would it be safe to put either an oscar or a jack dempsey into a tank with a temperature of 71 degrees? my jd is bullying my new oscars and i dont know if i can wait til i get a heater to put them in my new tank.
i doubt anyone could really answer that question.. but either will survive in there well enough. The only problem with keeping such fish in 71F is that you have increased chance of disease outbreak; they won't actually drop dead on you, or anything like that.
For about a day he should be fine in there, just dont take him out of the current take and jump him in the 71F. Take a bucket and fill it up half way with the current tank water and put the fish in there and slowly keep adding the water from 71F... try to spread that procedure to about half an hour and he should be fine.