Home : Features : Fish and Wildlife Health : Program Projects and Research

Shrimp Disease

Concerned citizens report diseased pink shrimp from the northern Indian River Lagoon.

---

Since early February 2005, we have had a number of reports from concerned citizens in the northern Indian River Lagoon (IRL) regarding diseased pink shrimp that have been found in the Titusville and Melbourne area and in the Mosquito Lagoon. Shrimp have been reported to have a purplish-mauve coloration on the cuticle and to have large white “tumors” or “cysts” in the muscle. Observations from the public have suggested that there is a marked increase in the prevalence of the disease compared to previous years (1-5%), with anywhere from a 5 to a 20% prevalence this year. This has not been investigated or confirmed by independent sampling. That we have received notification about the disease from several different sources and from people very familiar with shrimping in this area suggests that something unusual might be happening.

 

Through the assistance of the public, we have been sent multiple  specimens of diseased pink shrimp (Farfantepenaeus duorarum) from the IRL to examine.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Based on our analysis of this sample, we have determined that the shrimp have a disease known as “cotton” or “milk” shrimp caused by a parasite infection of primarily the abdominal muscle. The muscle has a “cottony” appearance, which is externally visible as white opaque patchy areas under the carapace.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The disease is caused by a severe infection of parasitic microsporidia. Although there are several species of microsporidia known to infect shrimp, we have tentatively diagnosed this species as Agmasoma (= Thelohania) duorara based on spore morphology and host species. The white mass is not a cancerous tumor or cyst but is caused by hundreds of microscopic parasites. The presence of the parasite can elicit a host response by the shrimp that leads to a buildup of blue-black pigmentation in the cuticle. Pigmented cells (melanophores) normally present in the shrimp’s cuticle respond to the parasite’s presence by expanding and causing an increased darkened discoloration of the carapace.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The parasite principally infects and replaces the muscle of the shrimp but can be found in other organs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The white mass in the muscle of the shrimp

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

is composed of thousands of microscopic parasite stages

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

known as sporonts, each containing eight spores.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This parasite species is commonly found in pink shrimp. We are more familiar with microsporidian infections in fish, but microsporidia can infect animals in a wide range of phyla, including insects.

 

The life cycle of this parasite is indirect and thought to involve another host, possibly fish. When a pink shrimp feeds on spores from another source, the internal filament (like a cnidocyst) in the spore releases and allows a sporoplasm (like a tiny amoeba) inside the spore to exit. The sporoplasm is thought to invade the host blood cells (hemocytes) in connective tissue surrounding the intestine. The microsporidian divides in the hemocytes until they reach the skeletal muscle tissue, where they divide further and form more spores. There are usually eight spores per sporont. The infections result in massive invasion of the muscle tissue resulting in some destruction (lysis and necrosis) and replacement of the tissue by the parasite.

 

Infected shrimp can become weakened or paralyzed, and behavioral changes are likely to ensue. This in turn may increase the shrimp’s risk of predation and susceptibility to handling and other diseases; the infection may also result in reduced fecundity. It is important to remind shrimpers that it is not a safe practice to toss dead shrimp back in the water, because this can just perpetuate the parasite’s life cycle. Diseased shrimp should be buried or otherwise disposed of away from the water.

 
We do not know what the extent of this disease is in the IRL shrimp population nor why it seems to be increasing, but we intend to do assessments of shrimp health in the IRL to try to understand both aspects of the disease. Agmasoma duorara has previously been described in pink shrimp in Florida (Iversen and Manning, 1959). The parasite is also a known pathogen in aquaculture, where several shrimp species can be affected and the product is unmarketable. Agmasoma duorara is not a risk to human consumers. However, if the shrimp appear to be obviously weakened or debilitated by the infection, then it may be advisable to refrain from eating such specimens.

 

 

Report prepared by:

 

Jan Landsberg Ph.D.  and  Yasu Kiryu Ph.D.

Fish and Wildlife Health

Fish and Wildlife Research Institute

Florida Fish and Wildlife Conservation Commission

100 Eighth Avenue SE

St. Petersburg, FL 33701-5095

Tel # 727-896-8626

Fax# 727-823-0166