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CULTIVATION OF TETRASELMIS STRIATA UNDER OPTIMIZED GROWTH CONDITIONS AND BIOMASS QUALITY EVALUATION FOR FISH FEED PRODUCTION

Patrinou V.¹*, Daskalaki A.², Kampantais D.³, Economou C.N.⁴, Bokas D.⁵, Kanakis D.C.³, Aggelis G.², Vayenas D.V.⁴, Kotzamanis I.³, Tekerlekopoulou A.G.¹

¹ Department of Environmental Engineering, University of Patras, 2 G. Seferi Str., 30100, Agrinio, Greece

² Department of Biology, University of Patras, 26500, Patras, Greece

³ Hellenic Centre for Marine Research / Institute of Marine Biology, Biotechnology and Aquaculture, Iera Odos 75, 11855, Athens, Greece

⁴ Department of Chemical Engineering, University of Patras, 26500, Patras, Greece

⁵ PLAGTON S.A., Thesi Konaki Skentou, Dimos Xiromerou Aitoloakarnanias, Greece

INTRODUCTION

EXPERIMENTAL PROCEDURE AND RESULTS

CONCLUSIONS

In this study, a marine strain of Tetraselmis striata was cultivated in drilling waters obtained from the facilities of the commercial fish farm Plagton S.A.. Important growth parameters for microalgae were optimized by modulating substrate composition, pH and temperature. The waters (salinity of 29‰) were enriched with the commercial fertilizer Nutri-Leef 30-10-10. Optimum fertilizer growth quantity was found to be 0.2 g L^-1, while optimum growth conditions were recorded as pH 8 and temperature 25^oC that lead to a maximum biomass productivity of 79.8 mg L^-1 d^-1 and a specific growth rate of 0.16 d^-1. The biomass of Tetraselmis produced in these optimized conditions was rich in metabolites and especially crude protein (51.3%) but essential amino acid content was also recorded. Analysis of the fatty acids revealed high percentages (up to 14%) of eicosapentaenoic acid (EPA).

Aiming to minimize production costs that could enable full-scale cultivation, the commercial fertilizer Nutri-Leef (30% -TN, 10% -P, 10% -K) with an inorganic carbon source (NaHCO₃) was tested as a growth medium for Tetraselmis. Initially, different quantities of Nutri-Leef - 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 g per litre - were tested at 25 ±1^oC under uncontrolled pH, while 0.18 g L^-1 of NaHCO₃ was added to all experimental sets. High biomass productivities were recorded for the added fertilizer quantities of 0.1 and 0.2 g L^-1 (productivities: 106.8 and 134.6 mg L^-1d^-1) (Table 1). However, for fertilizer quantities over 0.4 g L^-1, biomass yields gradually reduced, with productivities ranging from 60.8 to 92.3 mg L^-1d^-1. A similar trend was also seen for the lipid yields, indicating that as the fertilizer increased in quantity, the lipid content decreased. The optimum fertilizer quantity was found to be 0.2 g L^-1 which led to the highest biomass productivity and enhanced lipid content (16.3%).

Using the optimum fertilizer quantity, the pH values of 7 and 8 were then tested at 25 ±1^oC. Of these pH values, pH 8 presented the highest biomass productivity of 79.8 mg L^-1 d^-1 and maximum oil content of 26.4%, while pH 7 affected only biomass productivity (60.1 mg L^-1 d^-1) but not lipid content (Table 2). The effect of temperatures 19 ±1 and 25 ±1^oC was then examined under the optimum pH (8). The highest biomass yield was recorded at 25 ±1^oC (Figure 1) and the lipid content increased slightly at 19 ±1^oC. Evaluation of biomass quality revealed T. striata produced under the identified optimum growth conditions was rich in lipids, carbohydrates, proteins and pigments (26.4%, 18.3%, 51.3% and 3.6%, respectively) (Table 3). Amino acid analysis showed that the optimized biomass had high essential amino acid content (22.7%) and a high essential to non-essential amino acid ratio (EAA/NEAA) of 0.96 (Table 4). Fatty acid analysis revealed that the biomass contained high EPA content in all growth conditions (10-14%).

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Under the optimized growth conditions the microalga Tetraselmis striata was able to produce high quality biomass rich in significant amounts of crude protein and polyunsaturated fatty acids such as EPA, indicating its suitability for incorporation into conventional fish feed products.

Table 4. Amino acid profiles of T. striata cultivated in different

growth conditions.

Table 1. Results obtained while employing different fertilizer quantities.

Table 3. Evaluation of T. striata biomass quality under different growth conditions.

Table 2. Effects of pH and temperature on biomass productivity and lipid

content of T. striata.

Figure 1. T. striata biomass production under different growth conditions.

Acknowledgement: This project (AlgaFeed4Fish, MIS 5045858, FK 80916) was co-founded by the European Regional Development and National Resources Secretariat for Research.