How fish genetics work in Fish of Ganymede

Two copies of every gene

When two fish breed, each parent passes on one of its two copies of each gene, picked at random. That is why siblings from the same clutch can look very different, and why a plain fish can still carry a rare trait hidden in its second copy.

Dominant and recessive traits

Most visible traits (body plan, fins, tail, lure, eyes, scales, pattern) have a dominance order. If the two copies differ, the more dominant one shows. A recessive trait, such as a rare lure or glass scales, only shows when the more dominant copy does not hide it, often only when both copies carry it.

When two traits are equally dominant they can mix: two colours of the same strength blend into a two-tone fish.

Blended number traits

Size, length, body depth and hue shift are numbers from 0 to 9. A fish shows the average of its two copies, so breeding two large parents tends to give large young, and selecting over generations moves the whole line.

Mutations

Each copy has a small chance to mutate when it is passed on (2% per copy), changing to a new value. Mutations are how genuinely new traits enter a line. Fish caught in the deeper ocean zones are more often mutated, and a rare item, the mutation spark, can add more.

Exact odds before you breed

Before you pair two fish, the game shows the exact probability of every trait in the clutch and of each rarity tier. There is no guessing: you plan crosses like a real breeder, and the server rolls the eggs from a stored seed so results are fair and final.

Species and rarity

Try it

The best way to learn is to breed a clutch: the odds panel shows you exactly what each pairing can produce. Real-world fish genetics (bettas, guppies, koi) follow the same basic rules, which is why many fishkeepers enjoy it.

Questions