Catfish in Steal an Egg

Catfish hatches from the Catfish Egg, an Uncommon-rarity egg found in the Lake. Lake is zone 2 of 12 on the wiki's Biomes list; the wiki lists its entry requirement as 900 speed, and the nests there are watched by the Swan.

The wiki lists its base income as $12/s, which ranks it 6th of the 8 Lake pets by base rate — Leviathan tops the Lake at $220K/s. Base rate is what a normal-size, un-mutated hatch earns; everything above that comes from the size roll and the colour mutation.

With a colour mutation and no size bonus, the same Catfish would earn roughly: Silver ×1.2 ≈ $14/s, Golden ×2.5 ≈ $30/s, Rainbow ×3.5 ≈ $42/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 +2.5k Speed, $1.2k, and the egg takes 30s 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.

Uncommons are cheap speed: hatch them for the reward, then move on.