Vitamin D impacts on the intestinal health, immune status and metabolism in turbot (Scophthalmus maximus L.)

Abstract

Vitamin D (VD) plays a vital role in various physiological processes in addition to its classic functions on maintaining the balance of calcium and phosphorus metabolism. However, there still are gaps to understand in depth the issues on the precise requirement, metabolic processes, and physiological functions of VD in fish. In this study, we investigated the effects of VD on the growth, intestinal health, host immunity and metabolism in turbot (Scophthalmus maximus L.), one important commercial carnivorous fish in aquaculture, through the supplementation of different doses of dietary VD3 (0, 200, 400, 800 and 1600 IU VD3/kg diet). According to our results, the optimal VD3 level in the feed for turbot growth was estimated to be around 400 IU/kg, whereas VD3 deficiency or overdose in diets induced the intestinal inflammation, lowered the diversity of gut microbiota, and impaired the host resistance to bacterial infection in turbot. Moreover, the level of 1α,25(OH)2D3, the active metabolite of VD3, reached a peak value in the turbot serum in the 400 IU group, although the concentrations of calcium and phosphate in the turbot were stable in all groups. Finally, the deficiency of dietary VD3 disturbed the nutritional metabolism in turbot, especially the metabolism of lipids and glucose. In conclusion, this study evaluated the optimal dose of dietary VD3 for turbot, and provided the evidence that VD has a significant impact on intestinal health, host immunity and nutritional metabolism in fish, which deepened our understanding on the physiological functions and metabolism of VD3 in fish.

Vitamin D regulates insulin pathway and glucose metabolism in zebrafish ( Danio rerio )

“…Previous results both from others and from our research group have demonstrated that VD 3 significantly impacts the glucose metabolism in higher animals 17 and fish 28 . It is well‐known that insulin is one of the most important hormones to maintain glucose homeostasis 29 .…”

“…More importantly, our results have demonstrated Previous results both from others and from our research group have demonstrated that VD 3 significantly impacts the glucose metabolism in higher animals 17 and fish. 28 It is well-known that insulin is one of the most important hormones to maintain glucose homeostasis. 29 Meanwhile, insr is a key element in insulin signaling pathway, and insulin/insr interaction serves to amplify and diversify insulin actions.…”

Physiological function of vitamin D3 in fish

“…Possible reasons for the discrepancy in C proteins across studies may be as follows: First, the settings of the control groups in each study are not uniform (generally, the control group is VD 3 deficiency or the minimum demand of VD 3 in this species). If the controls are VD 3 deficient, it may cause more serious inflammation in the fish body 51,66 . Second, fish C protein gene is not only expressed in the liver, but also in brain, intestine, kidney, gill, skin, gonad and other organs, and participates in the body fluid, lymph and blood circulation 93 .…”

“…According to Darias et al, dietary VD 3 can promote the maturation of the intestinal digestive function of European sea bass and enhance the activity of digestive enzymes 82 . A new study showed that dietary VD 3 deficiency decreased the gut microbial population of turbot, while the abundance of beneficial bacteria such as Lactobacilli increased in the VD 3 ‐sufficient group 66 …”

“…Taveekijakarn et al found that salmon ( Oncorhynchus keta ) fed with the diet free of VD 3 developed epidermis thinning and extensive necrotisation of the underlying musculature and hypocalcaemia 120 ; however, the pathological changes were reversed when the same fish were fed a VD 3 supplemented diet after the deficiency period. Dietary VD 3 deficiency has also been associated with decreased immune function in Asian swamp eel, 51 as well as high incidence of intestinal inflammation, decreased abundance of intestinal flora and weakened antibacterial ability of turbot 66 . On the other hand, fish appear to be very tolerant to high concentrations of VD 3 in their diet; most studies have not reported negative outcomes associated with high dietary concentrations of VD 3 .…”