Gregarine Disease of Penaeid Shrimp

Category

Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Gregarine disease of penaeid shrimp, Gregarine infection, Gregarine parasitism.

Scientific name or taxonomic affiliation

  1. Nematopsis spp.
  2. Paraophioidina scolecoides (Eugregarinorida: Lecudinidae).
  3. Cephalolobus penaeus (Eugregarinida: Cephaloidophoridae).
  4. Cephalolobus petiti (Eugregarinida: Cephaloidophoridae).
  5. Cephaloidophoridae setnai (Eugregarinida: Cephaloidophoridae) but validity of genus name is in question.

Geographic distribution

  1. Global but disease reported from cultured shrimp in Ecuador.
  2. Commercial "seed-production" facility in Texas, USA.
  3. Florida, USA.
  4. Mediterranean coast of France.
  5. Bombay, India.

Host species

All penaeids are potential hosts.

  1. Penaeus vannamei and numerous other species of shrimp (including Penaeus duorarum) in which pathology has not been reported.
  2. Penaeus vannamei.
  3. Penaeus aztecus and P. duorarum.
  4. Solenocera membranacea.
  5. Penaeus semisulcatus.

Impact on the host

Trophozoites and gametocytes occur in the lumen and are often attached to the lining of the intestine. In most cases, the reduced absorption of food from the gut lumen or occasional intestinal blockage by the gregarines is thought to be of little pathological importance for the host. However, an inverse relationship was measured between the severity of Nematopsis sp. infection and cultured P. vannamei survival in Ecuador. Infections of Paraophioidina scolecoides were lost from P. vannamei when the shrimp were transferred to an aquaria and the gregarine disintegrated in seawater suggesting that P. vannamei was an accidental host (although other hosts were not identified). In Florida, P. durorarum was experimentally infected with Nematopsis duorari when they ingested mucus strings cast off by molluscs infected with spores.

Diagnostic techniques

Gross Observations: Severely infected shrimp may show a yellowish discolouration of the midgut as seen through the cuticle of the abdomen.

Wet mount: Parasites can be counted (100 × magnification) in an aqueous preparation of intestinal contents scraped from the intestine segment obtained from the posterior portion of the hepatopancrease of a shrimp that had been separated at the abdominal-cephalothorax junction. Any parasites that remain attached to the intestinal wall can be observed in a wet mount preparation of the scraped intestinal segment.

Histology: The parasite occurs in the midgut and often in the lumen of the anterior midgut caecum, the primary ducts of the hepatopancrease, the posterior stomach and in the anterior portion of the hindgut. Significant lesions typically occur in heavy infections and consist of a reduction in the height of the midgut mucosa, hyperplasia of the midgut epithelium to form villus-like folds, and perforations of the midgut mucosa.

Methods of control

For Nematopsis sp., the source of the shrimp seed may be an important factor because wild post larvae had higher survival and lower prevalence of infection then laboratory reared post larvae. Medicated feeds that were tested did not alleviate the infection or improve survival. The source of P. scolecoides was not identified but the shrimp acquired the infection at the culture facility. Because gregarines require at least two hosts (usually a mollusc or annelid worm in addition to the crustacean) to complete their life cycle, infection can be circumvented by removal of the alternate host(s) from the culture facility or water source.

References

Johnson, S.K. 1989. Handbook of Shrimp Diseases. Texas A&M Sea Grant College Program, Galveston.

Jones, T.C., R.M. Overstreet, J.M. Lotz and P.F. Frelier. 1994. Paraophioidina scolecoides n. sp., a new aseptate gregarine from cultured Pacific white shrimp Penaeus vannamei. Diseases of Aquatic Organisms 19: 67-75.

Lightner, D.V. (ed.). 1996. A Handbook of Shrimp Pathology and Diagnostic Procedures for Disease of Cultured Penaeid Shrimp. World Aquaculture Society, Baton Rouge.

Miller, D.J., F. Criollo and O. Mora. 1994. A practical diagnostic method for determining intestinal gregarine infection in Penaeus vannamei on a commercial shrimp farm. World Aquaculture 25: 65-66.

Citation Information

Bower, S.M. (1996): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Gregarine Disease of Penaeid Shrimp.

Date last revised: September 1996
Comments to Susan Bower

Date modified: