Summary

This report refers only to work undertaken by staff at NSW Fisheries dealing with technological development of harvesting, preservation, storage and feeding of micro-algae. The results of complementary research to evaluate tubular photo-bio-reactor culture of micro-algae for marine hatcheries is the topic of a separate report by Michael Borowitzka, Murdoch University, W.A.

Micro-algae are essential for commercial rearing of many aquatic animals, especially the larvae and juveniles of bivalve molluscs, penaeid prawns and live food organisms such as rotifers used to hatchery rear marine fin-fish and crustaceans. Recent surveys conducted in Australia and overseas have revealed that 30 - 40% (max.70%) of marine hatchery operating costs can be attributed to micro-algal culture. The problem of high costs of individual hatcheries producing their own algae is compounded by the need of scarce expertise, without which crashes of algae at critical periods occur quite commonly.

The aims have been to develop reliable cost efficient methods for centralised large-scale production, concentration, storage, preservation, transportation and resuspension of micro-algae over a suite of species that collectively meet the needs of all types of marine hatcheries throughout Australasia. These include penaeid shrimp, finfish and bivalve hatcheries that account for the great bulk of micro-algal production and use.

This report describes trials and tribulations encountered in the development of successful harvesting, preservation and storage techniques. These techniques have had to be customised for each of seven individual species of micro-algae in order to achieve a minimum practical shelf life of 4 to 6 weeks. Pleasing results have been achieved with stored concentrate diets which have yielded growth rates of 80% or greater than those supported by live algae control diets.