Female Acheilognathus lanceolatus and male Acheilognathus limbatus from Japan can produce fertile hybrid offspring. These hybrids can interbreed and give birth to viable offspring. The F2 generation of these hybrids is also fertile and can produce more offspring. Even though these two fish species live in the same area in Japan, natural hybrids have not been seen yet. The researchers discuss factors that could either help or prevent these species from interbreeding in the wild.