Swordfish in Steal an Egg

Swordfish (Epic rarity) belongs to the Abyss Ocean zone. Abyss Ocean is zone 7 of 12 on the wiki's Biomes list; the wiki lists its entry requirement as 2.5M speed, and the nests there are watched by the Moby. You get it by carrying the Swordfish Egg back to your pen.

At $1.1K/s base income, Swordfish sits 7th out of 8 in its zone — El Maja tops the Abyss Ocean at $130M/s. The listed figure assumes no mutation and a normal weight.

With a colour mutation and no size bonus, the same Swordfish would earn roughly: Silver ×1.2 ≈ $1.32K/s, Golden ×2.5 ≈ $2.75K/s, Rainbow ×3.5 ≈ $3.85K/s (multipliers from the wiki's Mutations page; arithmetic is ours). Add a Giant (×3) or Huge (×5) size roll on top and the numbers multiply again.

Hatching it pays a one-off reward of +81k Speed, $110k, and the egg takes 2m to grow in the pen. That reward is the reason low-income eggs are still worth stealing early: the speed bonus is what gets you into the next zone.

Epics are the mid-tier of their zone — a good candidate for your first mutation roll because the base rate is high enough to matter.