Fish Lice: Branchiura

Only the behavior of Argulus is well known. They use their mandibles to scrape skin into their mouth. They use their needle-like mouthparts to inject chemicals into the host's body. These chemicals may help turn nearby tissues into liquid so that they can be sucked into the mouth.

After taking a meal, mature females leave their hosts to lay eggs. They glue their eggs in rows on hard surfaces and leave them to hatch on their own. The newly hatched larvae (LAR-vee) do not resemble the adults at all. Their antennae, mouthparts, and first two pairs of thoracic limbs are bristly and used for swimming. They grow by molting, or shedding their external skeletons (exoskeletons). After the second molt, fish lice replace the bristles on the antennae with strong claws in preparation for their new lives as parasites. The claws are used to grab on to their first host. As they grow and develop, fish lice will change hosts several times. As the larvae mature, they develop thoracic limbs, sucking mouthparts, and reproductive organs.

Both males and females are required for reproduction. In most species, males transfer their sperm directly to the reproductive organs of the female with their third and fourth pairs of thoracic limbs. In Dolops, however, males transfer their sperm inside a packet.