Fatty acid composition and gene expression in the third generation of Atlantic salmon families selected for high and low capacity of omega3 fatty acid synthesis

The major aim of this thesis was to study offspring (the third generation) of Atlantic salmon selected by high and low EPA and DHA synthesis capacity (according to high and low d6dB expression level in liver) have differences in total fat content and fatty acid composition, and also difference in gene expression of genes related to n-3 HUFA synthesis pathway in tissues (liver, intestine and muscle). The total fat contents in each tissue were analyzed by Folch method and showed no significant difference between two genetic groups. Fatty acid composition was analyzed by GC with methylation method. Liver plus group (offspring of high EPA and DHA synthesis capacity parents) showed significantly higher percentage of EPA+DHA than liver minus group (offspring of low EPA and DHA synthesis capacity parents) and also higher than intestine and muscle. In muscle and intestine, there was no significant difference of EPA+DHA percentage between two genetic groups. The gene expression was analyzed by qPCR and the relative expression ratio was calculated by method. elovl5a was higher in liver plus group, elovl2 and d6dA were higher in intestine minus group. Except elovl5a, elovl2 and d6dA, other genes (include d6dB) were with no significant differences between genetic groups in all tissues. The present study has shown EPA and DHA synthesis capacity in liver was improved by gene selective breeding, but EPA and DHA deposition in flesh was not improved by this capacity when salmon fed marine diet. The muscle fatty acid composition is more likely depended on diet composition. Thus, further studies can focus on dietary effects on EPA and DHA synthesis and deposition capacity of fish selected by high and low EPA and DHA synthesis capacity.M-F