There's another thread about river dolphins in captivity. The boto at Duisburg were named by the public, hence Oma (Grandma), Mutter (Mother), Vater (Father), Halbstarker (Teenager), and Baby. They also had "official" names in at least some cases.
Just as a point of interest, I thought I would note the captive longevity of each individual as recorded on Cetabase. All five were captured on 19/03/1975 in the Apure River, Venezuela.
Oma, the albino adult female, died on 20/08/1975 and as such survived 155 days in captivity (5 months, 2 days)
Mutter, the adult female, died on 30/05/1976 and as such survived 439 days in captivity (1 year, 2 months, 12 days)
Halbstarker, the sub-adult male, died on 31/12/1978 and as such survived 1384 days in captivity (3 years, 9 months, 13 days)
Vater, the adult male, died on 08/10/2006 and as such survived 11,527 days in captivity (31 years, 6 months, 20 days)
Baby, the juvenile male, is still alive as of 06/03/2018 and as such has survived 15,694 days and counting in captivity (42 years, 11 months, 16 days)