Dyed Fish 

Several types of fish have been sold which have been dyed by injection with fluorescent dyes of varying colour.  The fish chosen are ones without much colour like the Indian Glass Fish, Parambassis ranga, or albino fish of species like the Bronze Catfish , Corydoras aeneus, or Black Widow Tetras, Gymnocorymbus ternetzi

The most common way this dyeing is done is to inject the fish with the dye at several points. The needle used is not even a very small one.  As you can expect many fish will not survive long enough even to be sold, while the ones that do get sold are much more susceptible to diseases including the viral disease Lymphocystis.  Evidence has also been found of toxic effects of the dye on the fish’s kidneys.

Another way that has been reported as being used is to treat the fish with a caustic solution to remove the slime coating and then put the fish into a dye solution.

There has been a largely successful campaign in Australia and the United Kingdom to stop the sale of these fish.  Selling these fish is not in itself illegal in either country, but arguably the sale of these fish is illegal under common law which requires goods to be suitable for the purpose for which they are sold.  Since these fish have been subjected to a process that will greatly reduce their average life span, it could be argued that selling them as an aquarium fish is an offense under common law.  In addition, if these fish are sold as being natural, this would be misrepresentation.


Tattooed Fish

Tattooed fish are slightly different.  The process was apparently developed for serious scientific research but it is now used by some fish dealers.  The tattooing is done with a low powered laser and is, perhaps, less harmful to the fish than injecting them with a dye.  One fish that is sometimes tattooed is the Parrot Cichlid.  The Tattoos are very big compared with the size of the fish, and must cause disruption to the skin.

Personally I also do not like the idea of tattooing fish, especially if it is just for commercial gain.


Colour Enhancing Foods

Many, but not all, of the natural colours of fish come from the foods they eat.  The plant foods eaten by fish contain Carotenes.  Carotenes are powerful antioxidants that promote health in fish as well as humans.  Colour enhancing foods simply contain plenty of this substance.  β-Carotene (Beta Carotene) is pro-vitamin A.  Fish, humans and many animals can convert this to vitamin A as they need it.

Unfortunately, some people confuse colour enhancing foods with the abhorrent practice of artificially colouring fish.  


Glofish are another type of fish sometimes confused with artificially coloured fish.  Glofish are genetically modified fish containing a gene taken from other species. The name glofish is a registered trademark.