Fish Minigame Findings

Fish minigame
The game is agnostic to which fish is which: it only cares about the "score". That is, 1-0 and 0-1 are equivalent.
When you drop a fish, both fish swim to it, and whichever is "closest" (can be arbitrary) after the ~1 second cutscene will eat it.
The game substantially favors a larger fish to eat. When the score is 3-0, the big fish almost never loses.
There is an RNG aspect to the minigame: Upon dropping the fish, your actions can affect the outcome. For instance, since moving Link affects RNG, it is enough to change which fish eats. The takeaway isn't that you should try to manipulate it, but rather just noting the random element.
The fish swim in "cycles". They swim around in a circle about 3 times, then stop for about a second. And repeat. Being stopped affects the chase, and makes that fish less likely to win.
After eating, a fish will stop for a second. This makes it much less likely to win if another fish is dropped in immediately after.

Recommended strategy:
Drop the first fish immediately. This is because it is always equivalent.
Drop each remaining fish right after the big fish starts moving again. This qualifies it to be more likely than not to win (since it's bigger).
The 2nd drop is the most crucial, since as the fish gets bigger, the more likely it is to win.

Good luck!