I have about 8 glass catfish in a 30gallon tank. The majority of them have been with me since day 1 which was over a year ago. I pretty much know how they move and what they do at different times. However, I now have one catfish that is acting weird. While the others are swimming in the current, this one is swimming at a higher angle, close to being vertical. He will quickly sink to the bottom and it seems like he may be struggling at times, but he does get back to the top. His body is still clear, no signs of any discoloration inside HOWEVER his head portion is turning a little sand colorish. None of the other catfish have this color on their heads. His whiskers are pointing how they always have and the same as the others.
My question is, is this just old age? How do you tell that your catfish is getting old? How long are they expected to live?