Zebra danio with torn tail

HI FL,

I just found one of my zebra danios in my 10 gallon tank that I thought was dead. Very shocking, since I've had these fish for over 5 months now with no problem. I took her out and put her in a QT tank, and realized her tail was pretty much completely torn off. I have no idea what it could have been...

The tank has been up and running for almost 4 months, and has a sponge over the filter. IT is stocked with:
1 male betta
6 zebra danios
1 baby bristlenose pleco
Some MTS and a couple assassin snails
Recently added: 1" freshwater crab

The betta has never shown any interest in the danios, and isn't anywhere near quick enough to catch one. Any idea what could have caused it?

 

betta or other danios. these like to nip

 

Hmmm. Can you post a picture of the tail? I suspect bullying. What do the remaining edges look like?

 

Possible culprits are the betta, crab, or other danios. Depending on the severity my bet would be on the betta or the crab. Danios can be nippy, especially in cramped quarters like this, but severe aggression is more likely the betta. He doesn't necessarily have to be faster than the danios to catch them; in a small tank he could have easily just gotten them if the were swimming right by him.

However, the crab is also a likely possibility. They are certainly known to catch fish in their claws if the opportunity arises. What kind of crab is it? I would probably recommend returning the crab to keep your tank a little more peaceful. Your danios are small enough to be caught and with bettas' flowing fins they make an easy target too.

 

Well, weighing the evidence, the tank has been up 5 months running smoothly, you introduce a crab into the tank recently, and a tail gets torn; quite obviously the crab talked the betta into it Sorry.
I've never known Zebra danios to inflict serious injury before, but then I've never kept them in such small quarters before. Space is likely a factor, but beyond that, you'll just need to keep a close eye.
Did it happen at night, by chance?------rick

 

Thanks guys. I'm thinking it's probably the crab too... The tail was basically entirely torn off, and the danio didn't make it through the night. Another danio seems to have a crooked tail, but that could just be my imagination. I'll be taking the crab back.

And yes it did happen at night I believe. Maybe when the danios are sleeping?

Not sure what type of crab it is, but it looks just like this one with one small claw and one huge one:

 

About sleeping, ya, that's what I was thinking. Any chance the injured Danio will recover?----------rick

 

oh didnt notice that last one. both bettas and crabs are opportunistic feeders. anything it catches will go down.

 

I agree with the above.

 

Yeah... the danio with the crooked tail has some mobility issues. not sure if he/she will be able to fully recover though unfortunately...

 

Sorry to hear about your danio, but my opinion is that the betta may have caused the tail damage. Clean water and a god diet heals fins well, monitor for signs of infection. Best of luck.