When to Outcross
Fry showing deformities (spine curves, missing fins, small size) = inbreeding depression.
Reduced fertility (smaller broods, weak fry).
Color loss despite careful selection.
Any of these means it is time to introduce new genes.
Choosing the Right Outcross
Same color class and tail type as your strain. A Red Delta pairs with another Red Delta, not with a Moscow Blue.
From a reputable breeder with documented lineage — random pet store guppies destroy years of work.
The Cross
Pair outcross male to best females of your line. Raise offspring fully.
Expect first-generation mix. Cull aggressively for the traits closest to your original strain.
Back to Line Breeding
After 1-2 outcross generations, return to line breeding using the best outcross-influenced fish.
Strain quality usually jumps within 2 generations of the refresh.