Color-Enhancing Fish Foods
Color-enhancing foods supply carotenoid pigments such as astaxanthin and canthaxanthin, which fish cannot make themselves and must obtain from their diet.
What color-enhancing foods do
Color-enhancing foods are diets fortified with carotenoid pigments to intensify or maintain the red, orange and yellow coloration of fish. The skin color of ornamental fish is largely influenced by the quality and quantity of pigment in their diet, so these foods aim to keep pigment continuously available so that coloration does not fade.
Why diet matters
Most animals, including fishes, cannot synthesize their own carotenoid pigments and must obtain them through the food they eat. Because fish cannot make these compounds, a diet lacking carotenoids leads to duller coloration over time. Continuous dietary supply is the mechanism by which color-enhancing foods sustain bright hues.
The main pigments
Two pigment groups are commonly fed. The red carotenes astaxanthin and canthaxanthin produce red, pink and orange tones, while the yellow xanthophylls lutein and zeaxanthin produce yellow tones. Astaxanthin is a keto-carotenoid of the xanthophyll subclass and is the most commonly used additive; canthaxanthin is also a keto-carotenoid and acts as a lipid-soluble antioxidant.
- Astaxanthin — red keto-carotenoid, most commonly used additive
- Canthaxanthin — red keto-carotenoid, also an antioxidant
- Lutein and zeaxanthin — yellow xanthophylls
How pigments reach the skin
Pigment cells called chromatophores hold these compounds. Xanthophores carry yellow pigment, erythrophores carry reddish pigment, and iridophores produce iridescent effects. Carotenoids absorbed from food are deposited in these cells, and animals that consume astaxanthin-rich algae reflect the red-orange pigmentation in their tissue.
Natural pigment sources
Carotenoids in feed come from natural and synthetic sources. Reported natural concentrations include the microalga Haematococcus pluvialis at about 40,000 mg/kg astaxanthin, Phaffia yeast at 10,000 mg/kg, marigold petals at 6,000-10,000 mg/kg xanthophyll, spirulina at 1,250-2,700 mg/kg, shrimp at 1,060-1,095 mg/kg, krill at 100-800 mg/kg and chlorella algae at 2,000-4,000 mg/kg.
Feed concentrations
Dietary carotenoid concentrations have varied from 60 mg/kg to 700 mg/kg of dry feed. Synthetic astaxanthin is widely used, although studies cited by sources report that natural astaxanthin can have a superior effect on color, increasing redness and yellowness compared with the synthetic form.
Which fish benefit
Fish and invertebrates with naturally red, orange or yellow coloration are the main beneficiaries, since their visible pigments depend on dietary carotenoids. Canthaxanthin occurs naturally in fish such as carp, golden grey mullet and seabream, and carotenoids are also fed to enhance redness in crustaceans such as cherry shrimp.