Sturgeon

The Sturgeon is a freshwater fish in. It is one of only three fish to spawn exclusively in the river mouth, along with the Salmon and King Salmon. Of those, the sturgeon is the only one that is in-season for more than a single month.

In
Upon donating the sturgeon to the museum, Blathers will comment:
 * "The sturgeon is a large and long-lived fish which has changed little in the last 300 million years. One curious behavior of theirs is leaping high out of the water and falling back in on their sides. The smacking sounds of their re-entry can be heard for up to half a mile away, likely more underwater! No one knows why they do it, but I like to think it's their impression of bread popping out of a toaster!"