Margaritifera laevis

From Fish
Numerous glochidia parasitized the gill..
Heavily infected gill with M. laevis.
Glochidium larvae of M. laevis

Margaritifera laevis (Glochidium) are a freshwater pearl mussel (Taxonomy: Mollusca, Bivalvia, Unionoida). These parasites infect the gills of Salmonid fish

Life cycle

Freshwater bivalves of the superfamily Unionoidea contain a parasitic stage in the reproductive cycle that typically includes a fish host and a modified larva, the glochidium. The glochidia develop from fertilized eggs that are maintained in the gills of the female or the hermaphrodite parents and are released into the water where they must attach to the gills or fins of, in some cases, specific fishes to develop a parasitic stage[1].

The adult shell of Margaritifera laevis, a freshwater bivalve, is about 10 cm long, ellipsoid and thick. Its valves are white internally, while blistered externally. The mussels habit in sand, gravel and small stones in fast-flowing rivers and streams. The glochidia are released in summer, and attach to the fish’s gill. They remain for several months, transferred to the upstream by the host’s migration, until they drop off and live partly buried in the sand.

Clinical signs

Infected fish usually exhibits no external abnormality. A number of parasites (0.07-0.46 mm) are observed in the gill.

Generally, its pathogenicity is low. However, heavily infected fish (thousands of parasites per one fish) dies due to the impairment of gas exchange [2].

Since this parasite is not infectious to human, it is harmless in food hygiene.

Diagnosis

The parasite can be morphologically identified by the stereomicroscopic observation.

Treatment

It is recommended not to use the river water in order to prevent the invasion of the parasite. For example, rear the fish by filtered water.

References

  1. Araujo, R. & Ramos, M. A. 1996 The last living population of Margaritifera auricularia (Spengler 1793). In Abstracts of the molluscan conservation conference (ed. M. B. Seddon & I. J. Killeen), pp. 1^2. Cardiff: National Museum and Gallery.
  2. Awakura, T. (2006) Glochidium infection. New atlas of fish diseases (Hatai K. and K. Ogawa), Midori Shobo, p. 48