Lost member if newly established betta sorority ... Disease or fight?

[Shiina107]

I recently re established my sorority a few days ago due to a rotten plant bulb from Petco causing a massive ammonia spike that killed my last one... after removing the bulb and seeing the Ammonia was down to 0ppm, i added a sponge filter for extra bio filtration and added a *single* female. She thrived and after 2 weeks I added 6 more. The female that was there showed hardly any aggression to the others and 4 of the 6 I got seemed pretty chill. However, I had 2 larger females, much much larger than the rest. They were about the same size and were at each others throats, but stopped fighting after the 3rd day. I concluded the pecking order had been established... however, one of those 2 was found dead just a few minutes ago, she was almost wedged into a piece of rock, her find all torn and ragged... the other female now lays semi-lethargically in an arch under some rock work. I say semi because she reacts to fish that swim by, and goes up for air every few minutes or swims around a bit just to return to that spot. My ammonia and nitrites measured 0ppm and nitrates <20ppm. I’m freaking out because I don’t want it to be some horrific betta disease. My best guess is since the size difference between those 2 compared to the rest of the girls was so big they found eachother as the biggest threats, and they finally had an all out fight and the larger females fought so hard one died and the other is wounded however the other does not have any fin or body damage that I can make out... my parameters are perfectly fine as you can see and the other bettas are doing perfect, so does anyone agree with my hypothesis or perhaps know what else could have happened? thank you so much for those that respond.

 

[SaraB]

Sounds like bullying to me. How big is your tank? How decorated is it?

 

[Shiina107]

Sounds like bullying to me. How big is your tank? How decorated is it?

20 Long, planted pretty densely too. However there are places that could still use some plants so I will get on that ASAP. My 5 smaller females are all doing fantastic, everyone ate this morning and the aggression between them seems to be almost nonexistent! However, the larger female (possibly) responsible for the others death is still being very shy and secluded, she didn’t even come up to eat.. however she doesn’t act like she’s sick at all, she’ll occasionally chase another around or swim up to the top to breath, then maybe scope around the tank before returning to her little spot. Maybe she’s being territorial? I’m just hoping she comes around soon...

 

[Shiina107]

The original female I had in the tank to “test” acted in a similar way when I added the other girls. She seemed shy and hid herself behind things, almost acting the EXACT same way. After a few days she completely
Opened up and she’s back to being the center of attention.. My best guess was just like original, this new female is stressed. If a fight really did break out, she probably has some injuries I don’t know about, or is just under an extreme amount of stress and she’s currently in full on hiding mode. She has no signs of illness, no signs of swim bladder disease or parasites. So that is my best guess...

 

[Laser]

I don't know if this helps, but I had a male beta in a densely planted tank with 6 rasboras. He was a young beta, but he never moved at all and just laid on the sand. I thought something was wrong with him, but I put him in his own 10g and he started swimming around a lot. He lived for at least 3 years after that.

I think betas have such remarkably different personalities, it's hard to say how they will react to situations.