The nutritional value of seven species of tropical microalgae for black-lip pearl oyster (Pinctada margaritifera, L.) larvae

Recent years have seen major developments in the culture and availability of tropical microalgae as a food source for tropical bivalve species. The nutritional value of seven small (< 9 μm) tropical microalgae species: two diatoms (Chaetoceros muelleri and Chaetoceros sp.); three golden-brown flagellates (Isochrysis sp., Pavlova salina and Pavlova sp.) and two green-flagellates (Micromonas pusilla and an unidentified coccoid CS-126), were analysed for carbohydrate, lipid and protein contents as well as fatty acid composition. Each species of microalgae was fed singly to early (D-stage veliger) and later (umbo stage veliger) stage larvae of the black-lip pearl oyster, Pinctada margaritifera. Highest survival of D-stage larvae over the 10-day experiment was recorded for those fed Pavlova sp. (CS-50). Greatest shell growth was shown by D-stage larvae fed the golden-flagellates Pavlova sp. (CS-50) and Pav. salina. Based on growth of D-stage larvae, the microalgae could be divided into three groups: (1) larvae fed Pav. salina and Pavlova sp. showed significantly greater growth than those fed other microalgae; (2) those fed Isochrysis sp., C. muelleri and M. pusilla showed significantly greater growth than unfed larvae; and (3) larvae fed Chaetoceros sp. and CS-126 did not grow at a rate greater than unfed larvae. Growth of D-stage veliger larvae was significantly correlated with carbohydrate, lipid and protein content of microalgae and with levels of dietary polyunsaturated fatty acid, specifically DHA (r = 0.829, P = 0.021). In a second experiment survival of umbo-stage larvae (including the unfed control) did not differ significantly between treatments (P < 0.05) after 8 days of culture. Larvae fed Pavlova sp. and Pav. salina showed the greatest incremental growth increases, but these were not significantly greater than those of larvae fed TISO and C. muelleri (P > 0.05). Growth of umbo-stage larvae fed M. pusilla, Chaetoceros sp. and the Prasinophyta sp. (CS-126) did not differ significantly from that of unfed larvae (P < 0.05). This study is the first comprehensive assessment of the nutritional value of tropical microalgae species for pearl oyster larvae. The results provide a basis for development of more effective larval culture techniques by identifying microalgae supporting good growth of P. margaritifera larvae of different ages.