## 4 Conclusions  
The strains of _Picochlorum costavermella_, _Picochlorum oklahomense_, _Microchloropsis gaditana_, and _Nephroselmis pyriformis_ were easily cultivated in an open raceway pond under controlled conditions, producing significant amounts of cellular metabolites. Intriguingly, strains such as _P. costavermella_ VAS2.5 and _N. pyriformis_ PAT2.7, for which the available literature is limited, seem to be potential new candidates and subjects for biotechnology study. Specifically, _Picochlorum_ strains and _M. gaditana_ VON5.3 produced notable amounts of lipids, which were dominated by polar lipids that were rich in PUFAs, especially [45; 8; 11; 14; 17]C20:5 and [49; 12; 15]C18:3. Therefore, even though the stage of the current research does not yet establish the suitability of the aforementioned strains for utilization in large-scale applications, these strains pose as enticing candidates for further trials. On the other hand, _N. pyriformis_ PAT2.7 proved to be weaker in lipid production compared with to the other tested strains, and its lipids were dominated by neutral ones, which, though, contained large quantities of [49]C16:1, a fatty acid of great biotechnological interest. Moreover, all tested strains accumulated great amounts of polysaccharides and proteins, and overall, they demonstrated a well-balanced amino acid profile with high levels of lysine and threonine. Therefore, these strains have proved to be excellent alternative protein sources for fish feed. Lastly, the two _Picochlorum_ strains and _M. gaditana_ VON5.3 synthesized pigments in amounts comparable to other studies, while _N. pyriformis_ PAT2.7 pigment  
\begin{table}
\begin{tabular}{l c c c} \hline  & **Sum of EAA** & **Sum of NEAA** & **EEAA/NEAA** \\ \hline _P. costavermella_ VAS2.5 & 20.6 \(\pm\) 0.6 & 21.2 \(\pm\) 0.2 & 1.0 \(\pm\) 0.0 \\ _P. oklahomense_ SAG4.4 & 21.8 \(\pm\) 0.5 & 24.1 \(\pm\) 0.5 & 0.9 \(\pm\) 0.0 \\ _M. gaditana_ VON5.3 & 19.6 \(\pm\) 0.3 & 20.6 \(\pm\) 0.0 & 1.0 \(\pm\) 0.0 \\ _N. pyriformis_ PAT2.7 & 28.7 \(\pm\) 1.1 & 30.4 \(\pm\) 0.5 & 0.9 \(\pm\) 0.0 \\ \hline \end{tabular}
\end{table}
Table 6: Essential and non-essential amino acid ratio of the microalgal strains that were cultured in an open raceway pond photobioreactor. The presented values are the average of two batches.  
production was lower. Overall, the results of the present study provided strong evidence for the validity of the hypothesis of exploitation and potential in the use of indigenous microalgal strains for the development of high-interest applications.  
Conceptualization, A.T., D.V.V. and G.A.; methodology, P.D., S.P. and Y.K.; formal analysis, P.D., S.P. and D.K.; investigation, P.D., S.P., D.K. and Y.K.; data curation, P.D., S.P., D.K. and E.R.; writing--original draft preparation, P.D., S.P. and Y.K.; writing--review and editing, E.R., Y.K., A.T., D.V.V. and G.A.; project administration, G.A.; funding acquisition, G.A. and P.D. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the project \"Isolation of microalgae native to the Ionian Sea and their use in the production of high added value products--IonianAlgae\" (MIS 5045862, FK 80967). The project \"IonianAlgae\" was co-funded by the Greek State (Greek General Secretariat for Research and Technology) and the European Union. The research work was also supported by the Hellenic Foundation for Research and Innovation (HFRI) under the 3 rd Call for HFRI PhD Fellowships (Fellowship Number: 6587).  
Not applicable.  
The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.