From The Aquarium Wiki
A dyed fish is a fish that has either been dipped in dye, painted on, laser blasted, or injected with dye multiple times (tattooed). In the case of the "painted" glassfish (Parambassis wolffii), the fish is injected with a colored latex. This process, while creating eye-catching fish, stresses out the fish, kills most fish, and creates huge problems for the fish in later life in the form of diseases, skin lesions, and weakened immune systems. It is estimated that about 80 out of 100 fish die after being treated with dye.
Quite often the outer mucus of a fish is stripped off by dipping it into a corrosive liquid, thus starting the process.
Dyed fish can be very lethargic and unhealthy, unlike their normal counterparts. Many suffer from the Lymphocystis virus or kidney failure. They will be more susceptible to bacterial and parasitic problems within the tank due to a lower immune system if they have been injected or dunked to create the artificial colours.
In the United Kingdom, the offical trading body of ornamental fish resellers (the OATA) doesn't ban its members from selling these animals. It does however recommend that its members not sell them. So, sadly, quite a few do sell them.
There is a lot of support for a ban of this treatment from UK aquarists.
The monthly magazine 'Practical Fishkeeping' (PFK) started a Dyed Fish Campaign in 1996 and is raising the profile of this issue as most shop customers are ignorant of this practice.
Currently PFK say it has the support of 75% of pet shops retailers throughout the country to agree not to sell dyed fish. But with ignorant customers and these 'pretty' fish selling for a good profit, it's proving too unpopular with small pet shop retailers wishing to make a quick buck.
Loophole in the Law
In the UK it is illegal to actually dye the fish as it is classed as animal mutilation. But as these fish are brought in from outside the country, this means that the animal can be mutilated in another country and then brought in quite legally.
There are no regulations currently in place that prohibit the importation or marketing of dyed, painted or tattooed fish.
What can we do?
When you visit a pet or aquarium shop, ask a member of its staff if they sell dyed fish. Tell them you don't like the practice and you may take your trade elsewhere if they do, encouraging friends and family to do the same. By buying anything from a store which does stock dyed fish, it will only be encouraging them to carry on business regardless of opinions of single customers. It is better to boycott than buy!
"Polka Dot" Kissing Gourami
Dyed Indian Glass Fish. One of the first dyed fish since the 1980's.
"Cotton Candy" Blood Parrot
Tattooed Blood Parrot