Fish are supplied by Capri the Dolphin. Fish are used to fill guest orders and to craft recipes at the Sushi Stand, the Grill, the Beachfront Kitchen, and other cooking Workshops.
To get Fish, make sure that you have harvested Pineapples. Then tap on the Dolphin for the Pineapple to appear. Drag the Pineapple towards the Dolphin to throw it into the bait basket.
Level up to unlock options to put more Pineapples into the bait basket. It will take longer to collect the Fish, but will give you more Fish.
Fish appear on the bait basket when Capri has finished collecting the Fish. Tap on the basket to collect the Fish. Similar to trees, you collect more Fish by tapping on Capri’s basket more than once. To collect two Fish, tap twice.
If you want to speed up the process, you can use Gems or Sunshine.
Sunshine unlocks at level 5 and can be sent to and received from your friends. It can also be earned as a quest reward or by opening Treasure Chests at the Sunken Temple.