I still don't understand why you think your wife did anything wrong in this situation, even something small.
You brought home a pet without consulting either your wife or the person you were expecting to take are of the pet.
After a few weeks, your daughter decides she doesn't want the responsibility of a pet and gives it away to a friend. Nothing wrong with that.
Your daughter decides not to tell you until after the fact. Why is that? Did she suspect that you would try to control her or act badly about her decision?
The fact that you were upset about this and vented here seems to support that idea, as does your comment that it happened behind your back. Why did you feel you needed to be informed or consulted? You did either of those when you brought the fish into the house.
It's as if you expect to be granted more consideration than you extend to your wife and daughter.
Me: 44 H: 44 Kids: 20, 16, 16, and 10 Together/Married: 22 years H announced he was emotionally detached and considering D: 4/4/16 H announced he is going to try to stay and reconnect: 5/1/16