There are many parasites which cause skin and gill damage in fish. Neobenedinia is one such parasite found in saltwater fish. A capsalid, it is much larger than other fish parasites and can therefore inflict more damage.
The parasites damage the skin -- the protective barrier against water-borne organisms -- and gills, causing sores, ulcers and small bleeding spots all over the fish's body. Due to the damage to the gills, the infected fish have difficulty breathing. Skin damage will also leave fish more susceptible to secondary infections.
Unless the infection is treated in early, the parasites cause death in the fish.
The parasites lay sticky eggs, which adhere to the nets and other objects put in the water. The parasite then roam the water in search of their hosts: fish.