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Abalone Nursery Phase


 

Towards the end of larval development, the larvae sink to the bottom of the container and begins exploring on its foot for a suitable surface for settlement.The larvae are transferred to the tanks used for settlement when the larvae display this typical gliding or creeping behaviour. The settlement tanks contain vertical PVC sheeting covered with a film of diatoms or other algae.

Settlement and metamorphosis occur typically within one to three days after the larvae are introduced into the tank. The transition from a free-swimming larva to a juvenile, living permanently on a hard surface, is a critical phase in the life of an abalone and mortality can be very high (~90%) although the technology is improving (Daume, 2002). This mortality rate is compensated by the high fecundity of the adults (1 to 5 million eggs and 100s of million sperm).

 

 
 

Feeding and Growth

The newly settled juvenile abalone begin feeding on bacteria and diatoms that naturally occur on the surfaces of the settlement plates and tank walls (Daume,2001).Diatom growth is stimulated on the plates within long, aerated tanks, by adding nutrients to the water, as needed, and ensuring long exposure to sunlight either outdoors or in greenhouses. Survival may only be 5-20 per cent through settlement and nursery phases. (Fleming, in Fleming and Roberts 2000, pp.1- 15). However, controlling the type of algae on the plates can greatly improve settlement and juvenile growth rates (Daume, 2001) although Algae cultures can be added and shading and turbulence manipulated to influence algae composition.

In general, the nursery phase has been identified by industry as a high priority area for further research because of its commercial significance.

Various intermediate systems, such as shallow round tanks or enclosed PVC pipes, have been used in Australia to grow abalone, after removal from plates, before stocking into growout systems.

Informtation courtesy of the WA Department of Fisheries

 

 

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