He eats the fish, leaves the skeletal remains on the shore and wanders off to die. A raccoon finds the remains and scavenges what's left. A doe stops to get a drink of water. Two hours and 25 miles later, she dies. Wolves raid the carcass.
Ravens come to feast then fly further away.
Now for the icing on the cake. This poison is chemically stable. That means that a decade from now, the ground it is spilled on is toxic. It has the ability to kill x-potentially. Thank you to North American Wolf Association for this scenario.