Nutritional properties of microalgae for mariculture

Microalgae are used in mariculture as live feeds for all growth stages of molluscs, for the larval stages of crustaceans and some fish species, and for Zooplankton used in mariculture food chains. In order to be 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 may be best adapted to the Australian conditions. Microalgae varied in their proportions of protein (6–52%), carbohydrate (5–23%) and lipid (7–23%). All species had similar amino acid composition, and were rich in 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 rich in one or both of the 20:5( n-3) and 22:6( n-3) polyunsaturated fatty 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 μg g −1). The likely nutritional values of the microalgae, based on their biochemical composition, are discussed.