Tropical Fish Won't Spawn in Oceans

When I search through lukewarm and warm oceans in minecraft, and in reefs, I can't find any tropical fish. I used to find many in this one reef, and it was my location for collecting fish. I have created a fish store in my game, so I have a lot of fish on display currently. I still need a lot more, and not being able to find any tropical fish for the store is quite annoying since I've spent forever building the store.