Gigas giant clam

The gigas giant clam is a sea creature you catch while swimming in the sea (dive where you see bubbles). Look for a very large shadow. In the northern hemisphere look for it in May – Sep, at any time of day. It can only appear after you have caught 80 sea creatures. Nook's Cranny pays 15,000 Bells.

Despite being a clam, this X-Large shadow zooms away very fast, after 80 catches. Dive as close as you can and keep tapping A; at 15,000 Bells it is the most valuable sea creature.