Actually...you shouldn't do that. There's a sticky on the topic somewhere around here, but the gist is, once you take it home, it's yours forever.
The main reason is that animals can pick up exotic diseases in captivity, and if they are released, carry those diseases to the wild populations. This is especially a concern with amphibians; captive Xenopus are thought to be a major vector of Bd, and some extremely virulent strains of Ranavirus have showed up in bullfrog breeding operations.
Plus, it's illegal!