Effects of different harvesting and processing methods on Nannochloropsis oculata concentrates and their application on rotifer Brachionus sp. cultures

The effects of the cell separation method and the biomass processing of Nannochloropsis oculata were evaluated with respect to the cultivation performance of rotifers (Brachionus sp.). The algal culture was harvested by centrifugation or flocculation, and the biomass separation efficiency and the concentration factor were determined. The biomass was processed by chilling, freezing, heat-drying, or freeze-drying; and the cell integrity, resuspension percentage, and sedimentation profile of the diets were evaluated. The zootechnical performance (maximum rotifer density, growth rate, maximum egg production, fecundity, and feed ingestion rate) of rotifer cultures that fed the concentrated diets was compared with feeding the fresh culture of N. oculata (control treatment). Centrifugation resulted in 97% separation efficiency and a concentration factor of 578 and flocculation followed by centrifugation showed an efficiency of similar to 100% and concentration factor of 444. The harvesting technique did not have a significant influence on the characteristics of the diets and also on the zootechnical performance of the rotifers. The characteristics of the chilled concentrates (cell integrity, resuspension percentage, and sedimentation profiles) were similar to the control treatment, and the rotifers fed on those diets had the highest growth performances. Rotifers fed on frozen diets presented the worst performances. The heat-dried diets presented the lowest cell viability percentages, lowest resuspension percentages, and higher sedimentation rates. The feed ingestion rates of these diets were the lowest, resulting on inferior growth performance of the rotifers. In summary, both harvesting methods could be used, and chilling is the most recommended method for processing N. oculata biomass.