Very interesting. Hard to fathom the 215 yr. carp story. Constant supply of fresh water with no chemicals. Sounds like a drip system would be a good investment for long term keepers.
i have my doubts about 200 year old koi. it is probably closer 80-100. fish can get more than one ring on scales per year. plus i have read that it was not uncommon for gardeners to switch koi when they die for identical ones so that their master would not notice their death
lungfish are fairly inactive if im right where as rays are very active and carp tend to live in cooler waters if im not mistaken and its been sugested that some go into a "hibernative" stage so this would sugest to me that they would live a longer live than a more active fish, especially if the active fish was in warmer water.
my biggest ray is a 20" female marble motoro i dont know how old she is though unfortunatly but im sure feeding and temperature hav a massive difference on size just as with any other fish kept in cooler water with less food would have.