Its not that they "don't like space" its because so many betta's have been bred to have such huge mutant tails, the fish litterally struggles to live with its long tail in a large normal tank or pond environment. The same is happening to guppys as well because they are being bred to have longer and fancier tails too.
Yeah, that's why I added the "especially for long-finned varieties" part... however, I don't think that's the whole story either. I've had several species of wild betta, and not a single one of them patrols the way domestic splendens do. I think that in the process of breeding in more aggression for their use as fighters (and all fancy varieties originally came from fighters, so they retain that mentality to an extent,) the fish also became hyper-territorial... it makes sense, considering that their aggression is territorial in nature. You don't see an imbellis patrolling the tank over and over again, they pretty much just stick to their favourite areas. Sure, they'll take a look around on occasion, but it's nothing like what my splendens do. There's a pretty dramatic behavioural difference there, considering how closely related the two species are in the wild (it's still argued in some circles that the imbellis are a subspecies of splendens rather than their own species).
tokis , i wouldnt agree with you there. if having a long tail really was so "stressful" it would make me wonder why they still have such long aquarium lives (2plus years ). and , if you dont like the idea of long tailed bettas .................. buy plakats!
2 years is long? Compared to what? How often do bettas actually die from illness rather than old age, and how much does their finnage contribute to this?
Unless you know what the average lifespan of a captive wild splendens or imbellis is, what do you have to compare to? 2 years is average at best, and pretty low compared to the lifespans of many other species in the fishkeeping hobby. It may be average for the species as a whole, but unless you do a study on the difference in lifespan between wild bettas and domestic splendens and between long-finned and plakat varieties, there's no way to know for sure. That might be an interesting thesis study for someone... *coughmecough*