Fatty acid composition in trochophores of mussel <i>Mytilus galloprovincialis</i> grown under contamination with polychlorinated biphenyls
Status of <i>Mytilus galloprovincialis</i> populations in the natural habitat is known to directly depend on development of Black Sea mussel at all its stages, including initial stages of larval ontogenesis, which are very sensitive to environmental pollution. Organic pollutants adversely affect mussel larvae by inhibiting their growth and development. Patterns of mussel reproduction are well studied, which makes it possible to obtain larvae from artificially fertilized eggs of this mollusc species in controlled laboratory conditions. In this work, the fatty acid composition of <i>M. galloprovincialis</i> larvae at the trochophore stage on the 3<sup>rd</sup> day in the control experiment and under artificial contamination with polychlorinated biphenyls (PCBs) in different concentrations is studied for the first time. The fatty acid composition of total lipids in the biomass of larvae obtained on the 3<sup>rd</sup> day of the experiment was studied by means of gas chromatography - mass spectrometry. Totally, 14 fatty acids were identified in the samples; 59 % of them were saturated fatty acids, 24 % were monounsaturated fatty acids, and 17 % were polyunsaturated fatty acids. Statistical analysis was performed using Statistical Toolbox of MATLAB software (version 8.2). The totals of monounsaturated and polyunsaturated fatty acids significantly differed in lipids of <i>M. galloprovincialis</i> trochophores in the experiment with different PCB concentrations. The totals of saturated fatty acids did not significantly differ. The major saturated fatty acids in all mussel trochophores studied were palmitic (C16:0) and stearic (C18:0) acids. Their concentration did not significantly change under the exposure to PCBs. The main monounsaturated fatty acids were oleic (C18:1ω9), palmitoleic (C16:1ω7), and vaccenic (C18:1ω7) acids. The fraction of monounsaturated fatty acids was twice as low when exposed to the PCB concentrations 0.1 and 1.0 μg·L<sup>-1</sup>. However, when the PCB concentration was 10 μg·L<sup>-1</sup>, the total of these acids did not differ from the control. Among polyunsaturated fatty acids having biological essentiality, it was possible to identify arachidonic (C20:4ω6), eicosapentaenoic (C20:5ω3), and docosahexaenoic (C22:6ω3) acids. The total fraction of omega-3 and omega-6 acids in mussel larvae in the control did not exceed 12.8 %. With an increase of the PCB concentration in the growth medium 0.1 to 1.0 μg·L<sup>-1</sup>, the fraction of polyunsaturated fatty acids increased 2.5-fold. At the PCB concentration 10 μg·L<sup>-1</sup> and in the sample with pure acetone added, the total fraction of polyunsaturated fatty acids was comparable with that in the control. The results of the study indicate that fatty acid response is the highest when the medium is exposed to the PCB concentrations ranging 0.1 to 1.0 μg·L<sup>-1</sup>. At the PCB concentrations equal to 10 μg·L<sup>-1</sup> or higher, biochemical processes in larvae seem to slow down. The results of this study will contribute to a better understanding of biochemical rearrangements that allow molluscs at larval developmental stages to adapt to environmental pollution with organic xenobiotics.