Laboratory scale photobioreactor for high production of microalgae Rhodomonas salina used as food for intensive copepod cultures

Research output: Contribution to conferencePosterResearchpeer-review

Abstract

Introduction
Microalgae are essential feeds for many cultured molluscs, larvae of marine fishes, crustaceans as well as other important live feeds including rotifers, Artemia and copepods (Muller-Feuga, 2000). Microalgae are grown either in open culture systems (ponds) or closed systems (photobioreactor - PBR). There is an increasing interest in using closed PBRs for algae cultivation since this culture system provides a better control of cultivation conditions and enables higher algae productivity. Among the marine microalgae, the cryptophyte Rhodomonas salina is one of the optimal feed for copepods (Støttrup and Jensen, 1990; Zhang et al., 2013). Despite the benefit of using R. salina in cultivation of copepods, to our knowledge, there is no report on the production of this microalga at industrial scale to supply sufficient food for mass production of copepods. We intend to conduct the basic tests on a laboratory scale PBR and upscale in the next phase. In the present study, R. salina was cultivated in laboratory scale tubular PBRs (2 × 45 l) for 18 to 30 days where the growth, biochemical composition and production of R. salina were recorded.
Materials and methods
The Rhodomonas salina was cultivated continuously at temperature of 20ºC and salinity of 30ppt in two tubular PBRs with addition of CO2. The experiment was run two times and each PBR in 18 - 30 days. Periodically, the algae were sampled for analyzing the growth, biochemical composition and production. An exponential light model was used to estimate the optimal cell density of R. salina in the PBRs. This model estimation was validated by the collected data from PBR experiments. As a result, suggestions for further improving of the PBR performance were provided.
Results and discussions
The maximal specific growth rate of R. salina in PBRs was 0.84 ± 0.17d-1 which was in the high range reported elsewhere for this species (Bartual et al., 2002 and references therein). We enabled to maintain a cell density of ca. 2.2 × 106cells.ml-1 continuously for 2 - 3 weeks with a daily dilution rate of 0.42 ± 0.03d-1. Interestingly, at this cell density, we were able to maintain the good quality of algae with high content of total fatty acids (32 - 46pg.cell-1) and more than 2/3 of the fatty acids are polyunsaturated fatty acids which are the desired components for copepods. We also succeed in running the PBRs for a longer period (2 -3 months) at the density from 2 - 2.5 × 106cells.ml-1 with a daily dilution rate ca. 0.4d-1; however, the biochemical composition of the algae was not exanimated. The present algal production enables to feed for ca. 400 l of copepod culture at density ca. 2500ind.l-1. Assuming that the female ratio of copepod culture was 0.45 and 1/3 of the food ingestion in female was assimilated into egg production; this algal PBR system can sustain a copepod culture which can provide a daily total egg production of 10 - 14 × 106 copepod eggs. The achievement of high cell density in the PBRs was close to the optimal cell density of 2.5 × 106cells.ml-1 estimated by the light model. From the light model, we can see that the diameter of the current PBRs (Ø = 20cm) is the limiting factor to increase the algae production. The PBRs has a potential for further improvement to achieve higher algal production when we aim at the next phase, the industrial scale.
Conclusion
The microalgae Rhodomonas salina was successfully cultivated in laboratory scale PBRs, which allow achieving high algae quality at the optimal growth, ready to feed out to copepod cultures.
Original languageEnglish
Publication date20 Oct 2015
Publication statusPublished - 20 Oct 2015
EventEAS40: European Aquaculture Society - Rotterdam, Netherlands
Duration: 21 Oct 201523 Oct 2015

Conference

ConferenceEAS40
CountryNetherlands
CityRotterdam
Period21/10/201523/10/2015

Cite this