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I purchased four Nigriventris about two weeks ago at a size of about 1 to 1.5 inches, they are now over 2 inches in size.
Could the fast growth be due to my shoal of Glowlight Tetras diminishing rapidly?

Tim,
Have you got anything else in the tank? The nigriventris seem an unlikely culprit. In all the time I've kept them, I've never seen mine eat fish, even small ones.

Even big (10-12") Synos will rarely or never eat small fish.

If your nigriventris are growing fast, they may actually be something else. This happpened to us not long ago (and we thought we knew a little bit about Synos!). We bought four "nigriventris" for $4/piece, and they all turned out to be tiny eupterus!

Dinyar

My S. nigiriventris have never eaten smaller fishes too. But my nigriventris are just about 5 cm. I think they won't get bigger anymore.

It really is quite a job to see them as they are constantly hidden underneath two large pieces of bogwood, do other Synodontis swim upside down?
They were swimming normally in the dealers aquarium and went upside down as soon as I got them home.
There is nothing else in the aquarium that could eat the Tetras, they could just be dying off due to old age.

It really is quite a job to see them as they are constantly hidden underneath two large pieces of bogwood, do other Synodontis swim upside down?

Several species spend a fair amount of time swimming upside down. That said, the fact that the fish weren't swimming upside down at the store sounds a little fishy (sorry for the pun). Sounds like you might not have nigriventris after all. Any chance of a pic so that we can judge for ourselves?

Would they swim normally if they had no cover, all they had was a small piece of bogwood they were all huddled around.
No pics as I do not have a digi cam.

I have seen <i>S. nigriventris</i> in stores where the tank was completely bare and the fish were housed in incredibly crowded conditions (this was in Singapore). They continued to swim upside down even this way.

My young Synos only swim upside down when under something and the older one swims upside down all the time, on its side on end spinning even.


Yes they do eat guppies and Tetras.

I have just been in contact with the store, the remaining Syno's have just been fed flake food and they stayed belly down.

Silurus is right. S. nigrivetris will swim upside down almost all the time, even in a bare tank. Other Synos might, but S. nigriventris are too small to eat tetras or guppies.

Dinyar

Sorry, but are there dead fish in the tank or did they disappear?
If the tetra was dead from age they would eat the body no problem.

My Nigriventis will dart around the tank right side up and upside down when I remove all the rocks during water changes.I notice if they are feeling secure(lights out)they'll swim right side up to eat food that sits on the bottom.Otherwise,they swim upside down under rocks all the time.

I reckon that there are about five or six Tetras missing presumed dead, these could have died and been eaten by the eight Ancistrus in there.
It sounds like I will have to get a picture of them, dont know how as I have only seen fleeting glimpses of them.
I do not really want to remove the bogwood as the two pieces are both 23" long and 15" high, it might be easier to get pics at the store.

S. contractus swims upside down too but is also to small to eat tetras.

True upside downers are indeed 95% of the time upside down....
I know a few LFS that have a bunch of them, and those tanks are bare, with the exception of lots of fish and a heater.
So the Syno's are hiding upside down under or against the heater, and using a few big Pleco's (including a huge Panaque 'bruno' as 'substitute driftwood' for them)

this one's one of Pectorale's having a nap....