The Whopper in Monster Hunter Wilds, as mentioned, can include either the Gastronome Tuna, Great Trevally, Gajau or Goliath Squid. Bring any of these back to Kanya, and you'll have completed The Catch of a Lifetime. Before you start fishing for Whoppers, use the Tuff Joint bait which lures in the most common Whopper variants.

This is a guide for locating the Goldenfish from the "Fishing: Life, in Microcosm" side-quest in Monster Hunter Wilds.

Here's a list of Monster Hunter Wilds fish and where to find them, including the Goldenfish, Gravid Bowfin, Whopper, and Grand Escunite.