Adaptability varies between animals, even within families and genus. Plus, it is usually a complex matter, e.g., adaptability may be enhanced or reduced by water hardness, chemical composition, current, turbidity, substrate, diet, oxygen levels, etc. and these may have an unpredictable effect on the how a fish handles a long-term temperature change. You know, e.g., synergistic and antagonistic effects, etc.
What you are thinking is an experiment that likely has no answer yet.
Who farms wels and for what purpose? They are too slow growing and too cannibalistic to even be remotely considered for food fish farming. If for restocking the areas where they are in danger or for stocking new areas, then yes, but I cannot imagine this to be large scale and unless the new areas are hot, there might be no reason to raise them at higher temp than the yearly temp and cycles they have evolved in.
I seem to recall vaguely that some wallagos are raised but why and how, IDK either. If they are, those conditions would apply more directly to your experimental prerequisites. In other words, adaptability of wels does not translate in that of wallagoes.
