I got my new lens today Canon 8-15mm F4 L USM Fisheye recently.
First impression when I get the lens is it has a solid built. Upon testing a few shots, I quickly notice the USM feature on the lens which has a fast and quite focusing as compared to my Tokina Fisheye.
Fungus can grow inside a lens if it has moisture being left there for a long time. However, fungus can easily be killed if they got expose to sunlight. That said, you should use your lens regularly (every week) and rest assure you shouldn't have fungus. Shoot an object a day, keep the fungus away ! hahaha
Unluckily, one of the lens my brother own has fungus in it and I have decided to give it a try to remove it.
I shall warn you DO NOT FOLLOW WHAT I WILL SHOW YOU BELOW. DO NOT ! DO IT AT YOUR OWN RISK !
This is how fungus looks like on my brother's Konica Minolta 75-300mm f4.5-5.6