It appears to ba a Water Scorpion (Order: Hemiptera; Family: Nepidae) they do look like a walking stick....
They are a predator and Water Scorpions get oxygen through long breathing tubes at the base of the abdomen. They look more like sticks than like insects. They are up to 10 cm in length. They have three pairs of jointed legs. The front pair has a set of single hooks for capturing and holding prey.
I used to get them when i worked at Petsmart too. Used to feed them guppies! They would suck out their innards and just leave an empty body floating in the tank.