Effects of the Interaction between Dietary Vitamin D3 and Vitamin K3 on Growth, Skeletal Anomalies, and Expression of Bone and Calcium Metabolism-Related Genes in Juvenile Gilthead Seabream (Sparus aurata)

The interaction between vitamin D and vitamin K is crucial for regulating bone metabolism and maintaining calcium homeostasis across diverse animal species due to their complementary roles in calcium metabolism and bone health. However, research on this interaction of vitamin D and K in fish, particularly Mediterranean species like gilthead seabream, is limited or not studied. This study aimed to understand the effects of different dietary combinations of vitamin D₃ and K₃ on juvenile gilthead seabream. Accordingly, seabream juveniles were fed with varying combinations of vitamin D₃/vitamin K₃ (mg/kg diet) for 3 months: (0.07/0.01), (0.20/0.58), (0.19/1.65), (0.51/0.74), (0.56/1.00). At the end of the trial, survival, growth, body morphology, serum calcitriol, and vertebral mineral composition remained unaffected by varying vitamin levels, while gene expression patterns related to bone formation, resorption, and calcium regulation in various tissues were significantly influenced by both vitamins and their interaction. Gilthead seabream juveniles fed the 0.07/0.01 mg/kg diet upregulated calcium-regulating genes in the gills, indicating an effort to enhance calcium absorption to compensate for dietary deficiencies. Conversely, an increase in vitamin D₃ and K₃ up to 0.19 and 1.65 mg/kg, respectively, upregulated bone formation, bone remodeling, and calcium homeostasis-related gene expression in vertebra and other tissues. On the contrary, a dietary increase in these vitamins up to 0.56 mg/kg vitamin D₃ and 1.00 mg/kg vitamin K₃ downregulated calcium metabolism-related genes in tissues, suggesting an adverse interaction resulting from elevated levels of these vitamins in the diet. Hence, sustaining an equilibrium in the dietary intake of vitamin D₃ and vitamin K₃, in an appropriately combined form, may potentially induce interactions between the vitamins, contributing to favorable effects on bone development and calcium regulation in gilthead seabream juveniles.