Effect of dietary krill oil levels on the regulation of ovary development in Pacific white shrimp (Litopenaeus vannamei) broodstock

Krill oil is rich in phospholipids and has been proven to significantly promote ovarian development in shrimp. However, the optimal level and related mechanism are unknown. In this study, four isonitrogenous and isolipidic diets were prepared. These diets included different gradients of krill oil supplementation (3%, 6%, and 9%), with no-krill oil serving as a control. Female Litopenaeus vannamei broodstock with stage I ovarian development were fed these diets for 28 days. The results showed that the inclusion of krill oil in the diet had a positive effect on ovarian development in female shrimp, particularly at the 6% supplementation level. This was evident from the significant improvements in the gonadosomatic index and in the 17β-estradiol, progesterone, and methyl farnesoid levels. Moreover, 6% krill oil supplementation facilitated lipid accumulation in the hepatopancreas, promoted the deposition of yolk granules within the oocyte, and significantly enhanced the mobilization efficiency of triglycerides and total cholesterol from the hepatopancreas to the ovary. The upregulation of the serum metabolites choline and phosphorylcholine promotes the synthesis of phosphatidylcholine and triglycerides. Additionally, prostaglandin E₂ stimulates the production of ovarian steroid hormones. Acamprosate influences the activity of glutamic acid, potentially leading to a reduction in the secretion of gonadal inhibitory hormones. Multiomics analysis revealed joint enrichment of differentially altered metabolites and differentially expressed genes in pathways involved in arachidonic acid metabolism, cholesterol metabolism, and ovarian steroid synthesis. Additionally, there was significant enrichment in glycerophospholipid metabolism. The expression of the cytosolic phospholipase A₂ gene was upregulated in both the lipid metabolism and steroid synthesis pathways. Moreover, the mRNA expression levels of 3β-hydroxysteroid dehydrogenase/delta 5- > 4-isomeras, cytochrome P450 2 L1, and prostaglandin H synthase 2 were also upregulated in the ovarian steroid synthesis pathway. In conclusion, supplementing the diet with 6% krill oil is optimal for promoting lipid metabolism and steroid hormone secretion in female L. vannamei broodstock, thereby enhancing ovarian development and maturation.