OK in the last3 week I have been doing a LOT of reading on the Paradise fish. I love this fish but becouse of it temperment have not been able to keep one with out tank issues. From what I have read these are a true cool water fish. They color up better, stay peaceful, and will breed better. I even found sites that say they can live in 2 gal bowls better the Bettas! (I do not think I will go there, just sounds way to small)
From what I have read the paradise go into breeding mod when the temp goes up. This would be why a Paradise fish in a heated tank hates every one. I talked my LFS tuesday into puting half of there shipment into a heater tank and half into a cool water tank. The cool water tank had less agression(none that the works saw), with no injurys. Also they colored up fast and sold faster! The heated tank had the normal fighting and they still have 6 of the 10 they put in there, The cool water tank All where sold.
So this is what I found out, what do you think?

They are not coldwater fish but are sub tropical. I suspect the ones in the coldwater tanks got sold to people with bowls & no heaters wheras the tropical buyers with community tanks would possibly have known of the Paradise fish's reputation as a nipper.

I am sorry I do not see why who buys them matters. These where in tanks side by side with no sign other then fish name. What matters is the diffrace between the color and temperment of the 2 tanks.

As was said, they are not true coldwater fish. Paradisefish are sub-tropical and, while they do tolerate cold temperatures far better than bettas, very low temps will kill them. They are not, for example, capeable of living in the sort of conditions goldfish live in.

Like you said, they do breed in higher temperatures. Again, this is an indication of their prefference for higher temps. As for reduced aggression at lower temps, this isn't simply because they don't breed - it's because, at low temperatures, as with all fish when put in a lower-than-usual temperature, their metabolism slows down and they become far less active - and therefore are far less likely to fight.

Coloring up quicker is directly linked to the reduced aggression. In a tank with aggressive fish, the gouramies become stressed and won't color up. Subordinate males also avoid coloring so as not to attract too much attention from the dominant male(s). Again, with reduced aggression and activity, this is no longer an issue.

While I see nothing wrong with keeping paradisefish in cooler tanks (though not entirely coldwater - room temperature is fine), you should consider that there are some downsides. Cold water slows down the process by which ammonia is turned to nitrate and, while there is generaly a higher level of oxygen in colder tanks, this isn't of much benefit to an air-breather like the paradise. The consequence is that, despite the metabolism being slowed and therefore need for food being less, you still may find more water changes necessary to maintain good water quality. Also, the fish won't be as hardy if the temp. is too low and may contract disease. While this is less likely with such a hardy species, it should, none the less, be considered.

Concerning the idea that they do better in small bowls than bettas - I'd actualy be inclined to agree. Bettas, in my opinion, are not all that suited to extremely small tanks in that they can easily catch infections if water quality isn't perfect. Having said that, paradisefish grow slightly larger than your average betta and are far more active - making them better suited to tanks of 20 gallons+ (though, obviously, that's not necessary). Just to clarify - by, 'betta' I mean betta splendens.

I appreciate you probably already know most of this. I just wanted to say, basicaly, that paradisefish are extremely hardy and adaptable and therefore an excellent choice for a cooler tank - but they are not coldwater fish.