Female guppies fighting!?

[MyDaughtersTank]

Hi all!

Short version (tl;dr): Newly added female guppy immediately started harassing established female guppy, which quickly devolved into an ongoing fight with no one backing down.  What is the best course of action?

 

Full story:

Our display tank is a 20g high, stocked with 1 female guppy (we'll call her the "old female"), 1 female platy, and 5 zebra danios.  Everyone is very peaceful and gets along well.  Tank has been running for three months, is fully cycled, and has lots of hiding spots and line of sight breaks (no live plants, but "lush" with fake plants).  We've had another male and female pair of guppies in a quarantine tank for 4 weeks with no signs of illness and never any hostility towards each other.  The female even dropped fry in the quarantine tank and the adults ignored them despite no hiding spots! 

So I finally moved the new guppies over to the display tank today, and after cleaning up for a few minutes, I came back to observe.  The male guppy was exclusively and AGGRESSIVELY harassing the old female, who is close to twice the size of either of the two new guppies.  The old female was mostly tolerating it, but trying to focus on her algae grazing.  However, the new female was right there with them and she also started harassing the old female- lasered in on her and pecking at her sides.  This continued for a little bit until the old female started fighting back, and then they went at each other for several minutes until I used my net to separate them.  Unfortunately this was not a serious solution and the old female found the new female again and immediately went after her.  At this point, I removed the new female and put her back into the QT.  I also turned the lights off in the main tank for the rest of the day to reduce stress and skipped the evening feed.  As far as I can tell everything has been fine since then.

I tried to research female guppies fighting, but couldn't find much info out there- doesn't seem all that common.  My best guess is that the male saw a large female for the first time and released a hormone explosion into the water, which made the ladies go bonkers??  My plan right now is to reintroduce the new female in a breeder box in the next day or two and let everyone get accustomed to each other's presence before the fully releasing her.  Good plan? Is this normal behavior?  Any other thoughts/suggestions?

Thanks so much in advance to anyone who takes the time to respond.  This is our/my first tank since I was a kid and I am super into it!  I'll be happy to provide more info if needed.

[Ken Dyer]

I have never seen this behavior in female guppies (have definitely seen the males harass the females, that seems like their normal mode). I think the breeder box idea is a good one and likely what I would do in your situation. Usually enough plant cover gives everyone a chance to get away from an aggressor but sounds like you have found Bonnie of the guppy world (of Bonny & Clyde).

Best of luck to you and your guppies and hope Bonnie learns to relax a bit while in time out 😉 

[MyDaughtersTank]

Thanks Ken!  And yeah- the male harassment was definitely normal breeding behavior, just much more aggressive than I had ever seen him with his quarantine girlfriend.  The girl-on-girl fighting on the other hand...

[Fonske]

When I got my first guppies, seven severely pregnant females, each one was packed in its own small bag. I put them all into one tank and they immediately started fighting each other. Non-stop pecking everyone on everyone. I had no other place for them so I just let them sort their differences out. The next day some died (bad ammonia burn in shipping, likely made worse by the fighting too), the remaining ones calmed down. They are still living together with no issues.

I guess I would try your approach with the breeder box. Good luck.

[Alec2cool]

When my juvenile female swordtails grew to be plump, large adults, they began aggressive behavior with one another and it still goes on today. There is no fin rips, missing scales or stressed behavior but they'll nip and chase eachother around for most of the day. A similar behavior happens with my platies but it's far less intense.

Maybe it's some sort of livebearer behavior? Though I will say, your situation seems much more intense than mine. My swordtails can be peaceful with one another but it seems like your guppies have no intention of taking breaks

[MyDaughtersTank]

Just a quick update for anyone searching for solutions for this in the future:

So a peaceful night in the breeder box accomplished nothing, as they were right back at each other a minute after being released.  I let them go for a few minutes to see if they would figure it out on their own, and just as I was ready to give up and went to get the net, they stopped.  

I guess they just needed to establish a hierarchy.  Since then, the bigger one will occasionally lunge at the smaller one, but she immediately retreats a little and its over- no more fighting or any problems that I can see.

[Ken Dyer]

Awesome! Sometimes fish just need some time to settle in and it sounds like your ladies have decided it is too much work to stay upset with each other for long 🙂

Once there is a spawn or two in the tank there will be too many distractions for them to even remember what each other looks like as they get lost in the crowd 😄 

[teenage fish]

You could add more females to the tank since it is understocked. Then the chances of one fish being targeted are lower because there are more options of targets for the dominant fish to pick from.