Every fish has 24 genes. Each gene has two copies, one from each parent. Most genes pick a trait (a tail shape, a pattern, a body plan); the rest are numbers (sizes) that blend.
Which copy shows
Every trait has a dominance from 0 to 3. When a fish’s two copies differ, the one with higher dominance shows and the other is carried hidden. When both have the same dominance, the fish shows a mix of the two (codominance). Rare traits tend to have low dominance, which is why they hide so easily: a fish needs two copies of a fully recessive trait (dominance 0) for it to show. Each trait’s dominance is listed on the Traits page.
What the young get
For every gene, an egg takes one of the two copies from each parent, at random (50/50). So two parents that both carry a hidden trait have a 1 in 4 chance per egg of a young fish that shows it:
| Parent B passes the shown trait | Parent B passes the hidden trait | |
|---|---|---|
| Parent A passes the shown trait | shows the common trait | carries the rare trait hidden |
| Parent A passes the hidden trait | carries the rare trait hidden | shows the rare trait |
Half the eggs will carry it hidden, which makes them useful parents for the next step.
Size genes
The 10 number genes (body size, body hue shift, body length, body depth, head size, head crest size, lure length, dorsal fin height, tail size, fins size) each hold a value from 0 to 9 per copy. The fish shows the average of its two copies. Young get one copy from each parent, so these blend: breeding the biggest with the biggest, and keeping the biggest young, pushes a line up over generations.
Pure lines
A fish with the same rare (or rarer) trait on both copies is a pure line for it: every one of its young gets a copy. Two fish pure for the same trait always have young that show it. Pure lines are marked on your fish.
Mutations
Each copy has a 2% chance per egg of mutating. A trait mutates into a different one at random (rarer ones less often); a number gene shifts by 1 to 3. Mutations are real genes and are passed on. The mutation spark item, breeder skills and the deeper water raise the rate. Mythic traits never come from mutations.
Seeing hidden copies
- You always see every copy of your own fish.
- Other players see only what shows, with a “?” for copies they can’t see, unless the owner used a gene lens (then everyone sees everything, for good).
- A gene probe from the Gene Lab shows you, privately, the hidden copies of another player’s fish.
The breeding planner ranks every possible mate by the exact chance their eggs show (and carry) the traits you pick, with the Punnett square for each.