[delta66]

Methods
There are a number of methods for introducing artificial colour to fish, although specific information on methodology is sometimes scanty.

Dyes
A common method of creating "painted fish" is through injection via syringe. Generally, fish are injected multiple times. Fish may also be dipped in a caustic solution to strip their outer slime coat, then dipped in dye. This method is reported to have a very high mortality rate.
Many varieties of "colour-enhancing" foods for aquarium fishes are available to the consumer. Generally, these foods contain natural dyes such as beta carotene and are not harmful to fish, although as with other dye methods, the effect is temporary. One source reports that harmful dyes are sometimes used by wholesalers, however.

Lasers
Fish can also be tattooed using a low-intensity laser with a dye, a process developed for fisheries by scientists but this technique is now applied to ornamental fish.

Genetic modification
Aquarium fish genetically modified to fluoresce in bright colours under white or ultraviolet light are now available commercially in the United States, under the trade name GloFish. The technology was developed originally to produce a fish capable of detecting environmental pollution. These zebrafish are available in several fluorescent colours, protected by a United States patent.

Hormones
It's not introducing any kind of artificial color, but provoking the apparition of mating period tonalities by administering hormones. This is argued to be used for minimizing the stressful effects of transport in fish aspect. This might also be used for making females of certain fish species look more colorful, despite this can also render them infertile. (σημ : πχ ραμιρεζι)