Zebra Danio... Old Or Sick?

For the last few weeks I've noticed that one of my danios has become very slim, is almost transparent, has developed a bent spine and it looks like one of it's gills might be damaged. It's still attached about looks to be 'pushed' in. I'm assuming that it may have gotten into a lil scrap with one of the other danios. I do see it getting picked on a bit more now. Maybe it's due to it's feebleness.
I wanted to preform a water check but have run out of testing supplies so I won't be able to give that info until I can make it to the store.
They are in a 20 gal tank (roughly 18"h x 24"l x 12"w), holding strong between 22 to 24C, with the following tank mates.
6 zebra danios (1 to 2 years)
1 bristle nose pleco (3 to 4 years)
2 julii cories (2 years)

Does this look like it might be old age?
I don't notice any worms, fuzziness/whiteness, isn't acting weird or anything else out of the ordinary aside from the above.
I've attached a few pictures.

Wow he's in bad shape.
It sounds like old age, they only live for up to 2 years. The spine can bend and go thin in old age.

if cared for properely danios should live up to 5 years.
i had a lot of zebras go the same way as yours, turned out to be fish tb

Never kept danio spishkey. Just going by this danio article.
http/www.aquarticles.com/articles/breedi...bra_Danios.html

sorry wilder didnt see your post before i posted i do believe they can live up to 5 yrs, my oldest are 3

heres a good site that tells you expected life spans of a large range of fish

http/freshaquarium.about.com/cs/beginner.../a/lifespan.htm

Thanks for the link spishkey.

Thanks for the speedy replies and helpful links.
I was hoping it would be old age (of all the things to hope for!). I think it's more likely to be that then anything else right now. I see no signs of illness or disease in him or any of the other fish.
The others are still picking on him a bit, so he's in a nursery til he gets better or parishes.
If he makes a miraculous recovery, I'll let you know.
Thanks again!

Good luck.
Sadly fish will pick on sick fish.