Immediately, it can be said that murder is a legal term applying to humans, and that it is not applicable to non-humans.

To discuss the morality of killing animals, that is up to how you define your own morals.

My personal opinion is that it is not wrong to kill animals, for sustenance or sport. It is also not wrong to kill plants, bacteria, et cetera.

If you claim killing animals is immoral, then it follows that killing plants is also immoral, because in both cases you are ending an organisms life.