Leaping salmon is a fish which requires 58 Fishing, 30 Strength, and 30 Agility to be caught, providing 70 Fishing experience, 6 Strength experience, and 6 Agility experience. It can be caught at Otto's Grotto or Mount Quidamortem with a barbarian rod and suitable bait after starting Barbarian Training.
It cannot be cooked but can be used with a knife to cut it open, which always gives roe, and may also give fish offcuts, providing 10 Cooking experience. The roe and offcuts serve as bait, so if the player has a high enough Cooking level, they can save some feathers. However, some players find that dropping the fish is faster and easier.
The order in which bait is used first is as follows: bait, offcuts, feather, roe, caviar.
For an exhaustive list of all known sources for this item, see here