Optimization of an analytical methodology to study heat shock influence on the fatty acid composition of the gills of the Antarctic fish Trematomus bernacchii.

In the Ross Sea region, Antarctica (average temperature of -1.87 °C), shelf water warming up to +0.8-+1.4 °C is predicted by 2200 [1], so there is a great concern to understand how organisms can respond to rising temperatures. In this study, we analysed the effect of a thermal shock on the fatty acid (FAs) composition of the gills of the Antarctic notothenioid Trematomus bernacchii. In order to analyze the fatty acid composition in gills, we further optimized an analytical method already successfully applied to muscle tissue of fish [2,3]. This method is based on a fast microwave-assisted extraction (MAE) of lipids from a lyophilized sample, a base-catalyzed trans-esterification of lipid extract to obtain Fatty Acids Methyl Esters, and their separation and identification by gas chromatography-mass spectrometry. MAE for the extraction of lipids from tissues has received a growing interest as it allows a minimum sample handling and a fast extraction that exposes the sample to relatively high temperatures for a very short time. The total lipid percentage in gills of T. bernacchii was 0.6±0.3% ww (wet weight): these data are among the first ever published for this species. Specimens, caught in Terra Nova Bay (Ross Sea) during the austral Summer 2014-15, were held in fish tanks at 0, +1 or +2 °C, for 1, 5 and 10 days. In general, thermal shock produced an alteration in total lipid content, with a statistically significant increase only after 10 days of exposure at high temperatures, respect to specimens held in tanks at -1.8 °C and used as control group. Moreover, a general increase in the percentage of total saturated, and a decrease in mono-unsaturated FAs was evidenced for all groups, whereas total polyunsaturated FAs increased in specimen exposed at 0 and +1 °C, and decreased in those held in tanks at +2 °C. Principal component analysis indicated that both temperature and exposure time affected the composition of FAs in the gills, also if in different way respect to the FA composition of muscle of specimens used in the same experiment [4]. This study demonstrates that T. bernacchii was capable to rapidly acclimatize to a thermal shock, and contributes to increasing knowledge on the effect of temperature on Antarctic notothenioids, being complementary to previous studies on the gene expression and biochemistry of this species face multiple stressors.