Why is my goldfish turning black?


why is my goldfish turning black

One of the main attractions of the goldfish is its vibrant natural colour, so it is not surprising that owners get quickly concerned when they notice that their pet is developing black patches. Owners worry that something is really wrong and this could be the case, but there are various reasons why a goldfish turns black and not all of them are bad.

We bring you the possible reasons why your goldfish is turning black and importantly …. the solutions.

why is my goldfish turning black

Should I be concerned that my goldfish is turning black?

It is actually not that common for a goldfish to start changing from gold to black, but it is much more common for them to lose their colour and change to white or yellow.  Black is actually a difficult colour in goldfish and those that start out as black often in time, change to white or yellow. Sometimes when a goldfish starts to turn black, this can be an indication that all is not well, but not on all occasions as sometimes the colour change is completely natural. The important point is that if your goldfish starts to turn black, you must use a process of elimination to ensure that they have not developed a health problem.

Should I be concerned that my goldfish is turning black?

It could be pure genetics

This may sound strange, but some goldfish are more likely to change colour than others. Whilst turning from the usual vivid orange to black is very unusual, it is not impossible!  Many cheaper goldfish for sale are in fact mixed breed goldfish and in reality may have gone through several colour changes. Often these goldfish can be spotted as they are usually displaying some different colouration patterns. The most usual time for these changes to take place is as the fish matures into an adult goldfish when they are about one year old. Often these changes are really gradual to begin with and your goldfish may well develop white and yellow patches as well as black ones. The colour of your goldfish is also determined by the type of scales he has – especially metallic ones as these are shiny and reflect colour in different ways.

Some pure bred goldfish can also develop some black markings -particularly on their fins, but this is just their individual marking and nothing to worry about as they can still live to a good age.

It could be pure genetics

Your goldfish getting camouflaged

Often fish have markings on their skin that helps them to blend in with their background – which in the wild is essential for their protection. Goldfish do produce the black pigment melanin in their body. Sometimes, if goldfish are in a tank that has a dark wall behind it, they start to produce more melanin that will give them a black tip to their tail or fins and sometimes black scales too. This is your fish’s natural defence system ensuring that he blends in really well with his background as he would do in the wild.

Your fish has become diseased

Although this is quite rare, there is the chance that your goldfish has developed the disease ‘black spot’. This disease impacts goldfish living in a pond rather than a tank and can also be found in wild fish. Black Spot is a parasitic fluke disease that is spread by infected water snails. If your goldfish is living in a garden pond, the fish could also have contracted the disease from bird droppings.  The larvae of the parasite burrows under the skin of the fish and lays its eggs there and the spots burst and release the parasite.

When a goldfish develops Black Spot, usually several black spots appear on their body and in bad cases, many black spots develop all over the fish. If you suspect that your goldfish has Back Spot, watch his behaviour for the telltale sign. Goldfish find the dark spots on their bodies and tail very itchy and will be trying to relieve the itching by rubbing their body against weed or decorations.

Black Spot actually sounds worse than it is, but you must take swift action to break the life cycle of the parasite and this means clearing away all the water snails in your pond. Be very careful as you do this to ensure that you remove all the snails as there could well be some tiny baby snails hidden in weed.

Your fish has become diseased

Could your goldfish be stressed?

Goldfish can be stressed by a sudden change in their environment and also by the introduction of other goldfish or animals into their tank or pond. If you have recently bought the fish, the stress can be traced back to the way they were shipped or transported to the pet shop. It may well take some time for your fish to settle and it is important to monitor their behaviour – especially with the other fish – but usually time is a healer for stressed goldfish.

Is there ammonia in the fish tank?

This is the most common reason why goldfish start to change colour. If ammonia is the cause, black spots usually begin to appear on the fins. Slowly the change in colour affects the whole body and on close examination, the scales look burnt. Ammonia is a toxic chemical that is produced by the fish in the tank and also from decaying plants and fish food.

If you suspect ammonia in the water, change at least 50% of the water immediately. Ideally, you should have an ammonia testing kit as you need to regularly check ammonia levels as they should be 0 PPM as two parts per million of ammonia can prove fatal to goldfish.

The tank needs to have an effective filtration system and 10- 25% of the tank water should be changed every week.

The gravel in the tank will also need to be regularly vacuumed and the glass on the inside of the tank cleaned as these all help prevent a build-up of ammonia. 

It is important to remember that goldfish are messy and if the tank is not cleaned regularly and thoroughly, that a high level of ammonia will soon develop and it could poison your fish.  It could be necessary to revise your maintenance schedule for your tank.

The good news is that when you first spot the appearance of the black spots on your fish, their skin is starting to heal. Always watch out for any unusual swimming patterns or laboured breathing in your fish as these too are signs of ammonia poisoning. Be sure that you are not over-feeding your fish as food waste quickly rots in the tank, producing ammonia.

Is there ammonia in the fish tank?

What if I don’t know what the problem is?

If you cannot find out what is causing the changes in your goldfish, there are several more unusual diseases that could be the problem so it is best to seek the advice of your Vet.

What if I don’t know what the problem is?

Can goldfish turn gold again?

Depending on the cause of the change in colour, your fish may regain its shimmering orange colour. If the black marks  are signs of ammonia poisoning,  the main concern is that the ammonia will not have been fatal. If you take prompt action and monitor your goldfish really carefully he could well recover. In this case, the black spots will slowly heal as they are burns on your fish. This will be a lesson learned and to avoid a repeat of the problem, it is best to regularly test the ammonia level of the tank water. It is also also worth considering whether the problem occurred because you have too many fish – for example, five fish in a 20 gallon tank could mean that the fish do not have enough space and that too much ammonia is accumulating.

Can food help my goldfish stay vibrantly coloured?

Many quality goldfish foods contain carotenoids and are advertised as ‘colour-enhancing’ food.  Certainly they can help improve/maintain the colour of your goldfish. As your fish’s vegetable treats it is well worth feeding him garden peas and carrots as these vegetables are both rich in carotenoids. 

If the colour change has been caused by genetics, another colour change is less likely to occur. Although this could be disappointing to learn, the important fact is that your goldfish is very healthy.  Armed with the knowledge of the various answers to the question ‘why is my goldfish turning black’, will give you the confidence to establish what has caused the change and how to deal with it promptly.   

Frequently Asked Questions

Will the black on my goldfish go away?

It depends on what has caused the black on your fish. If the black patches have been caused by ammonia burns, these will in time completely heal. If your goldfish has changed colour because he is trying to camouflage with his surroundings or because of chromosomes, it is unlikely! Having said that, your goldfish is happy and healthy and his new colourings make him unique.  

How do you treat an ammonia burn on a goldfish?

Prompt action is required if you suspect ammonia burns. You will need to change at least 50% of the tank straight away and replace the water with treated water. It is good to vacuum the gravel to get rid of decaying food and to clean the inside of the tank glass too. Invest in an ammonia testing kit to keep an eye on the ammonia levels in the water. 

Do goldfish turn black when sad?

One of the many reasons that a goldfish can develop black spots or patches is stress. Goldfish can be upset by a sudden change in their environment and by the addition of other goldfish or animals to their tank. It will take time for you goldfish to recover and not feel so sad and stressed, but they will recover.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Content Disclaimer

Whilst every effort has been made to ensure the information on this site is correct, all facts should be independently verified.

Amazon Associates Disclaimer

As an Amazon Associate I earn from qualifying purchases.

Useful Links



Facebook | Twitter | E-mail

%d bloggers like this: