This paper reports on two factorial design experiments conducted to examine the combined effects of algal ration and larval density on growth and survival of black lip pearl oyster Pinctada margaritifera (L.) larvae. In the first experiment, 1-day-old larvae were cultured for 7 days at densities of 1, 2 and 5 mL(-1) and fed algal rations of 0, 2.5, 5 or 12.5 x 10(3) cells mL(-1). In the second experiment, 13-day-old larvae were cultured for 7 days at the above densities and fed algal rations of 0, 7.5, 15 and 37.5 x 10(3) cells mL(-1). Algal rations in both experiments were composed of a 1:1 mixture of the flagellates Isochrysis aff, galbana clone T.ISO and Paplova salina. Response surface contour diagrams were generated from growth and survival data to estimate optimal culture conditions. Results showed that, within a suitable larval density range, growth of P. margaritifera larvae was significantly (P < 0.01) influenced by algal ration. At the end of the first experiment, greatest survival occurred at a ration of 4.5-11.5 x 10(3) cells mL(-1) and at a larval density of less than or equal to 3 mL(-1). Greatest antero-posterior shell length was shown by larvae fed between 4.5 x 10(3) and 11.5 x 10(3) algal cells mL(-1). In the second experiment, greatest: antero-posterior shell length occurred within an algal ration range of 15-32 x 10(3) cells mL(-1). The greatest survival occurred below an algal ration of <2.5 x 10(3) cells mL(-1); however, this algal ration supported poor algal growth. The results indicate that, to maximize growth and survival, P. margaritifera larvae should be fed at an algal ration of approximate to 8 x 10(3) cells mL(-1) and cultured at a density of three larvae mL(-1) up to 8 days of age. Older (13- to 20-day-old) larvae should be cultured at a density of < 2 mL(-1) and fed an algal ration of approximate to 25 x 10(3) cells mL(-1).
