I'm by no means an expert on gulpers, but I have a pair (7 and 9 inches) that I have kept for about 10 months now in a 75 gallon. In February, my canister filter failed and I did daily water changes of about 15% for a couple of weeks while I tried to fix the filter. During this time, the gulpers became infected with ich. Once the filter was running again, I cranked the temp up to 85 f (with a couple of airstones). I was surprised to see the fish improve dramatically over the course of the next 10 days. Since then, I've kept their temp up around 83 and they seem to be healthier and more active than before when they were at 75.
I can't definitively say they're doing better in warmer water, but I do have a hunch.
I'm also curious if gulpers tend to struggle because of some kind of water quality issue. If you look at their range, they're limited to a rather small region of South America, the upper Orinoco and the Rio Negro. Theoretically, then it has access to the entire Orinoco and Amazon drainages, yet it hasn't dispersed. There could be a whole host of biological reasons for why it's not widespread, but it could also be quite narrowly adapted to certain blackwater habitats.
I can't definitively say they're doing better in warmer water, but I do have a hunch.
I'm also curious if gulpers tend to struggle because of some kind of water quality issue. If you look at their range, they're limited to a rather small region of South America, the upper Orinoco and the Rio Negro. Theoretically, then it has access to the entire Orinoco and Amazon drainages, yet it hasn't dispersed. There could be a whole host of biological reasons for why it's not widespread, but it could also be quite narrowly adapted to certain blackwater habitats.