Question

How can we say that fish exhibits external fertilisation?

Answer 1

Female fish lay eggs in water while male fish release their sperm in water. Sperm swim and reach the eggs of fish, randomly due to water currents. When a sperm comes in contact with the viable egg, nuclei of both cells fuse to form a zygote. This process of fertilisation takes place in water outside the female body, hence fertilisation is external in fishes.