Dietary Vitamin D3 Supplementation Enhances Fillet Vitamin D Content in Rainbow Trout

Farmed salmonids are an important dietary source of vitamin D for consumers, yet their vitamin D content varies significantly depending on feed formulation. Regulatory changes in the EU, have raised the maximum permissible vitamin D3 levels in fish feed, prompting interest in understanding its transfer efficiency from feed to fillet. 

This study explored how different levels of synthetic vitamin D3 (cholecalciferol) supplementation influence whole body and fillet vitamin D3 deposition in rainbow trout reared under recirculating aquaculture system (RAS) conditions. The research was conducted by BioMar’s R&D team in Denmark between July and September 2022, over a 61-day feeding period. Ten dietary treatments were tested with increasing levels of synthetic vitamin D3, ranging from 8,100 to 77,400 IU/kg feed. Fish performance parameters, nutrient retention, and fillet pigmentation were assessed to determine safety, efficacy, and potential nutritional benefits. 

Results 

Growth Performance 

The study found that increasing dietary vitamin D3 levels did not affect growth performance, including feed intake, specific growth rate, or feed conversion ratio. This confirms that vitamin D3 supplementation is safe at the tested levels. 

Vitamin D3 Deposition 

Although growth was unaffected, vitamin D3 supplementation significantly improved vitamin D3 deposition. Fillet vitamin D3 content increased proportionally with dietary levels, supporting targeted enrichment strategies to enhance the nutritional value of the final fish product for consumers. ##### Pigmentation and Fillet Quality 

Fillet pigmentation, as measured by MINOLTA a* values, increased linearly with higher dietary vitamin D3 supplementation levels, indicating a potential improvement in fillet redness, although this effect was not statistically significant. Overall, vitamin D3 supplementation maintained fillet appearance while supporting enrichment strategies. 

These findings demonstrate that farmed rainbow trout fillets can be effectively enriched with vitamin D3 through feed formulation without compromising growth or feed efficiency. From a consumer perspective, this enhances the nutritional value of farmed fish, addressing widespread dietary vitamin D deficiencies in human populations. The study highlight that targeted vitamin D3 supplementation in trout feeds improves fillet nutritional quality while maintaining production performance. As consumer focus grows on nutritional fortification and sustainable aquaculture practices, optimizing feed formulations for micronutrient enrichment will support market differentiation and public health goals.