In recent years, some artificially coloured ornamental fish species such as glassfish (Parambassis ranga, formerly Chanda ranga) and Corydoras catfishes (Corydoras spp.) have made their way into fish stores. Most of them are believed to be injected with various coloured dyes to ‘improve’ their commercial value. Many claim that others are fed on dye-rich foods, however, although this is possible there is little evidence to support this. In contrast, recent evidence regarding the production methods for coloured Parrot cichlids, which were once believed to be colour-fed, has since shown that the fish are injected.

Not only should this practice be condemned on ethical ground, it has also been shown that 40% of glassfish that have been injected with such dyes show infection with Lymphocystis virus causing wart-like lesions of the skin of the fish (Burgess and MacMahon, 1998). By comparison, less than 10% of natural, unpainted glassfish studied had Lymphocystis.

Cosmetic manipulation, which confer no benefit to the fish, should be condemned on welfare ground. It devalues living creatures and treats them as if they were some inanimate object that can be decorated purely for whim or commercial gain!

References
Burgess, P., MacMahon, S., 1998. Why it’s cruel to dye. Practical Fishkeeping Magazine. March 1998.