Ingestion and Utilization of Microalgae with Different Characteristics by Pearl Oyster Pinctada fucata Larvae.

Nannochloropsis oculata, Isochrysis galbana and Chaetoceros muelleri are tropical microalgae that have different shapes, particle sizes, surface structure, and biochemical compositions. As these species are easy to cultivate, can endure high temperatures, and are rich in unsaturated fatty acids, they are widely used in tropical and subtropical regions for invertebrate larval rearing. These three microalgae species were tested for ingestion, digestion, growth and survival of Pinctada fucata larvae, using an optical microscope, in order to identify an appropriate diet for P. fucata. An experiment was conducted using larvae at 2 dph (days post hatching) (shell length: 79.01 ± 2.00 µm), 8 dph (90.81± 4.61 µm), 14 dph (108.81 ± 6.58 µm), and 20 dph (146.83 ± 8.92 µm). Larvae were stocked in flasks and fed 105 cells/mL of each species of microalgae individually. Larvae were fed for one hour and then observed under the microscope to detect ingestion. Larvae were then sieved and placed in flasks containing filtered seawater to measure the area of microalgae in the stomach, and to analyze the digestion of the microalgae ingested every two hours. Of the three species, N. oculata and I. galbana were ingested at any stage, while C. muelleri were not ingested at all, and the ingestion rate of N. oculata was higher than that of I. galbana. In addition, I. galbana were easily digested, and N. oculata were difficult to digest. Subsequently, growth and survival rates were determined by feeding larvae N. oculata and I. galbana. Better growth and survival rates were observed in the larvae fed with I. galbana. The un-ingestible algae could not be used by the larvae, and high concentrations of algae were detrimental to larval growth and survival. These findings suggest that the microalgae used as staple foods in the larval culture practice of P. fucata should consist of small particle size, spherical shape, smooth surface, and should be easily digested. In addition, algae should be fed to larvae at appropriate concentrations and times. [ABSTRACT FROM AUTHOR]