Achieving Natural Coloration in Fish under Culture

Fish that are colored in nature often acquire faded coloration under intensive culture conditions. Experiments adding top-coated algae to the diets of ornamental fish have resulted in color enhancement. Freshwater red velvet swordtails Xiphophorus helleri, rainbowfish Pseudomugil furcatus, and topaz cichlids Cichlasoma myrnae became significantly more intensely colored when fed a diet containing 1.5-2.0% of a carotenoid-rich strain of Spirulina platensis and 1.0% of a specially grown Haematococcus pluvialis for 3 wk. Though color enhancement was apparent after only a wk, when the fish consumed these doses of algae, lower doses (0.5% and 0.4%, respectively) were not significantly different for kissing gouramis Helostoma temmincki, 24 K mollies Pachouli latipinna, and rosy barbs Barbus chunkiness, were examined after the 3-wk feeding period. Both treatments were significantly more effective than control treatments with no added carotenoid, and better than treatments with traditional carotenoid sources. Color enhancement appeared to occur via natural carotenoid receptors. Thus, color intensity diminished when fish were stressed, coloration appeared only in males in species where only the males are normally colored, and between rosy barbs and topaz cichlids color enhancement was environment-sensitive. Topaz cichlid color developed only after the aquaria were divided into territories and rosy barb color intensified when floating substrate was present. It is concluded that ornamental fishes are good models for color enhancement through diet and that this enhancement may be achieved using products made by marine biotechnology companies.