Microalgae are used in mariculture as live feeds for all growth stages
of molluscs, for the larval stages of crustaceans and some fish speci
es, and for zooplankton used in mariculture food chains. In order to b
e nutritionally sufficient, microalgae must supply a balanced mixture
of nutrients. We have studied the biochemical composition of about 40
species of microalgae from seven algal classes to define those that ma
y be best adapted to the Australian conditions. Microalgae varied in t
heir proportions of protein (6-52%), carbohydrate (5-23%) and lipid (7
-23%). All species had similar amino acid composition, and were rich i
n the essential amino acids. Microalgal polysaccharides were variable
in sugar composition, but most had high proportions of glucose (21-87%
). Diatoms, prymnesiophytes, cryptomonads and eustigmatophytes were ri
ch in one or both of the 20:5(n - 3) and 22:6(n - 3) polyunsaturated f
atty acids important for marine fish larvae (5-35% total fatty acids),
prasinophytes had low to moderate levels of one of the acids (4-10%)
whereas chlorophytes were deficient in both acids (0-3%). All species
had relatively high concentrations of ascorbic acid (1-16 mg g(-1) dry
weight) and riboflavin (20-40 mu g g(-1)). The likely nutritional val
ues of the microalgae, based on their biochemical composition, are dis
cussed. (C) 1997 Elsevier Science B.V.