OK, since there has been some negative doggie stuff, this is not.
I recently bought some fish treats for Knuckles. They are a Skate Tail and Shark Back Bone. I will say the skate tail is the first thing to really slow him down. He literally walks through EVERYTHING I give him. (braided bully sticks(20 minutes 12" 3 braid), compressed raw hide, knuckle bones etc...) The only other thing to stop him is the center 3-4 inches of a femur bone.
The down side is the skate tail has some odor to it. Like a fetid fish carcass on a muddy Mississippi beach in August. It is strong, but he seems to be puzzled by the skin texture (sandpapery) and the flavor. I will take it away after 15 minutes. Some oder will linger with him. So glad he is trained to eat bones on a waterproof rug!!! Can't imagine having to get that drool out of a carpet.
The shark back bone has a much milder odor and he has to actually chew on it for a few seconds before biting right through.
For the future, I see the back bone as an option, but so much of the skate tail.