They measured key traits of the fish, such as body condition, colouration and the size of the gonopodium, a modified anal fin ...

Fish anatomy reveals that these unique aquatic creatures reproduce sexually by producing and fertilizing eggs and sperm.

Evolving roughly 27 different times in the long history of fish, bioluminescence—the biological production of light—is one of ...

A parasitic fish called a lamprey sometimes attaches itself near a male shark’s claspers, or reproductive organs. This can make it more difficult for scientists to identify an individual’s sex.