who could be the mystery nipper?

[Sgooosh]

Hi! In my 75g a lot of fish are getting tiny nips, almost everyone has one except for the single rummynose tetra and wild guppies
This started around a month ago, and before that I haven't added any new fish for the whole summer

I recently added 2 small american flagfish (Which will be moved outdoors next summer) like 2 days ago

Here is my stocking
american flagfish (1 medium male, 1 small female)
many large swordtails (5+)
A few adult platies, around 4 and some juveniles
characodon lateralis (2 big females, 1 male, and some juveniles)
A lot of guppies, fancy and wild type, 10+
female pearl gouramis, 3
cories (one very big and one medium sized)
harlequin rasboras, 9
one single rummynose tetra
Bamboo shrimp, large, 2

I'm wondering what could be causing all of the little nipping? I've had this stocking since summer, and no problems at all until the temperature started to drop.
another thing i noticed is that there's less plant cover now after the heat of summer
Could some fish have entered a breeding season that makes them aggressive?
Fish that are getting nipped are the swordtails, certain fancy guppies, harlequin rasboras, and especially cories(Which i assume is because i only have two left)
In terms of size, pearl gouramis are the largest, characodons and swordtails are about equal, platies are next, then rasboras, and lastly guppies.

 

[Magnum Man]

I’ve wanted to try flags again l, but when I had them before, I found them nippy ( this was before I installed my RO filter for fish water, so the tank had issues ), not sure if that’s why they were nippy

 

[Sgooosh]

I’ve wanted to try flags again l, but when I had them before, I found them nippy ( this was before I installed my RO filter for fish water, so the tank had issues ), not sure if that’s why they were nippy

I'm not sure if flags are the issue because I just added them a few days ago and the nipping has been happening for a longer time, but i think they may have been adding to the existing issue

 

[GaryE]

There are many suspects. Characodon can nip, as can some swordtail males (individuals, not really a species trait, if the tank's small or crowded). Jordanella can be nippy.

That's very odd stocking. Most Characodon keepers give them their own tank, because of their conservation status. I was never able to get them in my hardwater days, but a lot of Goodeids dislike tankmates. It will be interesting to see how they react to the flagfish.

 

[Sgooosh]

There are many suspects. Characodon can nip, as can some swordtail males (individuals, not really a species trait, if the tank's small or crowded). Jordanella can be nippy.

That's very odd stocking. Most Characodon keepers give them their own tank, because of their conservation status. I was never able to get them in my hardwater days, but a lot of Goodeids dislike tankmates. It will be interesting to see how they react to the flagfish.

oh, okay, there is two males now because one of the females turned into a male, maybe that recent transition is making him very aggressive. I've only had one swordtail male for a long time but that one decided it wanted to be king instead! The other swordtail male is old and quite docile. I think this is probably the culprit

The characodons were kind of an uneducated buy, because I assumed that goodeids are good community fish without realizing that it isn't a single genus like guppies or swordtails. I had them in their own 10g but they wouldn't stop growing so I moved them into my big tank. The fish are all pretty much equally sized

As the temeperatures stabilize hopefully this will stop!

 

[GaryE]

Xiphophorus (swords and platys) are as complex species-wise as Goodeids. In the hobby, we tend to have three species, helleri, maculatus and variatus, and even those may well be extensively hybridized. But in nature, there are at least 28 described species.

Males can also take up to a year to show their gender. There are early and late bloomers. With one wild species, X. maeyi, I had to wait 13 months to sex them. Late blooming males live far longer than their quicker maturing brethren.

I never got Characodon, as I said above. But many of my Goodeids were downright aggressive to other fish. I would combine them with other goodeids in my then 55 and 75 gallon tanks, but that was only til I could give them their own species tanks.