Can't tell if Mollies are the problem or my tetras


New Member
Hi all!

I currently have a 45g/36l tank that is fairly heavily planted. I'm still somewhat cycling it (1 month in, but not "well established") and I have 4 mollies. I got 6 serpae's as well after reading online they're peaceful enough if kept 5+. Also have 2 corydoras.

My problem: my black lyretail molly has had the **** nipped out of her fins. The long part has been bitten off all the way down to the fan!
They're all female mollies (yes, I know, that is kind of uncommon (I didn't request sexes)) but they're still being super aggressive towards each other. The black one in particular chases all of the smaller dalmatian mollies around (ESPECIALLY during feeding time) and nips at them constantly.
I thought at first my serpaes were the ones responsible for the black one's tail being chomped but I watched my tank for about an hour earlier and the two small schools actually schooled together completely peacefully. The tetras rough each other up but were super friendly with the mollies.
After about 30 min, the mollies went back to their usual antics of being bullies to each other. I then saw the three dalmatians corner the black one and rough her up. Serves her right, I guess.

My question is: did I just get a crappy batch of all female mollies? Are black lyretails known to be jerks even if they're all females? Would getting 1-2 more help?
I do feel like I've effectively rules out the Serpae tetras as the problem. They've been nipping each others fins a little but that's to be expected.

Thanks in advance for any help!


Well Known
Getting more would help to disperse the aggression. If there’s less of them, the bullied fish are going to be bullied more often, whereas with more fish it’s a bit spread out. However if you see one fish being singled out that may indicate a problem. Sometimes it can be the fish are stressed, or that the fish they’re targeting is weak/sick. Are you sure they are all female? Mollies are easy to sex so I trust you that they’re all female, but males tend to be the ones who harass the females, maybe you have a male hiding in the batch. Still, it’s not unusual for females to do this, but to the extent where her fin is completely gone is a bit much.

I’d recommend getting more mollies, definitely not male though. If there’s feeding aggression you can try dispersing the food in the tank. Having a heavily planted tank as you mentioned you did is good, that will give the bullied fish places to get away and will break the line of sight. If you notice it’s just one fish being a bully or just one fish being picked on, it can help to separate the bully and then rearrange the tank. It’s also good to add enrichment so they’re not always focused on each other, maybe live foods or an air stone, or just changing something in the tank every now and then can help too.

Mind if I ask what your parameters are? Sometimes poor water quality can aggravate fish


Active Member
Dalmation mollies, while pretty are very naughty. I evicted them out of the shrimp tank once I realized they were killing, but not eating them. They also can get semi-aggressive when the ration between sexes isn't optimal for them. Normally, u want to have one male per 2-3 females, bc the females get bothered by the males. It's kinda weird your females are acting ratchet when the ratio seems to be fine.
I had to look up what a serpae was. First thing the search pulled up is that they're "fin nippers".
Honestly, sometimes you have to just keep moving fish from tank to tank (if you have more than one) until they're all cool. It isn't always a hard science.

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