How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Anna Your Own Question
Anna, Pet Expert/Biologist
Category: Pet
Satisfied Customers: 11513
Experience:  40 yrs.: herps, pocket pets, rabbits, poultry, dogs, horses. Biology degree. Vet assistant.
Type Your Pet Question Here...
Anna is online now
A new question is answered every 9 seconds

I have 3 goldfish (2 comets and 1 common) in a 125 gallon tank.

This answer was rated:

I have 3 goldfish (2 comets and 1 common) in a 125 gallon tank. There are 2 males and 1 female (I think: 2 males are big and had breeding tubercules a few weeks ago and 1 female is much smaller and no tubercules). They were all bought about 1 1/2 to 2 years ago and put in tank within 3 months of each other. Up until the last few days they have gotten along great. For the last few days, the female (smaller one) has been nipping at and maybe tearing the caudal fins of the other 2 (males) and just generally chasing them. The males don't seem to be avoiding her unless she actually nips them and then they flinch away from her. They have always been very playful, chasing each other and resting together until the past few days. The only change is that I moved them from an older 125 tank to a new 125 tank. The new tank has about 8 clumps of hornwort planted in the back. I had the hornwort resting on the bottom of the old tank for about 3 weeks before moving the fish and they seemed fine. All the other decorations (some slate and stone sculptures) are the same. There are also 2 large apple snails in with them that were there for the past 3-4 weeks. Any advice? I love my "common" goldfish!!
Thank you!

I'm especially fond of common goldfish, too, and love to watch them. Some additional information will be useful.

How do you know the smaller one is a female? Has she laid eggs?

Is the smaller one actually damaging the others?

Have you ever seen them chase her?

Thank you.

Customer: replied 5 years ago.
I am not entirely sure of gender. I am going by books I have read. They were all purchased within 2-3 months of each other at the same size and 2 of them are much bigger than 1 of them. The 2 big ones have had breeding tubercules on their gills which I thought only males got. The smaller one who is the bully has not shown any breeding tubercules. But none of them have laid eggs that I have seen. Although according to what I have read they are just sexually mature now.

I am not sure if the fins are damaged or not. The 2 bigger ones (males?) have split fins on their upper caudals while the smaller one's caudal fins are not split.

Yes, they all chase each other, but I have never seen them nip her. She doesn't always nip them but does at least a few times daily. I thought it was a mating ritual at first, but then thought that the male should be doing the chasing/nipping. Plus I didn't think goldfish were so harsh in mating rituals like cichlids are.

Thanks! Lisa

Thank you for getting back to me, Lisa. Chasing and nipping are part of the mating ritual, but they don't usually do any damage. You're right that it's the males who chase, and only males develop breeding tubercles. However, it's very possible that you have three males. The smaller one may simply not have reached breeding condition yet. When no females are present, males will chase each other. Chasing can also be a playful behavior. When it develops into actual aggression, it is because the fish are overcrowded. In a tank as big as yours, that should certainly not be a problem.

At this point, I would just keep an eye on the situation. You don't know for sure that the smaller fish damaged the fins, and there could be other ways this could have happened. If you see any aggressive biting occurring, you may have to separate this fish. Otherwise, I wouldn't do anything at this point. Goldfish do like a little company, so separation shouldn't be done unless it's necessary.

I would test the water. In a newly set-up tank, the nitrogen cycle has to be established. Excessive ammonia or nitrites in the water can cause fin damage. If you see any red streaks on the fins or body, that is another sign of this problem. Here's a website where you can read more about cycling and how to handle it:

You may want to put in some aquarium salt (1 tablespoon per 5 gallons of water) to help with healing. Alternatively, you could use StressCoat. They can even be used safely together, if you want.

So, test your water, monitor the behavior, and add aquarium salt and/or StressCoat to the tank.

If you have more questions, let me know by clicking on REPLY. I hope all will be well.


(If you find my answer helpful, please click on the green ACCEPT button. Thank you.)
Anna and 3 other Pet Specialists are ready to help you