Utilization of a liquid fertilizer to improve Rhodomonas sp. lipid composition for aquaculture purposes

Abstract

The microalga Rhodomonas sp. is important as live feed for copepod production. Thus, improving its growth and biochemical composition is essential for aquaculture. In this work, the utilization of a liquid fertilizer as an alternative growing medium of Rhodomonas sp. was studied. The strain was grown in cultivation bags at a final volume of 5 L at 15°C ± 1°C, light intensity of 60 μmol photons m-2 s-1 and under continuous light. Both culture conditions were prepared using sterile seawater and then adding B1 (1mL/L) culture medium (control) or liquid fertilizer (1mL/L) (fertilizer condition). Then, cell density, dry weight, lipid content and fatty acid composition of Rhodomonas sp. were determined. The use of fertilizer induced an increase in cell number and dry weight. In addition, triacylgliceride and sterol content significantly increased when Rhodomonas sp. were grown in the presence of fertilizer. Fatty acid composition showed that the percentage of eicosapentenoic (EPA, C 20:5n3) and docosahexaenoic (DHA, C 22:6n3) fatty acids (FAs), the most required by copepods, significantly increased at expense of palmitic (C 16:0) and oleic (C 18:1n9) FAs. Finally, both Rhodomonas sp. cultures (control and fertilizer conditions) were used as living food for the native copepod Acartia tonsa, isolated from Bahia Blanca?s Estuary. Then, the reproductive success was measured in terms of egg production. The results revealed that Rhodomonas sp. grown in the presence of fertilizer induced a significant increase in the total number of eggs. Thus, the results presented suggest that microalgal biochemical composition directly impacts on copepod reproduction, supporting the importance of this study to improve the production of native aquatic species for aquaculture purposes.