Laboratorio de Acuicultura, Instituto de Investigaciones Agropecuarias y Forestales, UMSNH, Av. San Juanito Itzícuaro S/N, Col. San Juanito Itzícuaro, C.P. 58330, Morelia, Michoacán, Mexico.
Departamento de Biología Animal (U.D.I. Fisiología Animal), Facultad de Biología, Universidad de La Laguna, La Laguna, Tenerife, Spain.
Fish Physiol Biochem. 2012 Aug;38(4):1047-1057. doi: 10.1007/s10695-011-9589-6. Epub 2012 Jan 15.
The genus Chirostoma (silversides) belongs to the family Atherinopsidae, which contains around 150 species, most of which are marine. However, Mexican silverside (Chirostoma estor) is one of the few representatives of freshwater atherinopsids and is only found in some lakes of the Mexican Central Plateau. However, studies have shown that C. estor has improved survival, growth, and development when cultured in water conditions with increased salinity. In addition, C. estor displays an unusual fatty acid composition for a freshwater fish with high docosahexaenoic acid (DHA)/ eicosapentaenoic acid (EPA) ratios. Freshwater and marine fish species display very different essential fatty acid metabolism and requirements, and so the present study investigated long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis to determine the capacity of C. estor for endogenous production of EPA and DHA, and the effect that salinity has on these pathways. Briefly, C. estor were maintained at three salinities (0, 5, and 15 ppt), and the metabolism of ¹⁴C-labeled 18:3n-3 was determined in isolated hepatocyte and enterocyte cells. The results showed that C. estor has the capacity for endogenous biosynthesis of LC-PUFA from 18-carbon fatty acid precursors, but that the pathway was essentially only active in saline conditions with virtually no activity in cells isolated from fish grown in freshwater. The activity of the LC-PUFA biosynthesis pathway was also higher in cells isolated from fish at 15 ppt compared with fish at 5 ppt. The activity was around fivefold higher in hepatocytes compared with enterocytes; although the majority of 18:3n-3 was converted to 18:4n-3 and 20:4n-3 in hepatocytes, the proportions of 18:3n-3 converted to EPA and DHA were higher in enterocytes. The data were consistent with the hypothesis that conversion of EPA to DHA could contribute, at least in part, to the generally high DHA/EPA ratios observed in the tissue lipids of C. estor.
银汉鱼属（银汉鱼）属于银汉鱼科，该科约有 150 种，其中大部分为海洋物种。然而，墨西哥银汉鱼（Chirostoma estor）是为数不多的淡水银汉鱼代表之一，仅分布在墨西哥高原的一些湖泊中。然而，研究表明，当在盐度增加的水条件下培养时，C. estor 的存活率、生长和发育得到了提高。此外，C. estor 的脂肪酸组成对于淡水鱼来说非常不寻常，其二十二碳六烯酸（DHA）/二十碳五烯酸（EPA）比值较高。淡水和海洋鱼类的必需脂肪酸代谢和需求有很大差异，因此本研究调查了长链多不饱和脂肪酸（LC-PUFA）的生物合成，以确定 C. estor 内源性产生 EPA 和 DHA 的能力，以及盐度对这些途径的影响。简而言之，将 C. estor 维持在三个盐度（0、5 和 15 ppt）下，并在分离的肝细胞和肠细胞中测定 ¹⁴C 标记的 18:3n-3 的代谢。结果表明，C. estor 具有从 18 碳脂肪酸前体内源合成 LC-PUFA 的能力，但该途径基本上仅在盐度条件下活跃，在从淡水生长的鱼类中分离的细胞中几乎没有活性。在 15 ppt 下生长的鱼类的 LC-PUFA 生物合成途径的活性也高于在 5 ppt 下生长的鱼类。该活性在肝细胞中比肠细胞中高约五倍；尽管 18:3n-3 主要转化为 18:4n-3 和 20:4n-3，但肠细胞中 18:3n-3 转化为 EPA 和 DHA 的比例较高。这些数据与这样的假设一致，即 EPA 向 DHA 的转化至少部分有助于 C. estor 组织脂质中普遍较高的 DHA/EPA 比值。
