Boesemani Rainbow missing scales - Injured or sick?

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Aquarium Advice Regular
Dec 15, 2009
I have an adult male bosemani rainbow that has missing scales around one of its gills, almost like they've been scraped off. You can see it clearly in the picture below. Can anyone tell me if this is an injury or a disease?

Here is some more info:

It has been this way for a few weeks. I keep hoping it will get better but it hasn't improved - if anything it has gotten worse.

It is barely able to move its fin on that side. It spends some time sitting in the left upper corner of the tank but also swims around seemingly normally most of the time.

It is in a well-established 75 gallon tank and I've had the fish for about 2.5 years. There haven't been any recent changes to the tank. Tankmates include three other rainbows (1 male and 2 female), a roseline shark, congo tetras, and some smaller tetras. Filter is Fluval FX6, I do regular water changes, feed flakes + frozen shrimp/bloodworms.

Any help would be appreciated. Thanks so much.


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It looks like a bacterial infection and a possible gill tumour.

How long has it been like this?
Did the fish develop a pink coloured growth from under the gill cover by the pectoral (side) fin?

Gill tumours are sort of common in rainbowfish and might be linked to Fish Tuberculosis (TB). The tumour appears as a small pink growth coming out from under the gill cover. Over time it grows and a pink mass will become quite noticeable around the edge of the gill near the pectoral fin. There's no cure for tumours like this.

The skin dissolving on the side of the body (above and below the pectoral fin) looks more like a bacterial infection. In minor cases you can use salt and it might help. But you might need something stronger like a liquid broad spectrum fish medication that treats bacteria and fungus.

Be careful using medications on rainbowfish because they are sensitive to lots of chemicals.

Rainbowfish need lots of plant matter in their diet and at least 50% of their diet should be plant based. They are more prone to tumours and other diseases if they don't get sufficient plant/ algae matter in their diet.


To work out the volume of water in the tank:
measure length x width x height in cm.
divide by 1000.
= volume in litres.

There are 3.785 litres in a US Gallon
There are 4.5 litres in a UK gallon

When you measure the height, measure from the top of the substrate to the top of the water level.

If you have big rocks or driftwood in the tank, remove these before measuring the height of the water level so you get a more accurate water volume.

You can use a permanent marker to draw a line on the tank at the water level and put down how many litres are in the tank at that level.


Before you add any medications, do the following:
Test the water for ammonia, nitrite, nitrate and pH.

Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.

Do a 75% water change and gravel clean the substrate. The water change and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.

Remove carbon from the filter before treating with chemicals or it will adsorb the medication and stop it working. You do not need to remove the carbon if you use salt.

Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 2 heaped tablespoons per 20 litres and if there is no improvement after 48 hours, then increase it so there is a total of 4 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate (1-2 heaped tablespoons per 20 litres) will not affect fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.
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It appears to be an infection of some form possibly caused by fighting with the other male or a wound that has festered. Because it is a rainbowfish tho, there is another possibility and that is fish TB. Not to be an alarmist but if it is TB, it is transmittable to humans so you really need to be careful when dealing with that fish and the tank water, especially if you have open cuts or wounds on the parts of your body that get wet.

The recommended course would be to isolate the fish in a bare hospital tank and treat with Kanamycin if you have a Ph level over 7.0 or in lower Ph water, Nitrofurazone or Tetracycline are the recommended antibiotics. These are broad spectrum antibiotics so if it not TB, you should start to see some results within 7 days. If there are no results, it is more likely to be TB and while the treatment would be the same, the treatment time is a long process and most choose to euthanize the fish over the expenditure for months of meds. So any way you look at it, the fish should be taken from the main tank and treated separately.

Hope this helps. (y)
Thanks very much Colin and Andy. I unfortunately don't have a second tank to isolate it. I will try the salt and see if that improves anything.
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