Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Heater burn on fish

Heater burn on a fish
Ancistrus with a heater burn Photo by Craig


Heater burns are generally quite rare but they do occur from time to time. Sometimes a fish will get trapped between the aquarium wall and the heater, or a fairly sedentary fish will choose the heater to rest on. In all cases a heater guard will prevent accidents or better still use an inline or heater/filer.

Initial burn

Initially the burn may not look to bad. The fish will be sulking a little and the scales in the area of the burn will look opaque and possibly a little white. This is a little deceiving because if the burn has gone quite deep in to the tissue things will look much worse in a day or two.

The full extent

After a few days the full extent of the damage will be apparent because the damaged tissue will eventually slough away and leave a deep wound behind. This is the most dangerous time for the fish due to the risk of secondary infections and the loss of vital salts through osmosis.

Deep wounds like this require very careful management especially in the early days if the fish is going to pull through. At the same time it is important not to stress the fish further.


Try to assess the damage, if the burn is very large then sadly the fish probably won't make it and it may be better for the fish if the suffering was ended rather than trying to save it only to leave it suffering greatly for several days before it dies naturally.

If the wound looks to be of a treatable size and this is of course a judgement call which only you can make, then the first thing is to add some salt to the water at the rate of 3gms/l a separate tank would be ideal for this but if one isn't available it will have to be added to the main tank.

The salt will do two things, it will act to prevent secondary infections and it will help ease the osmotic pressure on the fish. It is also worth adding a broad spectrum anti bacteria/fungicide to help keep secondary infections at bay. Then it may be necessary to catch the fish in a soft net and treat the wound topically with Povidone iodine which is a powerful medication at preventing secondary infections, even a very deep wound will probably only require one treatment.

Finally add so wound seal or if this isn't available at short notice add a product like Stress Coat, which will put an artificial layer of mucus over the wound and again it will aid in keeping secondary infections at bay and help with the loss of salts through osmosis.

Fish will often surprise us by simply carrying on as nothing is wrong, this doesn't mean that the fish is happy. Far from it, fish will always try to appear fit and well, to behave oddly would attract the attentions of the ever present predators and the fish would almost certainly be attacked and killed. So it is a very strong instinct in fish to keep looking normal.

Most fish in this condition will continue to feed after the initial shock has worn off but try not to leave any fragments of uneaten food lying around, the aquarium must be kept spotless during the first 10 days or so to allow healing to begin unimpeded by an infection.

Once healing is under way the fish will be much safer but it will still need carefully watching until the wound has completely healed. The fish can then be expected to live a normal life, The scales will grow back but may end up being uneven.