Since they are airbreathers you shouldnt be using 100% pure oxygen as this can burn them. Aim for approx 50% oxygen by leaving some air in the bag before adding the O2. ie dont deflate the bag totally. The same applies for corydoras, labyrinth (Gourami) , siamese fighters, snakeheads etc. Most fish shops will already know this.
More important is to fast the fish at least 24 hours before travel by not feeding. You could add some chemical ammonia binders like PRIME or CHLORMON too if the fish are particularly large.