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The marine centric diatom Chaetoceros muelleri has been widely used as live feed in fish and shellfish aquaculture due to its excellent nutritional properties. The growth of microalgae is affected by various nutritional and environmental parameters, and species specific optimization of these parameters is essential for the development of cost-effective biomass production process. In this study, the growth of C. muelleri, was optimized using response surface methodology ( RSM). The variables nitrate, phosphate, silicate, temperature, pH, salinity and agitation speed were initially screened for biomass production in C. muelleri using Plackett-Burman experimental design, and it was found that nitrate, phosphate, silicate, temperature and pH significantly influenced the biomass production. These variables were further optimized by central composite design of RSM for biomass production and nutrient composition, and the medium was re-constituted accordingly to have 180 mg L−1 nitrate, 7.5 mg L−1 phosphate, 30 mg L−1 silicate, with optimum growth conditions of temperature at 31°C and pH 6.46. At the end of 10 days culture period under the above conditions, biomass, protein, lipid and carbohydrate significantly increased from 0.360 ± 0.01 mg L−1, 9.41 ± 0.02%, 18.11 ± 0.01%, 0.6 ± 0.02% to 1.16 ± 0.01 mg L−1, 11.02 ± 0.01%, 19.58 ± 0.01% and 0.77 ± 0.01% respectively. The biomass production of C. muelleri could be increased 3.2-fold with an improved nutrient profile by modifying the growth factors, the study thus offering an optimized process for biomass production of C. muelleri. [ABSTRACT FROM AUTHOR]

Oyster seed production in hatchery and nursery systems has relied on the production of microalgae, which is cost effective, but often unpredictable. The development of a satisfactory substitute diet would greatly reduce production costs of hatchery operations. Single cell detritus ( SCD) production from seaweed ( Porphyra haitanensis) may have great potential as a partial substitute for microalgae. In this experiment, a technique for producing SCD was developed and the product was used as a partial substitute for microalgae for the nursery culture of juvenile tropical oysters ( Crassostrea belcheri) in a hatchery setting. A reverse osmosis technique was used on ground seaweed (particle size <200 μm) immersed in freshwater and placed on a shaker at 100 rpm for 2 h before being returned to seawater. This technique was shown to be highly effective for SCD production with a density of 33.7 ± 7.0 × 104 cell mL−1 and the percentage of SCD particle diameter <20 μm was 89.2%. A partial replacement of microalgae with SCD was found to be unsuitable for nursing oyster larvae. For juvenile oysters (shell width 1.85 ± 0.03 mm and shell length 1.78 ± 0.06 mm) substituting 75% of microalgae with SCD showed lower absolute shell growth, and lower daily yields and survival rates when compared to rates substituting 50% or lower substitution with SCD, or 100% microalgae ( P < 0.05). It was found that substituting 50% of the traditional microalgae with SCD produced from seaweed ( P. haitanensis) can be used as a partial microalgae substitute for the nursery culture of the juvenile tropical oyster. [ABSTRACT FROM AUTHOR]

A local algal isolate Tetraselmis tetrathele was studied to determine the suitable levels of three growth factors (nutrient medium, light intensity and photoperiod) for mass culture. Significantly higher population cell count (141.92 × 104) were found in 4-day-old cultures (exponential phase) enriched with Conwy medium and exposed continuously to 93.31–103.5 μmole photon m−2 s−1 light intensity compared with two other media (F, SEAFDEC/AQD) under the same light conditions. Cultures exposed to higher levels of photosynthetic photon flux density and continuous photoperiod had a significantly higher cell count regardless of nutrient media used. The chemical composition of T. tetrathele varied as the culture aged. Significantly higher crude protein (49.6%) and crude ash (15.9%) were found in cultures harvested at exponential than at stationary phase of growth. In contrast, significantly higher carbohydrate (55.2%) was noted as the culture aged. There was an increase in the percentage of saturated, monoenoic and n-3 highly unsaturated fatty acids at the stationary phase of growth. Addition of filtrate from various phases of growth and from 10-day-old cultures at various concentrations stimulated cell growth of T. tetrathele. This study identified the optimum growth conditions for mass culture of T. tetrathele and demonstrated its change in the chemical composition as the culture aged. [ABSTRACT FROM AUTHOR]