Stainless steel - its worth buying a stainless steel bar or tablet, sometimes called stainless steel soap; these are sold for removing garlic, onion and fish odours from the hands. All you need to do is put your hands under running water for a minimum of 30 seconds, rubbing the bar all over your hands and fingers at the same time, with or without soap, doesn't matter. I imagine plunging your hands in the river or whatever you're fishing in whilst using the bar will work too. Any stainless steel object will do though, its just easier to use the soap tablet shaped bar - I used a stainless steel ladle in a friend's house once after chopping garlic. They definitely work for garlic, never tried it for fishy smells, but they are sold for that purpose too.