I think he meant that you could keep an oscar in a 40 as far as water quality gors he could do wcs everyother day. I dont think any responsible hobbyist would advocate for that. But justarn is right someone might see that comment and think it was ok to do such a thing.
What about putting the fish you have in the 75 and figure out how to stock the 40 breeder. Probably add a mid size fancy pleco to the 75 too.
I wouldnt make the same mistake twice though. 75 would be a bit too small for a jag. If your heart is set on this then maybe look into a loisellei
I understand the 40g comment, I just mean I wouldn't personally choose an Oscar for his 75 either, I just find oscars are extra upkeep compared to other breeds unless they are in really big tanks.

