Microalgae cultivation as a food source in aquaculture applications

Laura Alejandra Lamilla Tamayo

Master's thesis

Abstract:

Microalgae play a very important ecological role in both aquatic and terrestrial ecosystems and represent one of the most efficient converters of solar energy to biomass. Because of those characteristics, microalgae have been used in plenty of industrial and biotechnological processes and have attracted interest for their potential to generate valuable products in high volumes. Some of those applications include the use of microalgae cultured in intensive systems for aquaculture and animal nutrition. The majority of microalgae world requirements for aquaculture goes to mollusks, as economically and ecologically important filter feeders there has been an increased interest in research for algae production focused in this group, however much of the research is sparse and varied with no single general trend, moreover the majority of studies are focused on marine bivalves, with freshwater bivalves having much less attention. In this thesis we aim to review the current knowledge on the use of unicellular and simple multicellular microalgae in aquaculture especially for rearing bivalves, as well as finding general trends and patterns of research in the topic. Additionally, we developed a protocol for the establishment of a pilot culture of algae aimed to feed freshwater mussels and assessed the algal culture early growth using image analysis techniques under different growth conditions. The bibliometric analysis retrieved a total of 287 peer reviewed articles clustered in 6 groups the most important ones consisting of (i.) terms related to potential harmful consequences of the microalgae, (ii.) nutritional value of microalgae diet, (iii.) nutritional elements necessary to rear bivalves. A total of six bivalve species are the most co-occurent of the 287 peer-reviewed articles, all of them inhabit marine ecosystems and are reared because of their meat (except for Pinctada margaritifera, Margaritidae), regarding the algae species the search found a total of 13 most relevan species, all of them naturally distributed salty or brackish water.Concerning the pilot culture, our protocol using Ettlia oleobundans, produced a viable mid-size culture of size 2.28 x107 cells/mL and a 90% of viability after two months of culturing. On the other hand, early growth assessed through image analysis showed that for the group of pictures taken after 20 days a stronger contrast was identifiable, the Anova found a significant effect of the media used during acclimatization (Pr(>F) <0.01), algae that were acclimatized in agar before the start of small-scale experiment were significantly greener, and hence, denser, than algae acclimatized in liquid media. The mean Hue value for algae acclimatized in agar was 68.49 ± 5.80, while the liquid acclimatized algae 62.39 ± 4.46. Additionally, the mean Hue value for the three different evaluated concentrations was as follows: A=65.99 ± 5.37, B=66.79 ± 8.23, and C=63.41 ± 3.21. The concentration of F/2 media showed no significant effect (Pr(>F) 0.22). The method seemed promising for evaluating growth in algae, especially in early stage although the presence of some outliers in the data produced by the limitations of the image taking and processing algorithm deserve further research.

Keywords

bibliometric networks, bivalve rearing, Ettlia oleoabundans, culture setup, Image analysis, Hue value

Language used: English

Date on which the thesis was submitted / produced: 24. 7. 2020

Thesis defence

• Supervisor: RNDr. Milan Skalický, Ph.D.

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Master programme / field:
Natural Resources and Environment / Natural Resources and Environment