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My fish are changing colour

A fairly common situation arises when fish literally change colour, either all over or just parts of the body.  The most common situation is when previously coloured fish turn white.  Fish skin colouring is a complex subject.  Fish skin contains different types of pigment cells or chromatophores, which are under the control of the hormonal and nervous systems.

My fish are changing colour
My fish are changing colour

Fish which are diseased often change colour, but this is usually a fading/darkening/dulling of the skin rather than an actual colour change.  There are a few conditions in which there is a colour change but these are rare. 

The most common causes are either nutritional deficiencies, so one could try a change of diet, water chemistry such as pH or hardness, or simply genetics.

In virtually all cases the fish appear perfectly healthy apart from the colour change and eat and swim normally. So apart from perhaps changing the diet and checking water parameters there is nothing that can be done to reverse the colour change.

As a thought, it might be a little upsetting if your goldfish becomes a whitefish, but pity the koi owner who has paid several hundred pounds (or dollars) because of the fish’s perfect colours / pattern, simply to watch the colour and patterns disappear!!!!

My fish are changing colour

When a fish develops a white bar of color from top to bottom, right through the middle, they are going to die. There are two causes for this, a form of vascular shock sometimes unexplained, sometimes caused by bacterial infection especially localizing in and spreading from the kidney can cause the fish to blanch in the middle. And Pleistophora (Neon Tetra Disease) infections will also cause that. If you can save them with any combination of temperature, food or medication please let me know.

If a fish develops a black band from top to bottom, right through the middle, it is dying from stress. (This will happen in Angelfish, Gourami, and cichlids. I have also seen it in some Platies. Increasing oxygenation, and heat to 80 DF and offering minimal crowding and stress MAY save it. A Maracyn or similar dip may help.

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Dr Erik Johnson

Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.