There is a species of catfish in Ecuador that climbs cave walls. It reminds me of how Chicagoans feel trying to claw our way up out of winter to see some sunlight.
It’s unknown why these fish, who are not adapted for life in the caves (the are not blind, for instance, and they eat algae, which requires sunlight) are even there.
I’m going to go out on a limb and suggest they are extreme sporting fish who love spelunking.
It’s either that or they are searching out new habitat before the Amazon rivers are all wrecked.
Or maybe they’re government agents seeking out the lizard people’s underground lair.
The Descent might have been a much stranger film with climbing catfish involved.