<p>Flesh colour is a critical quality criterion for consumer purchasing of salmonid products. As fish cannot synthesize pigments endogenously, they must be provided in their diet, and in Atlantic salmon farming, synthetic astaxanthin is the most widely used dietary supplement. This study evaluated two astaxanthin products derived from the microalga <i>Haematococcus lacustris</i> against a commercial synthetic product. Seven dietary treatments were tested in duplicate tanks using Atlantic salmon reared in a commercial freshwater recirculation system. Diets included: a negative control with no astaxanthin (C); two synthetic astaxanthin positive control treatments at 40 and 80&#xa0;mg Ax [kg diet]⁻¹, Low and High, respectively; and two natural astaxanthin products, oleoresin (O) and powder (P), each at the same two concentrations. Fish were assessed monthly for production parameters, and after six months, ten fish per tank were sampled for further analyses. Diet significantly influenced fillet pigmentation and tissue astaxanthin content, while most production parameters, biological indices, fillet proximate composition, structural parameters, and shelf life were not significantly affected. Initial fish size and stocking density significantly influenced several response variables. Oleoresin resulted in fillet pigmentation comparable to the synthetic product and superior to the powder product, indicating that it has strong potential as a natural alternative to synthetic astaxanthin in Atlantic salmon farming.</p>