"Clouded this boy's future is..."
Coming from a non-goonch guy... I think that a better database would be warranted - species/suspected species, age, size, length of keeping, water parameters (hardness, oxygenation, temp, etc.), description of normal and pre-death behavior, was it de-wormed, etc...
... for both perished and surviving fish.
Once this table is filled with a few dozen rows, I tend to think the picture will become more clear. Otherwise, I am afraid it will be the case of "clouded info in, clouded info out".
As for the migration idea - it may or may not have the merit and that's why this thread was created. I've come across earnest reports of migration behavior exhibited in captivity by e.g., doradiidae and ariidae. While doradiidae may have survived (they become restless, stop eating, and swim against current for months and "do look unhappy" according to the reporters), the ariidae, that spawn in fresh and live in marine, often perish.
So calling it the height of silliness backfires
... like any calling game...
Rob has everyone's respect in part because he writes significant and serious works on goonches and others. Real articles. Almost as serious as a non-professional can do. Sure he can be wrong sometimes. All we can.