Task: Question Generation
Input (English): Background Paragraph: Fish reproduce sexually. They lay eggs that can be fertilized either inside or outside of the body. In most fish, the eggs develop outside of the mother's body. In the majority of these species, fertilization also takes place outside the mother's body. The male and female fish release their gametes into the surrounding water, where fertilization occurs. Female fish release very high numbers of eggs to increase the chances of fertilization. 
Story: Two different rivers were stocked with adult fish. Red river had a lower fish population because the fish had hardly reproduced naturally. Black river had doubled it's fish population in two years because they reproduced naturally.
Output (English): Which of the two rivers had fewer fish reproduce sexually?