My Tetra has lost his tail

[Branch1]

I have had a tank for +/- 4 months. I ythink I have it stable uand contolled.

2 x 5 neon groups and 3 Serpaes, 3 Platy and 2 swordtail, 2 silvertip?(Very active)
1 placostomous, 1 molly the other snuffed it.
I inspect my fish dailyn at feeding including counting all of them and looking for discolouration and odd behavior.
This moring my one serpae was missing his tail completely.
he hs not been able to tell me what happened but I am comncerened forhim and the other fish.
his mobility and appetite are unaffected and there is no bleeding.
His movements are normal.

No other fish show signs of fin deterioration or damage.

Has any one else ever had this happen or know what caused it?

 

[newfie]

can you tell us the size of your tank.

 

[gadazobe]

Does it look like his tail was bitten off or does it look like it rotted off?

 

[Branch1]

My tank is +/- 78 Litres

I don't know if it was bitten off or rotted of- I do inspect he fish closely on a regular basis, every day at feeding time. There was no sign of missing tails yesterday I have a submereged filter-is it possible that the injury is trauma related to the filter? Could one of the other fish been too rowdy/ I cheked with the lfs before adding new fish to the tank on compatability and got the all clear on my community.