“Color of aquarium fishes has an important role in preference of consumers. Insufficient coloration reduces economical value and not meet consumer demands both.”
“The study showed that tomato powder as being natural carotenoid source was not found to be affective on the fish skin pigmentation.”
The paper : Investigation of the Effect of Tomato Powders as a Dietary Supplement on Skin Pigmentation of Goldfish was presented at the 2012 International Conference of Agricultural Engineering (CIGR-Ageng2012), Valencia, Spain. (motto : “Agriculture & Engineering for a Healthier Life”
Thanks to Heptagon @ Wikipedia for providing a tweakable goldfish photo.