Growth and survival of blacklip pearl oyster larvae fed different densities of microalgae MEHDI S. DOROUDI a *, PAUL C. SOUTHGATE a and ROBERT J. MAYER b a Aquaculture Department, James Cook University, Townsville, Queensland 4811, Australia; b Department of Primary Industries, Townsville, Queensland 4810, Australia (Received 17 December 1998; accepted 25 April 1999) Abstract. This paper reports on an experiment to determine growth and survival of blacklip pearl oyster, Pinctada margaritifera (L.), larvae fed a 1:1 mixture of Isochrysis aff. galbana clone T-ISO and Pavlova salina at six different densities (1, 2, 5, 10, 20 and 30  10 3 cells ml –1 ). Larval growth and survival were assessed every 4 days over a 20 day period. Exponential and logistic regression models were fitted to the growth and survival responses, respectively. Overall growth of larvae fed 5  10 3 cells ml –1 was significantly greater (p  0.01) than growth of larvae reared at other algal densities. The optimal food ration for maximum larval growth was 20  10 3 cells ml –1 , which resulted in larvae with antero-posterior shell length of 230 m after 20 days. These larvae were significantly larger (p  0.05) than those in all other treatments at the end of the experiment. Survival of larvae fed 0, 1 and 2  10 3 cells ml –1 was significantly lower than that of larvae in all other treatments at the end of 15 days (p  0.01). Maximal survival (8%) over the 20 day period was shown by larvae fed 10  10 3 cells ml –1 , while lower survival was shown by larvae fed 2  10 3 cells ml –1 (2%) and 1  10 3 cells ml –1 (0%). Key words: feeding, growth, larvae, micro-algae, pearl oyster (Pinctada margaritifera L.), survival Introduction Over recent years, hatchery production of pearl oysters has assumed greater importance for cultured pearl industries throughout the world (Gervis and Sims, 1992; Southgate and Beer, 1997). Hatchery cultured blacklip pearl oyster (Pinctada margaritifera ) spat are now produced commercially in French Polynesia, the Cook Islands, southern Japan and Hawaii. This species has been more of a problem for hatchery production than other pearl oyster species such as P. fucata and P. maxima (Coeroli et al ., 1984; Gervis and Sims, 1992) for which successful hatchery protocols are now well established (Alagarswami et al ., 1983; Rose, 1990; Rose and Baker, 1994). A major problem with hatchery culture of P. margaritifera is the low survival (generally 10%) during larval culture (Tanaka et al ., 1970; Alagarswami et al ., 1989; Southgate and Beer, 1997). This indicates that further research is needed into * To whom correspondence should be addressed at: e-mail: Mehdi.SavehDoroudi@jcu.edu.au Aquaculture International 7: 179–187, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands.