I believe KF is correct about the chemicals being released in a poorly handled fish. I see people hauling a loaded stringer of fish down the lake or across portages all the time. I think they would enjoy the fresh fish taste more if they stopped and filleted/cleaned the fish as he mentioned, and stored in a wettable canvas or cloth bag.
I hauled a clean and gutted laker down the length of Sturgeon on a 90 degree day, stopping occasionally to re-soak my canvas bank coin bag I use as a "cooler". Kept it under my seat out of the sun. Was still cold too the touch hours later when I grilled it.
I agree with the comments about properly aged/ taken venison.
Milos Cihelka, who was the owner/chef at the famous Golden Mushroom restaurant in the Detroit area, was born and trained in Europe and his place was famous for it's wild game menu. He was/is a hunter and in Europe, they "age" all their game, from small to large.
My late Dad was a life long deer hunter. He wouldn't even let me go until I could put every shot from my weapon of choice into a 9" pie plate at 100 yds offhand. He said that a true sportsman had a obligation to take his game as humanely as possible. A true hunter makes sure his marksmanship skills stay good enough to make a quick/clean kill. Sadly in this 24/7 no-time society we live in, you see guys hitting the woods for deer season with 0 range time and relying on FIREPOWER not skill to take their deer. Dad grew up during the depression. He hunted with a .22 for small game on the farm they owned. Shells cost money, which was in very short supply then. His Dad would give him a half dozen .22 shells, and he was expected to bring back the same amount in rabbits/squirrels or birds. He hunted for years with a single shot rifle until us kids bought him a lever action .35 Remington. Dad said and science now shows, a wounded animal that you have to track and kill or one that takes multiple hits before you can bring it down, often has tough "gamey" tasting meat. Sometimes the feed is the culprit, but often it's the result of the Adrenaline that has flooded its body as it flees for it's life. I'm sure the same thing happens in a poorly handled fish? Maybe not Adrenaline, but some equally damaging chemical.
I know people who say they "hate" fish, because it smells/tastes "fishy"

Then when they have fresh, well prepared fish, they can't believe how good it is