Influence of dietary HUFA levels on reproductive performance, tissue fatty acid profile and desaturase and elongase mRNAs expression in female zebrafish Danio rerio

We conducted a study to investigate the effect of different levels of dietary highly unsaturated fatty acids (HUFAs) on tissue fatty acid profiles and reproductive performance in female zebrafish. In addition, the mRNA expression of desaturase and elongase genes in liver, muscle and ovarian tissues were also analysed. Three iso-nitrogenous experimental diets utilizing different ratios of squid oil and linseed oil which were SO (100% squid oil), SLO (1:1 squid oil:linseed oil) and LO (100% linseed oil) as lipid sources were formulated and fed to female zebrafish for 12 weeks. Spawning was carried out twice weekly during the experimental feeding period. Results showed that fatty acid profiles of liver, muscle, ovary and egg reflected profiles of the corresponding dietary treatment. In general, increasing levels of dietary linseed oil lowered deposition of docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (ARA, 20:4n-6) in all tissues. Liver fatty acid profile implied increasing biosynthesis activities during feeding of low dietary HUFA diets, which was supported by increased expression of hepatic desaturase and elongase mRNAs. However, the increased HUFA biosynthesis activities were unable to compensate for the inferior hepatic ARA, EPA and DHA levels of fish fed diet LO. In muscle and ovary tissues, relatively lower concentrations of ARA and EPA were also obtained with diet LO. There was no significant difference in EPA and ARA levels in eggs, which imply accumulation of EPA and ARA in eggs. We also showed an increasing trend of ovarian desaturase and elongase gene expression during low dietary HUFA levels. Highest egg production and hatching rate was obtained with diet SLO, which strongly suggests the need for both inclusion and balanced ratio of dietary n-3 and n-6 unsaturated fatty acids by spawning females. Collectively, this study shows that female zebrafish reproduction benefits from the supply of dietary HUFA during reproductive stages, despite possessing ability to increase transcription of desaturase and elongase in various tissues during low dietary HUFA intake.