Disappearing Threadfins

[Ch4rlie]

As title says, there has been some mysterious disappearances of my Threadfin Rainbowfish!
 
More specifically have had 4 Threadfins disappear over the last 2 months or so.
 
No evidence whatsoever of whats happened to them, no body, no bones, nothing.
 
Water parameters, ph, 7.8, amonia 0, nitrite 0, nitrate between 5 - 10 ppm.
 
Water changes about 35% weekly.
 
Have live plants and a couple pieces of bogwood.
 
Water flow is fine, filter intake is covered because of red cherry shrimps, so nothing would be sucked into filter.
 
Also have assassin snails.
 
Now, my thinking is, if a threadfin died naturally or from whatever possible causes, the RCS and assassin snails will easily take care of the dead fish no problem at all, hence no body or bones.
 
However 4 fish in 2 months or so seems something is amiss. its not water parameters, doubt anything in tank set up would do anything since pretty much exactly the same since first set up.
 
Also suspect a few adult shrimps have disappeared as well, as there are very few males left, as I distinctly remember at least 4 or 5 of them a few months ago as they hare around the tank when females are berried!
 
My gut feeling is it COULD be a damselfly nymph since i had 5 damselflies removed in the past when first set up.
 
http/www.fishforums.net/index.php?/topic/424490-damselfly-nymph/
 
Could it be one of these again, i have searched thoroughly for one of these and have not seen one otherwise would be removed pronto!
 
AM really scratching my head over this.
 
Ideas?
 
EDIT : Forgot to mention, tank is covered so no jumpers.

 

[DrRob]

First up, sorry for your losses.
 

tank is covered so no jumpers.

 
I've thought that before. It's amazing how they can find a way. I've thought the same with filters. I have no idea how some fish have made it into filters through holes far smaller than they are.
 
Otherwise, losing stock would suggest that either conditions aren't right or a predator. Threadfins aren't exactly tiny, so it'd have to be something of size, so a nymph would be an option.
 
Personally, I'd have a good water change and have a good search of the the tank while the water level is low.

 

[Ch4rlie]

Thanks for the input DrRob, have just thoroughly checked all around the tank ground area, no dead fish remains at all.
 
I do have 2 small diy gaps in lid for the filter pipes so just checked to be sure.
 
But to be honest doubt it was jumpers or water parameters as shrimps have not shown any signs at all anything wrong with water parameters, and i do test every so often, no changes at all.
 
These damselfly nymphs.......

 

[DrRob]

There is always the oxygen demand thing with larger creatures. Essentially, the bigger you are, the more oxygen you need, so sometimes a small critter may escape a problem while the bigger stock succumb. Could potentially happen heavily planted, especially if there was a pocket somewhere in there of something breaking down. Any random holes under some decor that something could have crawled into and died?

 

[Ch4rlie]

Certainly a possibility.
 
Am thinking going to re-home these threadfins this weekend before lose anymore.
 
Then get a small 15 or 20 gal tank and transfer the RCS and assassins to that, instant cycle using filter media so should be ok.
 
Sounds drastic but am going to be moving house soon and was planning on doing this but not this soon though but has to be done sooner or later anyway.
 
Might find the answer once have removed plants and decor etc. 
 
Just frustrating more than anything really.

 

[Baccus]

Are the shrimp acting nervous at all and hiding all the time or are they out and about stuffing themselves with food like they usually do? If the shrimp are acting nervous then I would agree a predator like a dragonfly nymph has got into the tank. I had a pack of them nearly eat my entire chocolate cherry shrimp program, it was only the dwindling shrimp numbers, lack of new shrimplets and the hiding shrimp that gave me the clue that I had unwanted guests.
 
For the disappearing threadfins my money would be on that they died of either predation (and any leftovers where cleaned up by other tank scavangers) or that they died of old age. I am pretty sure that threadfins don't have a particularly long life, and if you got yours already mature there is no way of knowing how old they where. And once again an elderly fish perhaps dying and its corpse getting pushed to a hidden corner of the tank could easily be cleaned up in less than a day by snails and shrimp. I have seen ramshorn snalis strip a huge female guppy in less than 8hrs, so a thin bodied and only 5cm threadfin would take even less time to disappear.
 
As Dr Rob said it could also be down to a lack of oxygen issue, all of my tanks that are fairly heavily planted also have airstones in the furtherest corners away from the filter, just to help keep water movement happening in all areas of the tank.
 
I hope once you move and settle in your new home that you try the threadfins again, they are a great fish, even though impossible to get a good photo of. I just got some more boosting my numbers up to the 16 mark and they are schooling with 6 pygmy rainbows, which makes for a very active and colourful display.

 

[Ch4rlie]

Baccus - great response and thanks for taking the time to write that out.
 
Shrimps are pretty much doing their normal behaviours although i have not counted them so cannot say for sure if dwindling numbers due to how many shrimplets there are!
 
It could be possibly down to old age but kinda doubt it, but difficult to tell really as no tell tale signs as to age.
 
Lack of oxygen is a slight possibility but my tank is over filtered and plenty of surface agitation with spray bar and decent flow over thaw tank, its only a 90l so not a big tank. 
 
Is there anyway of telling if water is under oxygenated?
 
And predication is also likely but have not seen any signs of any nymphs and consider myself pretty good at spotting them, maybe this one is super good at hiding?
 
As for setting up with thread fins again when i set up once have moved and settled down, i love these guys and gotten to know their behaviour and traits and flaring is cool to watch, its a possibility but will see how it plays out and what i fancy doing.