General Discussion

It's a fancy goldfish, most likely a Ranchu (or possibly an Oranda).

@volcaholic1

From the X post video, it's a classic fancy goldfish with a large, bumpy "wen" (the fleshy head growth), rounded body, and prominent eyes. It's actively eating long strands of green filamentous algae (string algae), which explains the humorous "natural maintenance" caption for a giant green pool.

@volcaholic1

Key identifying features:Wen (head growth): The textured, cauliflower-like lump on top of the head is a hallmark of Ranchu and Oranda varieties.
Body shape: Short, egg-shaped body typical of fancy goldfish (selectively bred from common goldfish).
Color: Pale orange/peach with some yellow tones.
Behavior: Enthusiastically munching algae, which these fish do well in ponds or large setups.

Ranchu goldfish are a Japanese breed often called "lionheads" due to their wen; Orandas are similar but usually have a dorsal fin (this one appears finless on top, pointing more to Ranchu). Fancy goldfish like these are popular in ponds and can help control algae, though they're best in well-maintained water (not heavily treated pools).

youtube.com

One reply in the thread even calls it a "ranchu goldfish" directly.

@volcaholic1

These are hardy but sensitive to poor water quality—perfect for a joke about cleaning up green water! If you have more details or another angle, I can refine this.