Effect of dietary HUFA on reproductive performance, tissue fatty acid profile and desaturase and elongase mRNAs in female swordtail Xiphophorus helleri

Freshwater fish species possess higher capability to utilize plant based oils as dietary lipid source due to their ability to biosynthesize highly unsaturated fatty acids (HUFA) to meet requirements needed for growth and development. However, there is paucity in knowledge on the requirement for dietary HUFA in freshwater broodstock during active spawning stage. We conducted a study on the effect of different levels of dietary HUFA on fry production, tissue fatty acid profiles and mRNAs expression of desaturase and elongase genes in female swordtail (Xiphophorus helleri), a freshwater viviparous poeciliid. Three isonitrogenous experimental diets utilizing different ratio of squid oil and linseed oil (100% squid oil, 1:1 squid oil:linseed oil and 100% linseed oil) as lipid source were formulated and fed to female swordtails for 26 weeks. Spawning was carried out every 30 days. Results showed that diet containing mixture of squid and linseed oil as lipid sources (dietary n-3 HUFA 2.2% dry matter) resulted in significantly highest number of fry production. In general, fatty acid profiles of liver, muscle and oocyte reflected profiles of respected experimental diets. Utilization of linseed oil as sole lipid source significantly lowered deposition of docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (ARA, 20:4n-6) in all three tissues, which probably affected reproduction performance. Deposition pattern of ARA in oocyte and fry also indicated the importance of this fatty acid in swordtail reproductive activities. Our results also showed increased expression of desaturase mRNA with increasing levels of dietary linseed oil in liver and muscle. This is also observed in hepatic and muscle elongase expression patterns. We also showed for the first time, regulation of desaturase transcriptional expression in ovary by dietary fatty acid profile. There was however no clear pattern in ovary elongase expression between the three diets. Collectively, this study showed that female swordtail benefits from inclusion of dietary HUFA during reproductive stages, despite possessing the ability to increase transcription of desaturase and elongase during low dietary HUFA provision. However, excessive dietary HUFA could result in imbalanced ratios of HUFA, which could impair reproductive processes.