Animal Crossing: New Horizons has a total of 80 fish that players can catch, and some fish are much larger than others. The simplest way to tell a fishs size is by the shadow they leave in the water; small fish will cast a small shadow, while the biggest fish available in the game will cast the biggest shadow. Finding the bigger and rarer fish takes patience, as certain conditions must be met in order to be caught, which means some players may spend hours or days searching for a single one. The good news is, some of these big and rare fish will be worth a lot of bells.

https://screenrant.com/animal-crossing-new-horizons-biggest-fish-shark-sunfish/