Unravelling the enigmatic vitamin D production in the sea

The origin of vitamin D in human and mammals ie. production of vitamin D in the skin by UVBexposure and vitamin D in the diet is well documented, but this is not the case for fish, despite the fact that both fatty and lean fish are good sources for vitamin D. Currently, phyto and zoo plankton are regarded as the vitamin D source for fish, but research data do not fully support this assumption. Moreover, fish skin contains the precursor to vitamin D and formation of vitamin D in fish has been demonstrated, but considered insignificant 25 years ago. Interestingly, it has recently been shown that rainbow trout forms vitamin D from blue light which penetrate far deeper. We aim to understand the origin of vitamin D in the sea by quantifying vitamin D in phyto- and zooplankton, small fish, in fish skin exposed with light waves from UVB to blue light, and finally elucidate the physiochemical mechanism for fish skin production of vitamin D.

vitamin D; fish, sea

Knowledge of the origin of vitamin D for humans and mammals is well documented. We get vitamin D via the sun's UVB rays and through vitamin D in our diet, where diet is the most important source during the winter. Fatty as well as lean fish generally have a high content of vitamin D. Fatty fish, included in
the official dietary advice, as a good source of vitamin D, but a lean fish like halibut actually has a higher vitamin D content than farmed salmon. Vitamin D in farmed salmon is through many years reported lower than in wild salmon, and exceptionally low for salmon reared in systems on land. The general view is that fish get their vitamin D through food. Fish skin contains the precursor to vitamin D, just like in humans, and vitamin D can be formed in fish by UVB illumination,
but was assessed as insignificant 25 years ago, as UVB light does not penetrate far into the sea. Recently, it has been shown that rainbow trout formed vitamin D when exposed to blue light. We will investigate the origin of vitamin D in the sea by determining the content of vitamin D in phyto- and zoo-plankton, in small fish, in fish skin illuminated with UVB- to blue light, and describe the background for the difference between fish skin and our skin for the formation of vitamin D. The purpose of our project is to create the basis for the future layout of facilities for farmed fish. An adaptation that can result in a better end product, a better performance and thus better earnings for the breeder and lower emissions to the environment.