# Disappearing Danios



## SandstoneSturgeon (24 Mar 2016)

I have a very unusual mystery that is beyond my skill level.  I have a 260L tank with an API Filstar canister filter.  Tank has been operational for about a year now and was originally stocked as follows:

4 Giant Danios
9 Longfin Danios
6 Black Neons
9 Glowlight tetras
5 Emerald Corys

Plants:

Water Wisteria
Java Ferns  Argentine Swords

I noticed 6 months ago that my longfin Danios were dwindling in numbers, from 9 down to 1!  I would search the entire tank for bodies and never found any.  Nothing ever turned up in the filter and I have a tight fitting lid.  Last weekend I did a rescape (pics coming ) and completely changed out the gravel for some CaribSea complete.  Never found even one dead Danio.  Are they getting eaten by the giants?  It seems unlikely that 8 of my 9 longfins would be eaten but the much smaller and much slower swimming tetras are all still present and well.  Can someone tell me where these little Houdinis have vanished to?

Thanks for your help
James A


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## SandstoneSturgeon (24 Mar 2016)

Could the Cory's have eaten the bodies before I had a chance to find them every time?  I wouldn't even know what was killing them in that case.


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## PARAGUAY (24 Mar 2016)

Is it a opened top tank?Danios notorious jumpers ? I  have very old Black Widow that as just passed away have removed bog wood etc to try and find unsuccessfuly just now,so am doing daily water changes and increasing filter maintainence at moment


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## Aqua360 (24 Mar 2016)

probably eaten fast, those smaller fish don't tend to leave much residuals after they get eaten at the bottom


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## Tim Harrison (24 Mar 2016)

Probably eaten and/or jumped. Do you have a cat? If so it'll probably hoover up any jumpers as well, thus leaving no trace.


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## SandstoneSturgeon (24 Mar 2016)

Tank has a tight fitting lid because of the giant Danios and no cat (landlord won't allow  ) so it looks like they died of something.  All the other fish look very healthy and well so I'm wondering now if there are any diseases that would be specific to only them?  They all appeared very healthy up to the point were they went missing but I guess that doesn't always mean they are well.  Water parameters all seem good so the only other thing is maybe the hard alkaline water?  All the Midwestern US has very hard water that is fairly alkaline.  I use Sphagnum Moss in my filter to try and make the water a little more acidic and temporarily soften it up.


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## alto (24 Mar 2016)

SandstoneSturgeon said:


> Are they getting eaten by the giants? It seems unlikely that 8 of my 9 longfins would be eaten but the much smaller and much slower swimming tetras are all still present and well.


I'd expect aggression to be focused on conspecifics - in this instance the longfin danios - so not really surprising that the neons & tetras are "ignored" (likely they don't give the same "feedback" re behavior as other danio species) ... you don't mention tank size but it's generally recommended to keep 'Giant Danio' in groups of at least 10
- though if yours are peaceful, then perhaps just maintain the existing group & avoid adding other danio species, especially long fin variants which are definitely not as robust as the "wild type"  ( + those fins often attract attention from other fish).
While the Giant's may not have eaten the smaller longfin danios, they may have stressed them, making them much more susceptible to "disease"  - not something that will spread through your tank but the sort of chronic condition where fish just don't thrive & numbers gradually decrease, until some months later few or none of the original group remains.

It's very usual to not find a body, often fish will go into "hiding" when unwell, deterioration is very quick with fish (re specific biology) & a fish that dies late evening will often be "gone" by morning - other fish are generally rather quick to find this tasty snack 




SandstoneSturgeon said:


> I'm wondering now if there are any diseases that would be specific to only them?


This also has merit - Matt mentions this in his Seriously Fish article, also read through notes at the end of article ... it seems likely that you would've noticed some symptoms though 



> Unfortunately it has been mass-produced in huge numbers for many years, thus inbreeding has occurred on a large scale and quality stock can be hard to find.
> 
> Alongside morphological deformities common ailments include ‘neon tetra disease’ (NTD), caused by the microsporidian parasite _Pleistophora hyphessobryconis_ and basically untreatable once it reaches an advanced stage.
> 
> ...


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## SandstoneSturgeon (24 Mar 2016)

Sorry about not posting the dimensions.Tank is 121cm long, 30cm wide, and 76cm tall. I had been concerned about putting too many giants in because of the size, do you think I could add more giants? I really enjoy their energy and hyperactivity.  

Interesting that the article that was posted by alto (thanks for sharing that, btw.  I've favorited it and will look to sign up ) mentions that, zebra Danios do not favor strong currents in the wild.Their counter parts, the giant Danios, love to swim into the strong current that I have set up with my canister filter. The upper half of the tank has a good swift flow for the giants and the lower half is protected with lava rocks to provide calmer waters for the tetras. Danios like open spaces to swim and mine always hung out at the top. I,wonder if that strong current stressed them?


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## alto (24 Mar 2016)

Seriously Fish is an outstanding site (referenced articles!)

_Devario_ _malabaricus_ your "giants" may be this species (I suspect the max standard length given is an error, 15cm is more usual SL listed) - if you put "danio" into the SF search engine, lots of interesting species  



SandstoneSturgeon said:


> Danios like open spaces to swim and mine always hung out at the top


I wonder then ... Zebra danios are renowned for their adaptability, it's unlike them to not integrate into a tank
- either disease or aggression from the Giants would account for this behaviour: once the subordinate fish have been trounced, often all it takes is a fin flip from _the Boss_ to keep them in place, so it's not unusual to observe very little to no chasing or signs of aggression

How many Giants you can keep depends on your filtration & water change routine - how big are your present group? not overfeeding is a significant factor in bioload.
If you net search, you can find several discussions on keeping this fish.


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## SandstoneSturgeon (25 Mar 2016)

My four are fully grown.  The smallest is about 4.5 inches and the alpha boss is probably a little over 5 inches.  All discussions that I read suggest a group of at least 8 for peaceful results.  Might be time to add a few more of the giants.


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