2) In fact, they aren't catfishes. Belong to a big family of mainly marine fishes called gobies. Totally different orders. Should be named climbing gobies.
3) They do it for the same reason as Salmons do: to reproduce in freshwater.
4) But unlike salmons they don't swim or jump. They climb the slippery rock wall like a freestyle climber, using the suction cups in their belly that gobies have (pelvic fins transformed), and their other fins and tail to propel
5) Somebody filmed those fishes climbing.
These species are "restricted to fresh water in South America" source: https://en.wikipedia.org/wiki/Pseudopimelodidae#Distribution
And this is a good environment in which evolution could progressively improve rock-holding and climbing ability.