Zebra Danio - old age or physical damage?

[cwt]

Two 'unhealthy' posts in one week! I am *not* on a roll here.

In the 30G tank I have 3 species, but the dozen danios are the predominant one in it. The juveniles which were hatched almost 4 months ago now look like they're in puberty... instead of just waiting for food, they're now aggressively chasing the females and each other around like the adult males always have.

I think this chasing may have damaged an older danio though; it's a long-fin, that was adult when I bought it. It is floating around more than swimming, twitching its neck to one side only, and apparently can't swim in a straight line; attitude varies between straight up and straight down. There aren't any wounds or obvious disease issues on the fish.

The other fish are still hassling it too. Should I remove it to the sick tank (which is full of Maracyn for the rainbowfish, mentioned in another thread) and let it hang out there? I don't know if it's had a stroke, busted neck, or what else it could be.

Edit: water params are 0, 0, and near 0 on the nitrates... the java fern eats up most of the NO3 here.

 

[RogerMcAllen]

What is the minimum age of the fish?

Zebra danios only have about 2 years in them. After that they will often get a curved spine and die.

 

[cwt]

Thanks for the reply. I've seen that mentioned before, and wondered whether the spine curved horizontally or vertically. In this case, the head is turned about 10-20 degrees right of center, no vertical curve that I can see.

it's in the sick tank now, which has better lighting; still don't see any other visible problems. I've had the fish 5 months, and it was roughly the adult size that it is now; so I'm guessing based on the growth of my smaller ones, that it is at least a year old.