Sterols are vital components of all eukaryotic cells. This review describes the variety of sterol structures found in microalgae, yeasts, fungi, protozoans and microheterotrophs. Reports of the occurrence of sterols in prokaryotic cells are critically assessed. Methylotrophic bacteria contain unusual 4-methylsterols, but reports of 4-desmethyl sterols in cyanobacteria and other bacteria are limited and many of these seem dubious. Possible application areas for sterols derived from mass culture of microalgae and other microorganisms are highlighted.

Deep-sea sharks (mainly dogfish) are a significant by-catch of trawls for the deep-water fish orange roughy (Hoplostethus atlanticus). To test whether the livers of these sharks might be a source of commerically valuable squalene and other lipids, 16 sharks of 8 species were collected from Tasmanian waters at depths of 700-1200 m during research cruise S02/88 of FRV Soela. The sharks were Centroscyrnnus crepidater (longnose velvet dogfish), Centroscyrnnus owstoni (Owston's dogfish), Centroscyrnnus coelolepis (Portuguese dogfish), Deania calcea (shovelnose dogfish), Etmopterus baxteri (Baxter's dogfish), Etmopterus sp. nov. (unnamed dwarf dogfish), Dalatias licha (kitefin or seal shark) and Centrophorus squarnosus (leafscale gulper shark). Squalene content, triacylglycerols, diacylglyceryl ethers, total fatty acids, pristane and other lipids were analysed by capillary gas chromatography and thin-layer chromatography-flame ionization detection. The livers contained high levels of squalene (15-69% by weight), except for the liver of C. squarnosus (I%), which had an unusually high amount of diacylglyceryl ethers (79%). Triacylglycerol and diacylglyceryl ether contents in the livers ranged from 1 to 26% and from 7 to 79% by weight respectively. The C19 isoprenoid alkane pristane was a minor constituent in all samples (0.01-0.56% by weight of liver). The three major esterified fatty acids in all samples were palmitic (16:0), oleic [18: 1 (n - 9)] and eicosa-11-enoic [20: 1 (n - 9)] fatty acids. Polyunsaturated fatty acids were minor constituents. These data indicate that shark livers could provide a profitable by-catch from deep-water trawls, but it is unlikely that shark could form the basis for a target fishery due to their susceptibility to overfishing.

The lipid and fatty acid compositions of rotifers (Brachionus plicatilis) fed on yeast or on the unicellular prymnesiophyte Pavlova lutheri, an alga commonly used in Australian hatcheries, were compared by TLC-FID, GC and GC-MS. Significantly higher relative proportions of energy-rich triacylglycerol were present in the Pavlova-fed rotifers than in the yeast-fed animals, and total lipid content reached a maximum between 12 and 24 h. High incorporation of the essential fatty acids eicosapentaenoic acid (EPA; 20: 5ω3) and docosahexaenoic acid (DHA; 22:6ω3) occurred in the Pavlova-fed rotifers. EPA and DHA content was 11.6% of total fatty acids after 3 h of feeding and reached 20 and 23% after 24 and 48 h respectively. The proportion of essential fatty acids in rotifers fed Pavlova compares very favourably with data obtained by overseas workers using a variety of microalgae and dietary supplements. On the basis of fatty acid composition alone, these results confirm the suitability of P. lutheri as a feedstock for Australian mariculture operations.