When Alan Steel and John Thompson took a stake in the Australian Blue Yabby Aquaculture (profiled in Austasia Aquaculture Vol 16-5) two years ago, little did they realize they would become the owners of yabby technology that carries world wide patents and the potential to revolutionize how freshwater crayfish are produced.
Over the last 12 months, working from their Thomastown Melbourne factory, they have taken the technology to much higher levels and then refined it. The system is now ready for commercial development. The major improvements came in the feeding techniques, both the diet and the delivery. Other improvements were in the filtering system, tank design and the actual ‘capsules in which the yabbies are housed.
Control over production:
The primary attraction of the system is that you have total control over production and inputs. Yabby farming has been plagued with many recurring limiting factors, seemingly more so, than other aquaculture sectors. Appropriate dietary regimes, attrition (especially during moulting) and, the murkiest of all, predation have all played a part in making the industry a hit and miss enterprise.
The market availability of product has also been dictated by the weather. The cost to the animal’s market image has suffered accordingly. Farmed trout, mussels, salmon, oysters and prawns are all found in the supermarkets. Yabbies are seen as a novelty item bought through speciality outlets — and then only “in season”.
Every grower has a personal tale of getting a crop of yabbies close to market size only to have the ponds beset by birds. Tortoises are another persistent and under-rated predator. In eastern coastal regions, eels have invaded ponds and water rats seem to find ponds in the most remote places.
This led to one of two strategies for the industry. Either invest in costly predator control or gamble on getting away without it. The interesting thing is that everyone can quantify the cost of predator control but no one seems to be able to quantify the cost of not having it. One of the hidden costs of not having it is that growers lose control of the management of their production systems as biomass calculations fly out the window.
This makes feeding rates and marketing a guessing game. Inability to manage production methods has left the sector in limbo between an opportunity crop and a genuine industry, as the current state of the industry nationwide reflects.
By growing them indoors, ABYA immediately eliminate one of yabby farming’s biggest bugbears. As Alan, an accountant by profession, points out “it also provides maximum control over environmental factors, water temperatures and quality, 24 hours a day all year round.” In effect you get the steak knives thrown in with the predator control.
Apart from the security and environmental issues, there’s the bio-security aspect. This works both ways. The water in the tanks at ABYA is the same water they started with 30 months ago. Environmental impact is minimal and yabbies can be grown outside their natural range without threat of escape. From a marketing point of view they can be grown close to the point of sale, minimizing transport costs, enhancing freshness and with control over production. Marketing targets can be set and deadlines met.
Principle:
The pilot stage of the system consists of a 5,000L tank in which posts are suspended vertically in the water column. Attached horizontally to the posts are slotted Perspex capsules called cells.
Each cell holds a single yabby. As the water flows around the tank, the cells drift with the water column and collect, through their slots, the slowly sinking feed. The yabbies eat the food that collects in the cells. Waste is expelled naturally from the cells by the water flow and the water is treated by a biofiltration system attached to the tank. Moult shells are eaten and recycled by the yabby in the cell. Although the principle sounds too simple to be true„ behind that simplicity lies years of trial and error.
“Since we’ve been working with the unit we’ve introduced many changes,” says John. “We’ve gone through a huge testing period of feed and feeding methods — when to feed them, how to feed them and what to feed them. But it’s more than that. The cell design, tank design, filtering system and water flows and velocity have all undergone re-figuration to achieve the desired outcomes.”
Nutrition:
The feed is an extruded proprietary crustacean crumble that is slow sinking and fine enough to enter the cells while, at the same time, getting the yabbies to grow and moult. Slowly sinking feed ensures that the cells all collect, roughly, an equal amount of the food. This doesn’t occur by accident. Much trial and error went into getting the water flow and velocity just right and finding the right food.
While growth rates vary, it doesn’t appear to be related to the level on which the particular cell sits on the post. How the feed reacts with the water and its sinking rate are key elements in the efficiency of the system. Whilst Alan and John are discussing with the manufacturer some minor changes, on the whole they feel they have the diet that will make the yabbies’ grow. Alan says they trialed seven or eight different feeds until they got it right, both in terms of delivery and growth.
The system:
The pilot system’s filtration medium is a cartwheel-shaped inert plastic bead. Two sizes are used. The first line of filtration is by the smaller, l cm size bead which removes the heavy solids. The second, larger 1.5cm size gives the water a final polish in an upwelling filter. Both sections of the filter nitrify ammonia. Water turnover is a healthy three times an hour.
The water in the tank passes through a settlement box. Because of the inefficient food in use when John and Alan inherited the system, the original system used a 300pm in-line screen as the primary solid removal process. Since they’ve improved the feed and the delivery system, this screen has become superfluous.
However they have left it in place to prove to themselves they are on the right track. The removed solids are bled off the sump once a week. Water exchange is less than 1% a day. Alan, always the accountant, says the bled off solid organic matter could be recovered easily and be sold as fertilizer.
Each 5,000L tank will physically handle 1,200 to 1,400 cells with each post having 14 cells attached to it. The number of cells used at any one time depends on the size of the yabbies being grown. the total biomass being the limiting factor. Alan says that while the pilot only has one tank per filtration system, the commercial models could be supplied with a larger filter servicing two tanks.
The yabbies are fed once every three days. The feed will last in the cells for two days and the third day ensures the water quality is kept within safe water quality parameters.
Aeration is provided by airpumps in the filter and directly into the tank. Not only does this maintain DO levels but also keeps the feed in suspension so that it is all eventually collected by the cells as they rotate around the tank. The filtering system is bypassed during the feeding to allow the cells to strip the feed from the water column. Water is kept at a constant temperature by either an inline heater and/or an atmosphere-controlled room. DO levels are generally around 8mg/L, just a whisker below the saturation level of 8.5mg/L.
Auxiliary crop:
The tank also presently holds 50 goldfish. This quantity will be experimented on in the next few months to optimise this auxiliary crop. They help clean the cells and keep the tank bottom clean as well as provide a secondary cash flow. Introduced at 50mm and they grow to 10-15cm in approximately three months. John says the money you can make from the goldfish helps cover the operating costs of the system. By coming to the surface they also warn of low DO situations.
Author:
John Mosig
