) and an average harvest after eight months from such a pond is 300kg. They have eliminated the uneconomical segment of the catch that would normally have to be carried over to the following spring, and the average size has been lifted into a higher value price bracket. However, there’s still a size range among the harvested crayfish; large ones can weigh in at 400g after 8-months growth.
The biggest advantage has been in the changes to farm programming. By being able to condition and spawn crayfish out of season, growers are able to stock their ponds as soon as the water warms up, rather than waiting for the natural breeding season to begin. This extends the growing season by as much as 8-10 weeks. Ponds hitherto used for breeding, or set aside to grow out stragglers are now fully productive.
Ponds stocked at a known density with common-age juveniles give a management starting point: the biomass is calculable at any time. This allows growers to manage and monitor feeding regimes using a species-specific diet based on the nutritional needs of the animal.
Stevenson noted that growers in southern areas probably gain the most from buying hatchery-spawned juveniles. Rather than waiting for natural spawning to get underway, they can stock with S3Js as soon as their ponds reach optimum temperature. They can now grow a crop in one summer, avoid winter attrition and unwanted natural recruitment. They now get three crops in three years where they were previously getting only two.
Serendipity played a role
Probably the most significant gain has come serendipitously. The JCU team identified a number of bacterial strains that are ubiquitous in crayfish ponds. In the past, with ponds being under water for consecutive seasons, sometimes for three or more years, the bacterial loads could reach epidemic proportions. Now, with regular drying-out and liming of the ponds, that bacterial cycle is broken. Furthermore, by stocking with common-age juveniles that are quarantined in the hatchery, no bacteria are introduced with the seedstock.
Ironically, there is a bacterium that can give them grief in the hatchery: Aeromonas hydrophila. Initially it caused problems in incubators where survival was either 100% or zero. However, a PhD student made the breakthrough: now regular scrubbing with a 10% solution of hydrochloric acid keeps the essential equipment sterile.
Nutrition is important
Buoyed by the success of the Selective Breeding Project, the QCFA has embarked on a RIRDC-funded feeding and nutrition research program. Stage one addressed the stability of feed pellets in water, the ontogenetic requirement regarding pellet size, and the optimum feeding interval. “The results achieved were astounding,” Stevenson said. “Pellet water stability was increased around fivefold.” Videos of redclaw eating pellets of different sizes showed that matching pellet size to the redclaw being fed resulted in practically no waste: good for both the budget and water quality.
However, Stevenson was most bullish about the markets. A consistent supply of quality product would allow them to explore export- as well as local markets. Adopting the “S3J farming” has the potential to revolutionize the redclaw industry, and will be responsible for the industry’s future success.
Red 14 Breeding compartments (oyster purses) are suspended by cable across the pond. Each holds 3 females and one male. Once in berry, the females are taken to the hatchery and the eggs stripped into the incubators. The compartments are then re-stocked with fresh selected breeding teams.
Red 09 Oyster purses have proven to be cheap and efficient breeding cages.
Red 15 John Stevenson working the winch that lowers and raises the breeding compartments.
Red 11 Stripping eggs into perforated egg-cups.
Red 04 The incubator. Note the return water storage which also acts as a bio-filter tray.
Red 02 The incubator will hold 500 egg cups and produce up to 200,000 S3Js per sitting.
Just hatched.jpg Newly hatched larvae in their egg-cup
final product.jpg About 400 S3J crayfish ready for release into a growout pond
Flow-trapping: how crayfish behavior helps redclaw farmers
Flow trapping was developed in the Queensland redclaw (Cherax quadricarinatus) industry and plays on the redclaw’s natural instinct to move upstream into the flowing water a billabong or creek receives after a dry spell. To survive dry periods, crayfish burrow into the substrate and cap their burrows when the water level falls below the entrance. When the water returns they head for the inflowing water channel. Flow trapping exploits this impulse.
Lowering the growout pond water level to a third or less and setting up a ramp down which the refill water flows stimulates this upstream migratory behaviour and induces the crayfish to ‘walk the plank’ to the lip of a collection bin into which the crayfish fall. This is done at night, so all the grower has to do the next morning is dismantle the trap and take the captured redclaw back to the packing shed for grading.
The advantages are twofold. Apart from the obvious one of having the animals harvest themselves, the ‘Pied Piper’ factor ensures that the pond is harvested totally. This eliminates self-recruitment in the pond when it is flooded again and stocked with common-age juveniles. If not harvested completely pond management becomes a nightmare with crayfish from three cohorts – the ‘stowaways’ and their offspring plus common-age juveniles stocked by the farmer – all cohabiting the pond. Stocking densities become a wild guess, feeding rates become meaningless, and market projections a stab in the dark.
Without flow trapping, the S3J method of farming freshwater crayfish would be seriously compromised.
Red 06 A typical redclaw pond. The tires provide protection from aerial predators such as cormorants, and increases ‘bio-space.’ The fencing keeps out water rats and the low fencing between the ponds prevents migration of crayfish from pond to pond. A flow trap is in the centre.
Red 08 A typical harvest eight months after stocking with S3Js.