Retention of Fillet Coloration in Rainbow Trout After Dietary Astaxanthin Cessation

This study was conducted to determine the retention time of rainbow trout (Oncorhynchus mykiss) fillet coloration, as indicated by hue, chroma, and entire color index (ECI) values, after the cessation of dietary astaxanthin. After 12 weeks of receiving a diet containing astaxanthin, rainbow trout [mean (SD) length 240 (26) mm, weight 194 (65) g] were either switched to a non-astaxanthin diet or continued to receive the same astaxanthin diet for 55 d. In addition, a control group was fed a non-astaxanthin diet for the entire duration of the study. Digital coloration measurements (L*, a*, and b*) were recorded on fillets and used to calculate hue, chroma, and ECI values. Hue, chroma, and ECI did not significantly change within any of the treatments over the course of the study. Hue, chroma, and ECI were also not significantly different between the fillets of those fish that either continued to receive astaxanthin-supplemented feed compared to those that were switched from an astaxanthin diet to diet free of astaxanthin. However, ECI, hue, and chroma were significantly different in fillets from the fish that had never received dietary astaxanthin compared to fillets from the other two treatments. These results indicate that catchable-sized rainbow trout stocked into recreational fishing waters with minimal natural feed should retain fillet coloration for at least 55 d after stocking, making astaxanthin supplementation in recreational hatcheries a viable tool to improve angler satisfaction.