Oldest is my 10 year old marine beta. I bought from my lfs as some one traded it in around 4". It has survived 3 moves, 2 houses , and a power outage a few years back for 3 days , the water temp was in the low 50's
I have a marine Betta for 10 yrs, that I got from a friend that was moving and had it for 7 yrs...have rarely seen him eat, but he must be getting something!
Oldest fish is my 18 year old percula clownfish that I just recently gave to a friend cause his mate past away (black and white misbar clownfish that I had for 19 years)
FW - my 20" long Gibbiceps Pleco 'Murray' 15+ years
SW - My drop-dead beautiful Yellow Tail Coris 'PITA' 7 years and My Purple Tang "Freckles' that I got from Mike Slama... IIRC he had him already when I first came onto MR.