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I have 6 neon tetras in my freshwater tank, but one of them stays by itself on the side of the tank surrounded by plants. Is it normal for it to act this way?

Does it have any large, pale whitish patches on its body? if it does, it could (perhaps) have Neon Tetra Disease, which is first-class trouble. (Contact us for further information on how to cope with NTD.) Otherwise, I wouldn't worry -- just keep an eye on it for a while.

As far as I can tell, it doesn't have any pale white patches. But, I will keep an eye on it. Thanks for the info.

I've noticed that often in a school of fish like that, one or sometimes two of them usually seem to be missing from the group. I had several schools of fish & it was the rare occasion when all of them from one school were schooling together at the same time.

I definitely noticed it with the neons, as I was always counting.

Unless u see something physical its ok, Mine did that too.

10gallon: 8neons 5gallon: 1betta
1oto
2platys

If there are no signs of illness, what else do you have in the tank? If there are no fish in the tank that the neons perceive as a threat then there is no need for them to school.

Neon Tetras and Cardinal Tetras are closely related, and indeed have very simular behaviour patterns (extending right the way to their need to breed in soft, acid water in darkened conditions because both species have photosensitive eggs). I have Cardinals, and I've seen some interesting behaviour amongst my Cardinals that might have a parallel with your 'lone' Neon.

In my aquarium, I have furnishings that provide caves for the Panda Corys to hang out in. One of these furnishings I call the "bogwood boot", because, lo and behold, it's shaped like an old boot with lots of holes in it. It's also covered in a nice thick coating of Java Moss.

Now, one of my Cardinals periodically takes up 'cave dwelling' within this. It's strange to watch at first until some knowledge about their wild behaviour is applied to the spectacle. The specimen in question is, I presume from its slender profile compared to some of the others, a male. Furthermore, when a plump Cardinal (presumably a female) swims past the cave entrance, the 'cave dwelling' Cardinal seems to be 'calling' to the passer by to join it in the cave.

Now, in the wild, Cardinals spawn in dark locations - the uppermost reaches of blackwater rivers (Rio Negro et al) that are completely enclosed by forest canopy and darkened as a result. Over the millennia that the common evolutionary ancestor of the Neon and Cardinal Tetras spawned in this fashion, prior to splitting into separate species, it acquired a mutant gene somewhere along the line that means its eggs can no longer stand exposure to bright light (the gene is present in both species, and also in Paracheirodon simulans, the False Neon, which also split from the common ancestor a good couple of million years ago). So, the fishes now HAVE to spawn in darkness.

Now, next time you look at your 'lone' Neon, try and ascertain if the specimen looks as if it could be a male. If it has a 'male' aspect to it (slender body but otherwise healthy), and is choosing a dark, well shaded location for its spells of apparent isolation from the shoal, then you could be observing the same phenomenon I've been observing with my "cave dwelling" Cardinal. It's a male looking for a female to spawn with. If the fish in question appears to be trying to entice plump members of the shoal to join it when they approach, and chases away slender members of the shoal, then that's what you're witnessing - the fish is a male and it's seeking a spawning opportunity.

So if your fish is healthy, shows no sign of disease, but is hanging out in dark corners on its own, this is what you could be seeing. If the chosen locale in your aquarium is well shaded, if it's one of the darkest spots in the aquarium even with the lights on, then bingo, this is probably what you're seeing.

In fact, I suspect that if you provided your aquarium with some kind of cave facility that the Neons could swim into, your 'lone' Neon would start taking up residence. Give it a try experimentally and see what happens - and if your Neon starts taking up "cave dwelling" as my Cardinal did, then there's your explanation.


Panda Catfish fan and keeper/breeder since Christmas 2002