The fish was discovered on Friday morning at a house in South London.
"The real tragedy about this case" commented Detective Inspector Andrew Bacon, "is that this fish has been lying here for almost a week. If we'd discovered it just a few days earlier, it would have made a lovely fish supper."
When asked about the current state of the fish, Mr. Bacon revealed it was in a terrible condition, adding "I really can't understand how someone could do that to such a beautiful trout."
A memorial service will be held for the fish later this week.
The deceased was named as Paul Phillips.