There is no difference in the value of a life of a mouse, a rat, a cat, a dog, a fish, a cow or a chicken. However none of them should be killed merciless. The key line here is what purpose they are being bred for.
I would not kill a fancy rat, nor I would kill a domesticated cat or dog; I would not kill a display fish or a hobby roach. Someone's pet chicken or goat also applies here. However, I could care less if they are being raised as food items or are feral. Wildlife should also recieve protection from humans as well, unless their population are unnaturally exploding and cannot be managed by the local predators.
What we are talking about here is completely different though, some are being raised for the sole purpose of feeding people and animals, while others are raised to be a hobbyist's collector specimen or a pet.