Vulgaris Fish-gill Isopod, Elthusa vulgaris

Vulgaris Fish-Gill Isopod, Elthusa vulgaris, Male. Isopod provided by the commercial fishermen of the greater Los Cabos area, November 2011. Size 2.6 cm (1.0 inch). Identification courtesy of Dr. Julianne Passarelli, Cabrillo Marine Aquarium, San Pedro, California.

Vulgaris Fish-Gill Isopod, Elthusa vulgaris, Female. Isopod provided by the commercial fishermen of the greater Los Cabos area, March 2014. Size 3.4 cm (1.3 inches).

Phylogeny: The Vulgaris Fish-gill Isopod, Elthusa vulgaris (Stimpson, 1857), is a common ectoparasite that is a member of the Cymothoidae Family of Fish-gill Isopods. Cymothoidae is a large Family with forty-two genera and there are thirty-four species within the Genus Elthusa. In Mexico this species is known as isópodo branquial de pez.

Morphology:  The Vulgaris Fish-gill Isopod has a symmetrical, ovate, flattened, body with an abdomen that taper smoothly from the thorax. The telson (tail flap) is twice as broad as long. The head is sunken into the first thorax segment. A key to identification is the long legs with pointed tips that they utilize to cling to their host fish. The Vulgaris Fish-gill Isopod is a uniform cream color.  Vulgaris Fish-gill Isopods range in size from from 1.2 cm (0.5 inches) to 4.4 cm (1.75 inches) in length. The males having smaller narrower bodies than females.

Habitat and Range:  Both male and female Vulgaris Fish-gill Isopods are found attached to the gills of fishes; females, on occasion, can also be found within a fish’s mouth. The juveniles attach themselves to any fish they can find and with maturity will change to a specific host and become a permanent resident. Vulgaris Fish-gill Isopods are found from the surface to depths of 3,000 feet, but are not present in fishes from the intertidal zone.  Vulgaris Fish-gill Isopods range from Washington State to Columbia. They are found in all Mexican waters of the Pacific Ocean, including the entire Gulf of California.

Diet:  Vulgaris Fish-gill Isopods are ectoparasites that feed on the blood and tissue of their hosts. This behavior causes tissue damage, blood loss, and secondary bacterial infections in their hosts; this very seldom results in the death of the host. Some sources say that  females consume left over food scraps, but others doubt that their mouth parts would allow such behavior.

Predators:  Infected fish visit cleaning stations to have parasites, such as Vulgaris Fish-gill Isopods, removed. At these stations various species of cleaner shrimp and cleaner wrasse remove and consume these parasites.

Reproduction: The Vulgaris Fish-gill Isopod is a protandrous hermaphrodite containing both sex organs with males transitioning to females at mid-life. Once they become female, they lose their ability to crawl and are committed to their current host. The females are capable of releasing a pheromone that prevents the males in the vicinity form changing to females. Fertilization is internal, with the female carrying the eggs in a marsupium (pouch), until they hatch into their larval form.

Ecosystem Interactions: The behavioral study of the Vulgaris Fish-gill Isopod is difficult as the majority are taken via bottom trawls and the males commonly abandon their hosts before the trawl reaches the surface. Very little is known as to their interaction with other species, other than their host fish.

Human Interactions:  Vulgaris Fish-gill Isopods have no significant impact on human activities. Their affect on fisheries is minimal. The effect of isopods on humans if consumed is unknown. From a conservation perspective they have not been formally evaluated however they have are common with a fairly wide distribution and should be consider to be of Least Concern.

Synonym:  Lironeca vulgaris