Parasite : fish lice

This is a parasite on fish and has a size between 5 and 10mm (you can spot them with the naked eye). They belong to the group of crustaceans, so they have a armor as well. They feed on fish with a kind of needle that punctures the skin and inject digestion juices into the fish. Then they suck the body fluids out of the fish. Like many parasites, they have a high reproduction pace and the breeding occurs on the fish itself. The female leaves the host and will put the eggs on plants or stones and after 20 and 30 days the little ones become active and will look for a new host to further develop. The adult lice can stay up to 5 days without host.
By the way, they are good swimmers and find if necessary quickly another host.