Two goldfish fighting in a large tank

[not_a_tree]

Hi there!
I have a fighting problem with my two common goldies who share a 90 gallon tank. When they were smaller I used to keep them with a black moore (now that I know more, fancies are in a different tank) and even though they were faster, and had better vision than the moore I never had any fighting or bullying in the tank.
As they grew I moved the common goldfish to a 30 gallon tank where again they lived in peace for quite a while until one day they started fighting (~1.5 years of age, both happened to be males). Originally one of them was more dominating due to a larger size so he would try to get to the food first, but nothing violent. But that day the fight was just out of nowhere, and it was the smaller one who chased and attacked the bigger one (as if he got fed up with being pushed around-not literally). So I figured they had territorial issues as 30 gallon was getting to small for them. I transferred them to a 90 gallon where again everything was fine for for about 1.5 months and then again they grew some more and started fighting again. I separated them with plexiglass (or whatever this material is called) and two months later I still don't understand why they can't get along. Sometimes they are able to mind their own business without bugging each other, even for a whole day but then I have to separate them again as scales go missing, and pushing and chasing ensues.
Is a 90 gallon still too small? Is it because there are only two of them and the aggression becomes concentrated? Is it because they are both males? Does anyone have any ideas?
I'll appreciate any help!

P.S. Water quality is fine, I do regular water changes (biweekly and often every week) and water checks.

[Somervell]

Are you positive that they are both males? That sounds like spawning behavior to me.

This may sound really, really strange, but I have tried it with aggressive goldfish and it has worked. Try re-tankscaping the 90 and introduce the least aggressive fish to the tank before the more aggressive one. I have done this twice, and both times, the re-tankscaping creates a "new" environment and the fish have stopped being territorially aggressive. It's worth a shot, anyway. Good luck with the situation.

[not_a_tree]

Somervell: Both of them have tubercles on gills and fins, just like on the pictures here: http://www.aquariacentral.com/forums...h-(with-photos)!
So I guess they are male. Also, it does not seem like spawning behaviour because I cannot identify a single chaser. Both of them pick on each other equally and not so much for the purpose of chasing but rather pushing and nipping.

Try re-tankscaping the 90 and introduce the least aggressive fish to the tank before the more aggressive one.

This sounds very interesting, thank you! I have tried rearranging decorations (luckily I did not plant the tank) but with goldfish remaining in the tank. I also read somewhere that their hierarchy depends on who is the first one to enter the new aquarium. I don't know how true that is though.
Does it matter if I use the same plants? Or should I put new or lately unused decorations instead?

[Arakkis]

you got two boys duking it out.. here's a tip.. cool the water down. the warm water will cause the boys to go into breeding mode. Plants won't help unless theres so much they cant see eachother

[not_a_tree]

Arakkis: I don't use a heater, and it's winter now where I live. Aquarium water temperature is 18°C.

[Arakkis]

about 65F.. hmm should be cold enough. are they on a high protien diet? If they are switch to a low protien or wheat germ diet, scale back feeding. high protien can cause an increase in testosterone. Also feed them less, they should probably only eat every other day to every 3 days at 65F as thier metabolic rate is thethered to temps. Other than that they shouldn't have tubercules at that temp.. if you got a really nice friend with a chiller, hook it up and slowly drop the temp cooler to lets say 55~60 over the course of a week or two would cause them to "hibernate" and not fight.

[Somervell]

This is a really interesting thread. I am interested in what Arakkis is saying about temps. In the case where I had to rescape, I had two male fancies in a 60. I am surprised that in a 90 you would still have territorial aggression. I had also never heard the information about protein content increasing aggression in goldies. I am going to definitely have to do some research on that one.

In answer to your question, I didn't change the decor except to move it around and add a couple of plants for more hiding area. I did this both times that the rescaping was successful. Not sure why it worked, but I was glad that it did!

[Arakkis]

about the protien intake, its documented that the increased protien will increase the levels of active testosterones, which means that the hypothalmus is releasing more enzymes than usual that in turn and causing the testes to increase production (which can also make the fish develop sexually faster), in turn may kickstart a breeding cycle, which increases agression. Though this normally doesn't happen in cold water since the protien will not metabolize properly due the the decreased effectiveness of internal bacteria which causes gas/bloat as a side effect. Its interesting that they are forming tubercules at 65F which to me is not normal unless this is the warmest it's been in a long while

Also since the bacteria behave at differing levels of efficiency at different temps, changes thier dietary requirements thoughout the year in quantity, type, and frequency. If this werent true we wouldn't have differnt pond feeding formulas.

[not_a_tree]

Arakkis: I also did not know about the link between protein and aggressive behaviour in goldfish, thank you for your comment!

Its interesting that they are forming tubercules at 65F which to me is not normal unless this is the warmest it's been in a long while

In terms of temperature, I would say it's usually between 64.4F and 66.2F (18C-19C) since during the day we turn on the heat up more than at night. I would say that in general water temperature does not exceed 75.2F(24C) and does not fall below 64.4F(18C) over the course of a year.

are they on a high protien diet? If they are switch to a low protien or wheat germ diet, scale back feeding. high protien can cause an increase in testosterone.

I feed my goldfish with Omega One (33% protein content) most of the time. Should I switch to something like Hikari Wheat Germ pellets (30% protein content)? Or maybe you have some other suggestions in terms of brands?

[not_a_tree]

*

my two common goldies

One of them is actually a comet I think though, but I am not sure whether comets are classified as common goldfish or belong to a separate class.