Out of the 22 predefined/common tropical fish types I could find all of them naturally except for the Yellowtail Parrotfish.

Then I proceeded to type in a command to summon in a Yellowtail Parrotfish specifically; "/summon tropicalfish ~ ~ ~ minecraft:become_yellow_tail_parrot" and got a white kob fish (the generic fish that seems to summon from an invalid fish type value) as a result.

Even more peculiar, from spamming the tropical fish spawn egg in creative I've found a tropical fish variant that looks exactly like a Yellowtail Parrotfish, however the bucket name is "Sky-Yellow Dasher" rather than Yellowtail Parrotfish.

Of course, this isn't really a high priority bug issue since it's an issue with a single variant of tropical fish, but from Google searching I've seen a few reports on Reddit and this website of people asking why no one can seem to find a Yellowtail Parrotfish, so I figured that I would report my findings on this issue to possibly get it resolved.

Steps to Reproduce:

1. Enable cheats to activate commands

2. Type the command;  "/summon tropicalfish ~ ~ ~ minecraft:become_yellow_tail_parrot"

Expected Results:

(Successfully summons a Yellowtail Parrotfish)

Observed Results:

(Summons a white kob instead)

Edit: Here's a recording of this bug in action;

https://youtu.be/IvC_7UYuLEM