He'll eat'em eventually. As for how long one can go without food? Thats a question I can't answer with any actual experience as I've never starved one to death. However, If you can find an arowana owner that actually starved his arowana to death and he tells you that it took 3 weeks and 4 days, then I'd say the answer to your question is 3 weeks and maybe 2 days if your lucky.