A discussion of enhancing colors of ornamental fish would be incomplete without mention of dyeing and painting fish, and feeds containing hormones. The practice of painting essentially colorless fish (e.g. glassfish) has become widespread. The neon colored paint is non-toxic, but the handling and painting, coupled with shipping stress often invites disease problems. These fish often contract ich (Ichthyophthirius multifilis) and fungal infections. The paint is shed in time and the fish returns to being colorless which may be more disturbing to someone paying a premium for "painted" fish. Dyeing colorless fish has recently become popular. The fish are immersed in water containing dye and the immersion and handling may lead to the aforementioned disease problems. Hormones may be used to enhance fish coloration by causing a false early maturity. Testosterone supplied in the diet likely allows a premature storage and expression of pigments in the chromatophores. Fish that often exhibit drab juvenile coloration may then show full adult coloration. Fish treated with hormones often become all male, sterile, and require a continuous dietary supply of hormones to maintain coloration. The sex of juvenile fish is often ambiguous and hormone diets, most often containing testosterone, create all male fish. Uncontrolled doses of testosterone sterilize fish. Endogenous production of hormones ceases, so coloration is not maintained when fish are taken off the hormone treated feed. Fish feeds containing hormones do have legitimate commercial uses in Tilapia (Oreochromis spp.) diets (Teichert-Coddington et al. 2000). Tilapia growers are hampered by the fact that this cichlid often matures prior to reaching market size. The fish farmer often ends up with mixed size classes and stunting of fish in growout ponds if the tilapia are allowed to mature and reproduce. Feed energy also goes into producing gametes instead of fish flesh. Feeds containing hormones have been used to provide all male groups of tilapia for growout. These diets contain testosterone since males grow faster. The feed is administered to juvenile fish prior to growout and is currently undergoing FDA approval for food fish. Given the current status, this feed is probably not widely available to ornamental fish growers and hobbyists and would be of little use enhancing color of fish already sold as adults which encompass most ornamental fish with the notable exception of cichlids. There is no specific way to tell if a fish has been fed a diet containing hormones except to be vigilant of the fish you purchase. If it looks to good to be true, it probably is!
Water quality may also play a support role in determining the color of ornamental fish. Degraded water quality increases stress on captive fish and may dull fish colors. A high quality biological filter and routine -at least bi-weekly- water changes will provide an environment enabling fish displaying their brightest colors.
Hobbyists may wish to experiment with their own color enhancing diet. There are several recipes for gelatin-based feeds available in other publications, notably Moe (1982) and Konings (1993). I would recommend the protein portion of these diets (e.g. shrimp, fish, squid) be replaced with salmon fillets. Salmon are a good source of carotenoid pigments that enhance reds. Additionally, all essential amino acids will be supplied using salmon as a protein source and the higher lipid content in salmon will promote better utilization of the protein. The addition of high quality pure spirulina powder will enhance blue pigments. This can be purchased from aquaculture suppliers. Any gelatin based diet should be stored frozen to maintain freshness and used within several weeks. Feeding a varied diet rich in sources of pigments along with good water quality will ensure captive fish develop vivid colors.
Moe, M.A. 1982. The marine aquarium handbook – beginner to breeder. Green Turtle Publications, Plantation, FL.
Moyle, P.B., and J.J. Cech. 1988. Fishes an introduction to ichthyology. 2nd Edition. Prentice Hall, Englewood Cliffs, NJ.
Fujii, R. 1969. Chromatophores and pigments. pp. 301-353 in W.S. Hoar and D.J. Randall (eds.). Fish Physiology. Volume III. Reproduction and Growth. Bioluminescence, Pigments, and Poisons. Academic Press, New York, NY.
Konings, A.(ed.). 1993. Enjoying Cichlids. Cichlid Press.
Teichert-Coddington, D., B. Manning, and J. Eya. 2000. Concentration of 17alpha-Methyltestosterone in hormone treated feed: Effects of analytical technique, fabrication, and storage temperature. Journal of the World Aquaculture Society 31: 42-50.