Farming Abalone

Growout Systems and Feeds

In Australia, abalone are usually grown on land using tanks, troughs or raceway systems (see Freeman, 2001 for drawings of these systems). Additionally, abalone can be reared in barrels or sea cages hanging from buoys or rafts. Ocean ranching (placing juvenile abalone on reefs) has been suggested as an alternative method of culture; however, its economic viability has not been demonstrated in Australia (Shepherd et al., 2000) although enhancement of abalone fisheries with juveniles is conducted on a large scale in Japan (Hahn, 1989). Relevant government departments consider several environmental issues when enhancement of reef with molluscs is proposed (see Lee et al., 2001).

The selection of an appropriate site for land-based, as well as ocean-based, culture of any abalone species is vital to the long term success of the operation (O'Brien, in Foster 1996, pp. 22-27).

Several culture sites in China have had to be abandoned because of excessive silt levels and fluctuating salinity and in general, sites for abalone aquaculture require easy access to seawater of high quality. Specifically, abalone have poor tolerance to the presence of ammonia or nitrite, high or low pH, and low or supersaturation of dissolved oxygen (Harris et al. in Cook et al. 1998, pp. 683-687; Burke et al., 1999). Shallow bays, which periodically accumulate large amounts of decaying seaweeds or overheat, should be avoided.

The behaviour of the individual species can affect the suitability of the different culture systems. Greenlip abalone appear to be better suited for barrel or cage culture than Roe's abalone and seem to forage on natural food growing in the barrels as those stocked with Greenlip abalone remained free of most biofouling (Freeman et al. in Fleming and Roberts 2000, pp. 24-38).

Greenlip abalone juveniles prefer to use hides, e.g. PVC pipes when not foraging at night, or to be held in virtual darkness, but they become less reclusive as they grow (see Hindrum et al. in Burke et al., 2001, pp. 68-79).

The choice of feed type is influenced by the growout system. These may exceed A$3/kg but food conversion is quite efficient, for example 1.3 kg of dry feed for each kg of wet biomass increase including shell (Vandepeer, in Fleming and Roberts 2000, pp. 16-18).

Australian scientists and feed companies have developed world class, water stable, extruded, dry abalone feeds largely based on agricultural products (Fleming et al., in Fleming and Hone 1996, pp. 5-53).

Currently there is much greater emphasis on land-based than sea-based growout systems in Australia. A land-based system designed in South Australia for abalone culture uses 'surfboard' raceways to produce faster growth for Greenlip abalone. The raceways have a water depth of 1.5 to 2 cm (just covering the abalone) and are usually 2 m long, although they can be of any length or configuration - such as a zig-zag maze (Fleming, in Fleming and Roberts 2000, pp. 1-15). The ideal slope for a raceway is 1:100, which helps prevent mass mortalities in the event of a pump failure by allowing the bottom surface to remain wet after the tank drains. Shelters (hides) are not used in shallow raceways since they disrupt the flow characteristics in this system (see Freeman, 2001).

The water flow rate is critical because it must be sufficient to encourage feeding behaviour, maintain dissolved oxygen levels, and cause wastes to be transferred to the outlet, but not so fast as to wash away the feed. Stocking density and feed type are important factors when considering the use of this culture system. In general, higher stocking densities in land-based systems, with most of the tank floor area covered by abalone, encourage more uniform distribution of Greenlip abalone. Periodically, densities are reduced and size grading of anaesthetised abalone can be carried out (White et al., in Fleming and Hone 1996, pp. 145-151; Edwards et al., in Burke et al., 1998,pp. 116-128).

The use of this small 'surfboard' raceway system usually requires the entire operation to occur indoors. The building provides a dark environment and protects the animals from dying due to desiccation or heat stress during periods of pump failure or strong hot winds in summer or dilution of seawater during heavy rain. A much larger scale concrete tank based on the same principles of shallow depth and high current speed has been developed as a shaded, outdoor system (detailed design and management information is viewed as proprietary information).

Some growers in Tasmania and Victoria have successfully adapted the typical 'Taiwanese' culture method of using deep tanks with strong aeration and numerous shelters for refuge (Foster 1996, p 106).These tanks are designed so they can be drained regularly to remove solid wastes. They seem particularly well suited to Blacklip abalone although are also used for Greenlip abalone by some farmers. Annual survival rates (80-95% per annum) and growth rates (20-30 mm) in land-based systems with Greenlip abalone can be very high (Fleming, in Fleming and Roberts 2000, pp. 1-15) although these are not always achieved, especially as growth rates vary seasonally (Vandepeer, in Fleming and Roberts 2000, pp. 16-18).