Least killifish bpther ghost catfish

I would suggest the culprit could be either the killifish or the neon tetra, more likely the latter. Disease might be another possibility, but that would probably be more obvious; if the catfish had their feelers and now they are shorter or missing, it is more likely the other fish. The Least Killifish I assume is the species Heterandria formosa? How many neons are there? Keeping too few (less than 6) of any characin (tetra are characins) can cause aggression. And how many Glass (Ghost) Catfish? These are more settled in groups of say 5+.

Byron.

I'm guessing neons too. They're small but kinda nippy as most tetras can be with long fins or slow (non) movers like ghost cats. I haven't kept least killies but other killies I have kept were also not shy about "tasting" tankmates if they could. No one usually suspects quite small fish, lol.

Heterandria formosa are actually not killifish at all. They are livebearers closely related to guppies. I dont know why they got that misleading label. I'd also be surprised if they were the culprits here. Mine are very shy and probably too small to do that kind of damage to a catfish's barbells.

psyche said:

It is definitely the LKs, I have watched them do it 5-6 times now. One will eye the end of the barbel, line up and nip it. This will continue until the catfish moves far enough away that they lose the target. I have 8 cats, about 10 tetras, and maybe a 7-8 LKs although only a couple are adult. Keep in mind ghost cat barbels are very fine and long.

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Given this, I would separate them, meaning not have the "killies" (which is not a killie but a livebearer as Gregg very correctly pointed out) in the same tank as the Glass Catfish. If not, the Glass will become severely stressed and won't last long. This species is very timid and may withdraw to the point that it refuses to eat and wastes away. You have a decent sized group which is a plus, as this fish needs the company of their own.

Byron.

Hmm, I am surprised the little formosas are picking on those glasscats. But I was just in the LFS today and they have a group in a display tank . They are fragile looking fish indeed! I guess even the smallest most innocuous fish will pick on something even more delicate.
Good luck catching those little buggers. You could just put them in an unheated 5-10 gallon or equivalent if you need an excuse for another tank...

Yeah, I think they would be fine with the Betta and she may get occasional snacks from the fry.
The fry are not too hard to net provided you can spot them but hey get smarter and elusive as they get older. I still have a couple or more formosas in a 20 gallon tank several weeks after trying to net them all out.