Farming Abalone

Hatchery Phase

High quality gametes for hatchery production are most easily obtained during the natural spawning period in the wild, although this has proved to be difficult with Roe's abalone populations near Perth.The peak spawning period is around March to August for Roe's, and October to December for Greenlip abalone in Western Australia (Freeman, 2001). Techniques to condition broodstock in order to encourage development of mature eggs, have been studied (Fleming 2001).High quality gametes can now be obtained in winter from wild Greenlip abalone held in a flow through broodstock system developed by researchers from this Department and industry (Freeman et al., in Fleming and Roberts 2000, pp. 55-60). Maintaining very stable, warm (for example 17.5^o) water temperatures seems critical to avoiding uncontrolled spawnings in this system. Other Australian groups are also having success with broodstock systems, for example with wild Blacklip abalone, including one involving a recirculating system (Savva et al., in Fleming and Roberts 2000, pp. 61-76). Some Australian farmers now use farmed stock as broodstock quite successfully as abalone tend to mature at a smaller size when farmed.

The induction of spawning is well understood in abalone and can be stimulated with single, or combinations of, stimuli including temperature changes, seawater treated with UV, ozone or hydrogen peroxide, handling, or exposure to air, depending on the species of interest. Males and females are spawned in separate containers (usually 15 - 60 litre buckets or tanks) to be sure the gametes are isolated before fertilization. Spawning usually occurs six to eight hours (males) and ten to twelve hours (females) after initiation of the spawning induction.

After spawning, the eggs are siphoned from each bucket and passed through a plankton mesh screen of 300 microns (1 mm = 1000 microns µm) to remove any debris. The eggs are counted, fertilised and the excess sperm is washed off. Fertilised eggs are placed in a container with a wide flat bottom to form a monolayer of eggs.

Fertilized eggs hatch after approximately 16 hours at 18^o and are called trochophore larvae. Newly hatched trochophore larvae swim to the surface and then can be easily separated from the unhatched eggs and discarded egg cases by decanting off the top water layer into a clean tank for subsequent larval rearing. In flow-through tanks, surface larvae overflow into the larvae rearing tanks.

These non-feeding larvae develop over about five days at 17^o to 18^o and about four days at 20^o. Therefore, the management during the larval period consists of maintaining densities at 25 per ml or less, ensuring the highest water quality, and reducing the chances of bacteria growing on the tank surfaces. Survival rates of over 80 per cent are not uncommon if proper care is taken during larval rearing (Fleming, in Fleming and Roberts 2000, pp. 1-15).

There are two different methods that can be used during larval rearing: static culture and flow-through, as is the case in commercial oyster hatcheries. In the static method, the larvae are reared in very large tanks or containers (5-20 cubic metres) without a continuous inflow of seawater.The water in each container is changed periodically, for example, every one to two days. Small-scale batch (static) systems can be used for research trials. Most hatcheries in Australia use a flow-through system in small tanks (about 200 litres). The larvae remain in the same tank or are possibly changed once during the larval rearing period.

A comprehensive hatchery manual is available (Hone et al., 1997).