Krill oil: A high quality phospholipid source for ovary development of female red claw crayfish, Cherax quadricarinatus

Three isonitrogenous and isolipidic experimental diets (2% supplement with soy lecithin, egg yolk lecithin, or krill oil) and one control diet (without phospholipid supplement) were formulated for female red claw crayfish Cherax quadricarinatus for 10 weeks. Results indicated that phospholipid supplement can improve gonadosomatic index, especially in krill oil diet treatment. C. quadricarinatus fed diet with soybean lecithin showed the highest hepatosomatic index. Krill oil diet is more effective than soy lecithin and egg yolk lecithin diets in promoting hepatosomatic and ovarian lipid deposition (including total cholesterol and triglyceride). Krill oil in diet also can improve the accumulation of yolk granule and increase the ratio and diameter of marine oocytes. Supplement with phospholipid increased the serum high-density lipoprotein concentration and ovarian methyl farnesoate, estradiol and progesterone contents, especially in crayfish fed with krill oil diet. Low-density lipoprotein in serum and gonadal inhibitory hormone and molting inhibitory hormone concentration in eyestalks were all decreased significantly in crayfish when fed diets with phospholipid supplement. Furthermore, crayfish fed diet with krill oil showed significantly lower malondialdehyde content and higher specific activities of superoxide dismutase, a total antioxidant enzyme, and glutathione peroxidase in hepatopancreas than other experimental treatments. Ovarian lipidomics results indicated that phosphatidylcholine and phosphatidylethanolamine are two primary lipid molecules response to dietary phospholipid. Among these lipids, long chain polyunsaturated fatty acids were important participants in ovarian development of crayfish. Combined transcriptome and lipidomics analysis showed that krill oil diet can improved ovarian development of C. quadricarinatus by improve related gene expressions of steroid hormone biosynthesis, sphingolipid signaling pathway, retinol metabolism, regulation of lipolysis in adipocytes and pancreatic secretion. Therefore, krill oil can be an excellent phospholipid source for C. quadricarinatus adult at the stage of gonadal development.

本实验为红螯螯虾（Cherax quadricarinatus）雌性成体配制了4组等氮等脂饲料，包括1组无磷脂添加的基础对照饲料，以及3组分别添加2%大豆卵磷脂、蛋黄卵磷脂或南极磷虾油的实验饲料，养殖周期为10周。实验结果表明，饲料中添加磷脂可提升红螯螯虾的性腺指数，其中南极磷虾油组的提升效果最为显著。摄食大豆卵磷脂饲料的螯虾肝体指数最高。在促进肝组织与卵巢脂质沉积（包括总胆固醇与甘油三酯积累）方面，南极磷虾油组的效果优于大豆卵磷脂组与蛋黄卵磷脂组。此外，南极磷虾油组还可促进卵黄颗粒积累，提升卵母细胞的比例与直径。饲料添加磷脂可提高血清高密度脂蛋白浓度，以及卵巢中法尼酸甲酯、雌二醇与孕酮的含量，其中南极磷虾油组的提升效果最为突出。摄食添加磷脂饲料的螯虾，其血清低密度脂蛋白、眼柄中的性腺抑制激素与蜕皮抑制激素浓度均显著降低。进一步分析显示，与其余实验组相比，摄食南极磷虾油饲料的螯虾肝胰腺中丙二醛含量显著更低，而超氧化物歧化酶、总抗氧化酶及谷胱甘肽过氧化物酶的比活力显著更高。卵巢脂质组学分析结果显示，磷脂酰胆碱与磷脂酰乙醇胺是响应饲料磷脂添加的两类主要脂质分子；其中长链多不饱和脂肪酸在螯虾卵巢发育过程中发挥重要作用。联合转录组与脂质组学分析表明，南极磷虾油饲料可通过调控类固醇激素生物合成、鞘脂信号通路、视黄醇代谢、脂肪细胞脂解调控及胰腺分泌相关基因的表达，促进红螯螯虾的卵巢发育。因此，南极磷虾油可作为红螯螯虾性腺发育阶段成体的优质磷脂源。