Scale Loss

By: Chewy EditorialPublished:

Scale Loss


I have enclosed a detailed description of my tank setup and conditions, as well as photos of my fancy fantail goldfish. They all appear to be happy and healthy, their behavior is normal, as are their appetites. My two orange fish have lost some scales, the two calicos have not. All four fish have grown since I upgraded to a larger tank last September. Do goldfish molt? Could their recent, rapid growth cause scale loss?

I looked through my disease reference charts and found no mention of scale loss. There are no visible scratches, sores, spots or other signs of injury, and the fish do not fight. I noticed the condition about a month ago. The pH was down to 6.6. I added 1 teaspoon of StressCoat to the water, plus a dose of pH Plus. I did a 30-percent water change and added more StressCoat and more pH Plus. I also lowered the water temperature from 76 to 74 degrees Fahrenheit.

A week later I did a 50-percent water change, thoroughly vacuumed the gravel and changed the filter. Also, (after seeing a copy of the November 1994 AFI article about using salt to relieve stress) I added Doc Wellfish’s Aquarium Salt (4 teaspoons for 20 gallons). I noticed no change after either treatment. The scale loss is no better, nor any worse. Since then I’ve done two partial water changes using bottled water because my water softener is not working (170 to 210 parts per million. I’ve added nothing but salt to the water. Any suggestions?

Today I noticed that one of the orange fish has a torn tail fin. It looks like it might have been torn on something, but I do not know what.


I think we can solve the mystery here pretty quickly. The writer included a full-page outline of his goldfish aquarium setup with his letter, which helped a lot in analyzing the problem. He provided information on the fish aquarium dimensions, water capacity, filtering system, aeration, fish tank decorations (very important for considering physical incompatibilities), fish, water conditions, water change schedule and procedure, and feeding schedule.

Scale loss is not normal for goldfish. They do not molt. Most often scale loss is the result of physical injury — banging against hard objects in the tank (especially during breeding season) or rough handling. It may also result from skin infections, but in this latter instance clear signs of skin deterioration, bleeding and so on are obvious.

Given the time of year (winter), size (age) and type of goldfish, and the tank conditions, it is very unlikely that violent breeding activity caused the scale loss. These fish are not particularly violent breeders anyway. They cannot generate the speeds that regular goldfish can, so scale loss from breeding is less likely.

The most telling piece of information was listed under “Fish.” The writer has a 3-inch (excluding tail) pleco of unknown species in the tank. Plecos suck on the slime coat of goldfish and do remove scales. The photographs the writer provided show patterns consistent with this. The split tail could be a consequence of pleco “attacks” or might be a sign of stress.

In either case the pleco has to go. These physical injuries provide a dangerous opening in the fish’s outer protection against bacterial and fungal infection. Dallas’ first-rate water quality management — especially using salt — probably prevented serious disease from taking hold. Moreover, the salt helped the fish maintain its internal chemical balance despite its wounds.

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By: Chewy EditorialPublished: