The rabbitfish Siganus canaliculatus was the first marine teleost reported to possess long-chain polyunsaturated fatty acid (LC-PUFA) biosynthetic ability, and the related molecular mechanisms have been well clarified. Here, we investigated the LC-PUFA biosynthesis capability of the congeneric rabbitfish S. guttatus. First, cDNAs of genes for four key enzymes related to LC-PUFA biosynthesis, namely Δ6Δ5 fatty acyl desaturase (fads2) (1335 bp; 445 aa), Δ4 fads2 (1335 bp; 445 aa), and elongation of very long chain fatty acid proteins (elovl5) (873 bp; 291 aa) and elovl4 (906 bp; 302 aa) were cloned from the liver of S. guttatus. The Δ6Δ5 fads2, Δ4 fads2 and elovl5 genes showed high expression in brain, liver, spleen, gallbladder, and intestine but relatively low expression in eye, whereas the elovl4 gene showed specific and high expression in eye. During embryogenesis, mRNA expression of Δ4 fads2 and elovl4 was detected from 8 h post-fertilization (hpf) and then maintained a high level to 24 hpf, while mRNA expression of Δ6Δ5 fads2 and elovl5 reached a peak at 14 hpf but then declined. In addition, ambient salinity (32 ppt and 20 ppt) exerted some regulatory influence on the expression of the four genes during embryogenesis. The levels of C18 PUFA precursors and, especially, PUFA and DHA of the embryos, decreased from 17 hpf to 24 hpf. These results suggested that S. guttatus, similar to the congeneric S. canaliculatus, would have capability for LC-PUFA biosynthesis, which is still not activated at the fertilized egg stage.

兔鱼Siganus canaliculatus是第一个被报道具有长链多不饱和脂肪酸（LC-PUFA）生物合成能力的海洋硬骨鱼，相关分子机制已得到很好的阐明。在这里，我们研究了同属兔鱼S. guttatus的 LC-PUFA 生物合成能力。首先，与LC-PUFA生物合成相关的四种关键酶基因的cDNA，即Δ6Δ5脂肪酰基去饱和酶（fads 2）（1335 bp; 445 aa）、Δ4 fads 2（1335 bp; 445 aa）和超长链延长从S. guttatus的肝脏中克隆了脂肪酸蛋白 ( elovl 5) (873 bp; 291 aa) 和elovl 4 (906 bp; 302 aa) 。Δ6Δ5 fads 2、Δ4 fads 2 和elovl 5 基因在脑、肝、脾、胆囊和肠中高表达，但在眼中表达相对较低，而elovl 4 基因在眼中表现出特异性和高表达。在胚胎发生过程中，Δ4 fads 2 和elovl 4 的 mRNA 表达从受精后 8 h 开始检测到，然后维持高水平至 24 hpf，而 Δ6Δ5 fads 2 和elovl 5 的 mRNA 表达在 14 hpf 时达到峰值，但然后拒绝了。此外，环境盐度（32 ppt和20 ppt）对胚胎发生过程中四个基因的表达产生一定的调节影响。胚胎的 C18 PUFA 前体，特别是 PUFA 和 DHA 的水平从 17 hpf 下降到 24 hpf。这些结果表明，与同属S. canaliculatus类似， S. guttatus具有LC-PUFA 生物合成能力，但在受精卵阶段尚未激活。