Suddenly aggressive neon

Starting about a week ago, one of my neon tetras has been fin nipping and chasing the other neons and corydoras. The only changes made around that time were the addition of some wisteria plants and a juvenile female guppy. She has no issues with the guppy. Might wanna add that 1 Neon randomly died about a month ago, the day after a water change.

She's bothering my corys to the point that one seems depressed. Two have had small chunks taken from their dorsal fin. Two other neons appear to have fin rot setting in from their nipped fins. It's all her, and I'm honestly tempted to just get rid of her.

Tank is a 29 gallon. Only inhabitants are 6 Neons, 6 Harlequin Rasboras, 6 Corycats and 1 guppy. Numbers are all coming up good, water changes once and sometimes twice a week. All fish aside from the guppy have been there since late February.

She looks perfectly healthy. Acts like she's starving. Seems like she's discovered that nipping the corys = food bits flying around when they take off. But what's up with her mood change?

 

Is the tank cycled? I do find her behaviour quite odd, and I’d liken it to her not feeling safe in her surroundings. Is there any cover in the tank where any of your fish can retreat to?

Pictures will help

 

I'll get some pictures tomorrow when I turn the lights back on. I do think I need more plants, but waiting to add more because the current ones are growing fast. Fishless cycle completed around mid-February. No ammonia or nitrites, nitrates around 10, ph runs 6.8 to 7.2.

The Neons mostly hang out around the Amazon Swords or in a cave. Corys do occasionally run them out of said cave. There's a ship ornament and also barrels that the Neons never touch.

 

The more plants the better

 

Tetras can get nippy and aggressive, but usually just among their own kind and it rarely does more than stress. Usually the nipped fins heal easily. They usually pick spots to hang out in a loose shoal and unless disturbed by human interference. But as soon as one of them enters the little territory of another they chase and nip each other.
It sometimes helps to change the structures in the tank. A big plant or a piece of driftwood breaking lines of sight and/or creating spots with less current seem to be working.

What I find unusual here is, that it gets nippy towards other fish. Sure it's not just picking food from the cories? And that the neons are in a cave... how densely is your tank planted and/or decorated? How bright are the lights?

Also fish don't get depressed, that cory is just stressed a lot.

I'd need a pic of the tank to say more. It all sounds like the setup is not holding up to the fishes needs.

 

Acts like she's starving. Seems like she's discovered that nipping the corys = food bits flying around when they take off.

From what you said there, I'm getting two impressions.

You say acts like she's starving... Could it be as simple as she's actually hungry? How much are you feeding them? What are you feeding them? How often? Maybe she's missing something nutrition wise, doesn't sound like she's getting out-competed.

At first I thought you meant chunks of Cory flesh flying around! But I take it you mean food on the substrate? That doesn't sound good, maybe vacuuming the gravel more often (which would make the water cleaner=less ammonia/nitrite=less stress) would help? Even if your tests are reading 0, if you never gravel vacuum it'll create pockets.

Oh and it's weird for Tetras to hide, sounds like there's too much bright light. A good solution is more plants, try looking up a video or pictures of their natural habitat and work towards replicating that.

They also might be stressed because their school is so small, especially if they recently lost a member (schooling/shoaling fish have surprisingly complex social structures so losing a valued member can really upset the group dynamic). Also because you have two other school of different fish the same size, and possibly not enough to break up the open space so they all have their own areas. Maybe get another 1 or 2 neons before you resort to giving her away?

 

You say acts like she's starving... Could it be as simple as she's actually hungry? How much are you feeding them? What are you feeding them? How often? Maybe she's missing something nutrition wise, doesn't sound like she's getting out-competed.

I doubt that it's just hungry. Tetras always act like starving piranha in my experience.

Oh and it's weird for Tetras to hide, sounds like there's too much bright light. A good solution is more plants, try looking up a video or pictures of their natural habitat and work towards replicating that.

Excellent idea!

They also might be stressed because their school is so small, especially if they recently lost a member (schooling/shoaling fish have surprisingly complex social structures so losing a valued member can really upset the group dynamic). Also because you have two other school of different fish the same size, and possibly not enough to break up the open space so they all have their own areas. Maybe get another 1 or 2 neons before you resort to giving her away?

I'd wait with that. With the info that some tetras died lately it sounds like the source-store is contaminated.

 

I doubt that it's just hungry. Tetras always act like starving piranha in my experience.



Excellent idea!



I'd wait with that. With the info that some tetras died lately it sounds like the source-store is contaminated.

Very good points! Take any advice from me with a grain of salt as I'm a beginner as well

 

In my experience male Neon Tetra often claim a small territory including plants and chase away other males and other fish they are not interested in. They then entice female Neon Tetras to spawn there.

Cardinal Tetras do not seem to do this. I believe they are group spawners.

While this aggressive behaviour can be unwelcome I have found it is reduced when the temperature is lower, though this can be hard to maintain in summer.

70 to 74F usually does it. In fact I believe 74F might be the optimum for Neon Tetra in any case.

Neon Tetras only need half a flake each per day to maintain their bodyweight (according to scientific study).

 

She definitely isn't hungry. They get fed once or twice a day. I use multiple foods; bloodworms, brine shrimp, micro pellets, flakes. Not all at once of course. That particular Neon often ignored the food and hovered over the Cories while they ate their shrimp pellets. She'd eat the little pieces that floated away while they ate. If they weren't eating, she'd peck them.

Anyway.... I took the Neons out. All 6 are now in my QT until I'm sure they aren't sick. They're gonna go to a friend who wants to add to his school of Neons. My Cories are much happier with them gone. I'm placing my focus on growing more plants for now.