Safe vs. Unsafe Feeder Fish
With one of their primary prey items being small fish, you may consider picking up some feeder minnows from your local pet store to offer to your Dragon Snake, but unfortunately, this particular feeder would do much more harm than good for your snake.
Many of the commercially available feeder fish (such as minnows and shiners) contain high levels of an enyzme called thiaminase. This enzyme breaks down thiamine (vitamin B1), which is crucial for all living things to function and grow. Thiamin deficiency destroys cells in the central nervous system, and can result in head wobbling, stargazing, incoordination, convulsions and even death if left untreated. That said, there are a few safe options for feeder fish out there that are readily available and of perfect size to feed your Dragon snake, such as Mosquito fish (Gambusia affinis), Guppies (Poecilia reticulata) and Platies (Xiphophorus maculatus). I recently grew a preference for feeding mosquito fish, but whichever one of these options works best for you and your Dragon snake will do just fine.
If you would like to learn more about thiaminase and which fish contain them, you may do so here.