I saw my first live S. rhombeus in 1957 and again in 1971. I am grateful to Frank Glennon of the Steinhardt Aquarium San Francisco, California for informing OPEFE that the oldest known (to me) piranha in captivity is *still alive (See image at left of the actual fish). I personally saw this beast in September of 1971 when it was only 6 inches TL (= total length). After 28 years in captivity this fish was only eleven inches TL (March, 1999) when it died..
*Sad news: It was reported to me by a hobbyist the S. rhombeus discussed above is no longer alive (Sunday, August 6, 2000). It was thought the fish jumped out of the aquarium or died some other way. Reportedly, the fish died sometime in the latter half of 1999. What a sad end to fish that lived for over 28 years.