Squalius alburnoides and Squalius pyrenaicus inside an artificial pond where researchers studied them. Miguel Morgado-Santos A female and male get together. One thing leads to another, and they have sex. His sperm fuses with her egg, half of his DNA combining with half of her DNA to form an embryo. As humans, this is how we tend to think of reproduction. But there are many other bizarre ways reproduction can take place. For instance, scientists have discovered a fish carrying genes only from its father in the nucleus of its cells. Found in a type of fish called Squalius alburnoides, which normally inhabits rivers in Portugal or Spain, this is the first documented instance in vertebrates of a father producing a near clone of itself through sexual reproduction — a rare phenomenon called androgenesis — the researchers reported in the journal Royal Society Open Science on Wednesday. The possibility of androgenesis is just one of many mysteries about Squalius alburnoides. It’s not a species in the usual sense, but rather something called a hybrid complex, a group of organisms with multiple parental combinations that can mate with one another. The group is thought to have arisen from hybridization between females of one species, Squalius pyrenaicus, and males of another species, now extinct, that belonged to a group of fish called Anaecypris. To sustain its population, Squalius alburnoides mates with several other closely related species belonging to the Squalius lineage.