What keeps killing my Tetra ?

[Ansorgii]

Since a few weeks, something in my Tank keeps killing certain Tetra, and I struggle to figure out what it is.

At first it started as the occasional rummy nose disappearing, but after I recently added 30 small silvertips, ~15 disappeared on the first day (not night) and now after 2 days only 8 are left.

However, not all just vanish, I regularly find their corpses if they float or get stuck to a streampump, and they are always bitten in half with the frontpart remaining. This morning I fished out these 2 in the pic.

My overall stock aside from the rummy noses and silvertips is:

6 baby Retroculus
2 L14
a few L333 or 270
2 unknown L cats
20 Lemon tetra
A bunch of guppy
60 goldline Corys
2 medium Oxydoras Niger

While some sources on the internet say that Retros may eat small fish, I have yet to see them chase a fish or not struggle swallowing a pellet larger than 2mm. And if they ate 15 in one day they would burst. And I don't know how they could bight of with their Mouth.

The Niger are also harmless, they show no interest in living or dead fish, everything that isn't a pellet gets ignored. And if they would eat them they inhale them at once.

I am very certain that the Corys or Guppies aint it either. Strangely the guppys keep multiplying and even the babys do not get all eaten. But they also do not sink during the night.

The only fish able to bite off are technically the L-cats and Tetras, but could this be ?
A few years back I had Chalceus that figured out they can do as piranhas, and shredded all tetras and even some Heros often leaving the front part behind.

I know there is also a chance that they just died and then got eaten on by other fish, but other dead fish were not chewed on, and not halfed.

Its not the streaming pump either, since they cant fit in the slits and the night I left them off was a lot more deadly.

Do you guys have any ideas what it could be ?
I really struggle to figure it out. My biggest suspision currently are the lemons since they had no losses so far and they might dislike silver Fintips, but I cant back that up at all.

 

[duanes]

My guess is it's the Oxydoras. (How big are they (in inches)?)
At maturity they will get 3 ft long, and eat every fish in your tank.
Because they are generally nocturnal feeders, you would not see Oxydoras chasing fish during the day, and chasing would not be the technique they would use to capture prey like tetras anyway.
Tetras are too fast and aware during daylight hours, when awake, but at night when at rest, and semi-conscious, an Oxydorus could easily sneak up, corner, and capture them.

Retroculus prefer small foods like insect larvae, and mollusks they sift from the substrate, and are also inept at predation on quick fish like tetras.

 

[Ansorgii]

Currently they are 15-16 inches, a friend of mine had one that reached 5 ft, but that was an exceptionall behemoth.

Like I said above, they vanished during the day. All the pellets in the world won't make mine move if there is any light in the room unless they are very hungry. And if they would, they would just swallow them hole. As far as I am aware they do not have teeth either, so I can't see how they half them.

I don't think that they will actively eat fish either, for a long time it was just them and rummys and nothing happened, and if a dead one lays around they ignore it. They are not predators, more gigantic eartheaters. Most people have them as a cleanup in their Tank and train them on dead fish, but their natural diet is more towards invertebrae and dendritus. If a fish ends up in their mouth they might eat it, but so far they showed no sign of trying to make it happen. I spied on them at night, they test everything with their barbels, and whenever they hit a fish with it it swam away while they showed no reaction. Hell, during the day my corys "cuddle" with them, I really can't see them as predators.

They are the complete opposit of every pred. cat I ever had (except limas), they would strike at everything that moved, and try to eat fish to big to fit.

 

[Iwhoopedbatman]

It's possible they just died and the plecos gnawed at their bodies.

 

[jjohnwm]

I dunno...when a fish dies and is then gnawed on, it usually looks like a thoroughly-chewed three-year-old dog toy. These fish look like they were chopped in half using a cleaver; pretty clean, smooth edge.

I know nothing about pleco-type cats, but I do recall reading that some species are very carnivorous. Any chance that one of those L-numbers you listed is a wolf in sheep's clothing?

I don't think it is the Niger cats; at the size you describe, they would indeed just gulp these fish down whole if they were so inclined. And the big Niger that belongs to a friend of mine absolutely refuses to eat even the smallest fish that are kept with him.

 

[Fishman Dave]

Eating tetras through daylight.
From the list you have provided and the pictures my first thought is that you have someone else in the tank not on the list.
Never kept retroculus but the behaviour would seem strange for them, although young fish often show behaviour not normal for parents as they grow and learn and this may be an opportunistic feeding if they have not learnt from parents.
The bites just look from a larger fish but I would also rule out the Niger, the plecs and pretty much the rest of the list.
By 2 L cats, you do mean 2 unknown L number plecs? And not something else we are not considering?

 

[Ansorgii]

I Iwhoopedbatman while that can always happen, gnawed on fish end up as a deformed mass, not a relatively clear cut half. Today I found a half one that was gnawed on, it just desintehrated fully as I tried to pic it up.

jjohnwm while there might be a pleco hunting them, I think they would end up like that chewed toy you mentioned. And nice to hear you know a bigger one that is also not a pred.

Fishman Dave They look like a chalceus or Silverdollar bit them in half. I removed my Myleus a few weeks ago since they scared most of their Tankmates, and it did not stop.

I don't think Retroculus even have the biteforce to half them, certainly not the teeth.

I mean 2 L plecs that I don't know the number off, nor anyone I asked so far. I put a pic up, but its not a good one since they gained some more mass (shape) afterwards and are actually more grey-white-greenish. They used to be very shy, but are now fairly active after I added other plecs.

I tried to catch out the remaining silvertips and put them to my baby cory. They are fine there.

2 remained in the main tank, of which I found one halfed and gnawed on this "morning". Another rummy went missing aswell.

The largest loss at once happened while the light was on. However I can't exclude the night fully since due to the sun rising early the fish get active 2-3 hours before I wake up or turn the lights on, which is when I sometimes find a halfed one already, like today.

What makes me the most suspicios is that these fish are neither the smallest nor most numerous, and that they get exclusively eaten from behind. It really reminds me of my chalceus that started with a bite in the tail and then swarmed the poor fish until it stopped moving, often leaving the front. But they left a symmetric cut, while these always have a diagonal to them if you look from the top.

I will put some Lemon tetra to them to see if anything happens, but I don't know of much to do else. Watching the tank for hours gave me no result so far.

 

[Fishman Dave]

Look like L340 mega clown but hard to tell

 

[Backfromthedead]

Hmmm the way the fish are cleanly chopped in half is suspicious to me. Any chance these fish were gravid females and a previously uninterested tankmate took interest in the tempting egg sac? I have observed this in my tank with gravid lampeye tetras and pictus cats. When the females fatten up they disappear quickly thereafter, though i cant say ive ever seen any remains left behind.

 

[Ansorgii]

Interesting observations, but these were still babys, and all but one are gone now, so I don't think it could have been that.

I am thinking of buying a few and larger from another store to see what happens. But it's playing with life.

Currently I am trying to catch the lemons and put them to the remaining silvertips to see if anything happens, but they are a pain to catch as they wake up instantly at night and there is no chance during the day without destroying my tank, so its a slow process.