Fish
For the most part, fish are either male or female. All fish reproduce sexually. A fish can have either testes or ovaries. Some fish are hermaphrodites, having testes and ovaries either simultaneously or at different phases in their life. With species of fish that live in groups, or schools, eggs and sperm are released at the same time. Then the sperm would have to swim and find an egg to fertilize. Since the eggs develop outside of the female fish, these fish are oviparous. However, there are some oviparous fish that practice internal fertilization. In this case, the male would have to use an intermittent organ to deliver sperm into the female's genital opening. The males would also need a pair of fins known as claspers to grab hold of the female in order to mate.