An obligatory yearly update. Both are at about 2.5' having put on 6" in the year since last update. They wrestle mouth-to-mouth plus a death roll with each other sometimes which is peculiar to see but it seems inconsequential - no damage to each other as far as I could see, despite having sharp, goonch-like teeth but smaller. They do keep separate in the opposite corners of the 4500 gal.
A video clip:
Unfortunately, since the last filming, one was found unexpectedly dead on the drain screen (hence the round imprints on the tail). No change in the feeding or behavior had been noted prior to the perishing. So this is strange. The bug I have had going in my tanks for half a year usually leads to a prolonged illness period and more or less the same symptoms, including an obvious swelling, which is absent here.
The external dendritic osmoregulation organ (see the OP photos) and the tummy must have been removed post-mortum by the ever-opportunistic vulture catfish I presume. These guys always seem to target the ventral side where there is something to be grabbed on and then ripped out. Their competition the VATF usually go for the dorsal side.
In any case, I am sure the eeltail wasn't killed.
The remaining one has been doing well so far.
So in 2.5 years it grew to 2.5' from 3"-4".
Check out them teeth too.