Q: I love DT bettas and have been hearing that you can breed two DTs together, and that you cannot because its bad.  So which is true?

Question submitted by Conor, Glenview - IL

A: Well Conor, as I said a few days ago, breeders all have different opinions about almost everything. Ask one and he/she will say it is OK to breed two DTs, and ask another and they'll say "No way Jose!". But you come knocking to the right door because, just like you, I also LOVE DTs (and always have). In your endeavor to produce DTs, here are a few things to know (and to lookout for):
bulletDT genes improve finnage. A ST betta carrying DT genes will have a better dorsal and generally speaking, better finnage. All my lines carry DT (or just about) for that reason. Also I like to have both a ST and DT version of each line whenever possible.
bulletDT bettas have a huge dorsal and two tail lobes. They also have shorter bodies than their ST siblings. They can look a bit more stubby, as the body is not only shorter but also a bit more wide. 
bulletBecause they are shorter, DT have less space for internal organs. Usually does not cause any problem unless you overfeed. They are twice more prone to swimbladder problems than ST.
bulletDT almost never blow their tails :). ST with large tails (HM) almost invariably do (sooner or later LOL).
bulletDT bettas can come out with bent spine, or pinched peduncles, or crooked bodies. This is more predominant in recessive strains because they are more inbred. When breeding to produce DTs, expect to lose a percentage of the spawn to slight deformities. BTW, ST also can have similar problems, but it is less prevalent. 
bulletBreeding two DTs together will cause the bodies to get even shorter. Each time you breed two DTs you shorter the bodies farther more. Results? Short stubby bodies, thick, and a lot more chances of deformities (crooked spines, etc). That is why a smart breeder will avoid this combo at all cost. 
bulletThe best combo is to cross a ST carrying DT to a DT betta. You will get 50% of DTs and 50% of nice ST carrying DTs (with nice dorsals and better finnage). Almost all my lines have such characteristics. Notice that I never pair a DT female to a DT male, instead I will send a DT male with a ST sister carrying DT. I was one of the first breeders out there to sell bettas paired like that. Used to be that breeders would sell ST pairs or DT pairs, the DT pairs comprising of two DT bettas :(. So people would have to buy two pairs (one ST pair and one DT pair) to be able to get that DT to ST/dt combo. In an effort to save people money, and because I wanted people to get the best results possible, I started pairing up bettas the "right way" and selling all my lots paired that way.
bulletHowever, what if you are in a situation where all you have are two DT bettas? For example, you get a spawn of blue bettas and in there are only two purple with green fins bettas (doesn't exist, I am just trying to make a point here). These two SUPER RARE bettas should be bred together to increase the chances of getting more like them and so to not forever lose this chance of having a new color created. You will breed the two DTs together, and you will be OK, for the most part most of the fry in the first generation will be OK. But this is only OK, as a one time deal and in desperation LOL. Then you would have to cross back to ST blue siblings (hopefully carrying the same genes that caused the purple/green mutation).

To create new strains, and to maintain them (as to NOT LOSE THEM) you sometimes have to compromise and in that respect, breeding two DTS is totally acceptable. Just understand that you will have to cross back to STs soon if you do not want your line to produce nothing but deformed fish. 

I hope the above has helped all of you out there who love DTs.