Long-chain (≥ C₂₀) polyunsaturated fatty acids (LC-PUFA), such as eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), are necessary for human health and are obtained from marine fish-derived oils. Marine fish are LC-PUFA-rich animals; however, many of them require LC-PUFA for growth. Therefore, it is suggested that they do not have sufficient ability to biosynthesize LC-PUFA. To evaluate in vivo LC-PUFA synthetic activity in fish cells, fish-derived cell lines from red sea bream (Pagrus major, PMS and PMF), Japanese flounder (Paralichthys olivaceus, HINAE), and zebrafish (Danio rerio, BRF41) were incubated with n-3 fatty acids labeled by radioisotopes or stable isotopes, and then, n-3 PUFA were analyzed by thin-layer chromatography or liquid chromatography-mass spectrometry. Labeled EPA and DHA were biosynthesized from labeled α-linolenic acid (18:3n-3) in BRF41, whereas they were not detected in PMS, PMF, or HINAE cells. We next cloned the fatty acid desaturase 2 (Fads2) cDNAs from PMF cells and zebrafish, expressed in budding yeasts, and then analyzed the substrate specificities of enzymes. As a result, we found that Fads2 from PMF cells was a ∆6/∆8 desaturase. Collectively, our study indicates that cell lines from red sea bream and Japanese flounder were not able to synthesize EPA or DHA by themselves, possibly due to the lack of ∆5 desaturase activity. Furthermore, this study provides a sensitive and reproducible non-radioactive method for evaluating LC-PUFA synthesis in fish cells using a stable isotope and liquid chromatography-mass spectrometry.

长链 (≥ C ₂₀ ) 多不饱和脂肪酸 (LC-PUFA)，例如二十碳五烯酸 (20:5n-3, EPA) 和二十二碳六烯酸 (22:6n-3, DHA)，对人体健康是必需的，并且是从海洋鱼油中提取。海鱼是富含 LC-PUFA 的动物；然而，它们中的许多需要 LC-PUFA 才能生长。因此，表明它们没有足够的生物合成 LC-PUFA 的能力。评估鱼细胞、来自红鲷（Pagrus major、PMS 和 PMF）、日本比目鱼（Paralichthys olivaceus、HINAE）和斑马鱼（Danio rerio）的鱼源细胞系的体内 LC-PUFA 合成活性, BRF41) 与放射性同位素或稳定同位素标记的 n-3 脂肪酸一起孵育，然后通过薄层色谱法或液相色谱-质谱法分析 n-3 PUFA。标记的 EPA 和 DHA 在 BRF41 中由标记的 α-亚麻酸 (18:3n-3) 生物合成，而在 PMS、PMF 或 HINAE 细胞中未检测到它们。我们接下来克隆了来自 PMF 细胞和斑马鱼的脂肪酸去饱和酶 2 (Fads2) cDNA，在芽殖酵母中表达，然后分析了酶的底物特异性。结果，我们发现来自 PMF 细胞的 Fads2 是一种 ∆6/∆8 去饱和酶。总的来说，我们的研究表明，来自红鲷和日本比目鱼的细胞系无法自行合成 EPA 或 DHA，这可能是由于缺乏 Δ5 去饱和酶活性。此外，