Black marks on Tetra tail fin !!

[swackett]

Hi,

I've noticed a few of our lemon tetra's have these grey/black marks growing on the base of their tail fins. We tried dosing with an anti-Internal bacteria product that seems to have made no difference. The effected fish are still swimming around and eating, however their colouring is now a little dull compared to their tank mates.

Could it be old age? Some of them we have had for 18months now (now sure how long Lemon Tetra's live for).

Does anyone know what it could be or how to treat it.

 

[beeky]

I don't know what the black marks are. Are they flicking at all?

I've had lemon tetras for 4 or 5 years so I don't think it's old age.

 

[swackett]

No I have not seen any flicking, they seem to be behaving normally - Still going mad when they get fed!

Its seems to be growing on them, if you look down on the fish you can see the area is slightly fatter.