During the mid-1990s, the British hobby magazine Practical Fish Keeping ran a campaign to alert fishkeepers to the
facts about dyed fish. In this article, from 1998, Dr Stan MacMahon and Dr Peter Burgess explained the damage done to
fish when they are injected with dye:
Some fishkeepers, and possibly even a few traders, may be puzzled as to why so much fuss has
been made about dyed fish. On the face of it, the practice of dyeing or "painting" the fish seems
fairly innocuous and the artificially dyed specimens are certainly very eye-catching in their
various "day-glo" colours. So why push for a voluntary ban on selling them? Our investigations
have revealed the truth behind the dyed fish saga.
Disco fish
Our first encounter with dyed fish was back in
the late 1980s. Thousands of artificially
coloured glassfish, Parambassis ranga (formerly
Chanda ranga) were imported into the UK.
The glassfish, so named because of its naturally
semi-transparent body, obviously makes it an
ideal subject for "painting".
They were seen with fluorescent shades of
either blue, purple, red, yellow, oran ge or green
produced by dyes.
They were (and still are) imported under the
names “painted glassfish” or “disco fish”
(presumably because their almost fluorescent
colours resemble discotheque lights).
How is the dye applied?
Intrigued as to how the dye was applied we decided to carry out a little research. A few coloured
glassfish were sedated in MS222 anaesthetic and observed under a binocular microscope. It
became apparent that the dye is not on the surface of the fish, but lay under the epidermis.
Furthermore, the dye appeared fluid and could be moved slightly by gently squeezing the
coloured area.
This suggested that it must have been injected into the fish at various sites over the body in
order to form the distinctive colour patterns. Our fears were confirmed a few years later when we
were shown photographs of the colouring process, revealing that each fish is individually injected
using a syringe and needle.
The practice of dye injection is undertaken by
fish farmers in some regions of Asia (but not
Singapore as far as we know). Clearly, the
common name “painted glassfish” is a cruelly
misleading description.
If one considers the relative bore size of the
injection needle with that of a glassfish, it
would be the equivalent of us receiving
several jabs using a needle of pencil-sized
diameter - not a pleasant thought.
As experienced fish scientists, we would
never dream of injecting fish of such small
size. No wonder the injection process is alleged to cause high mortalities.