Microsporeans - Crustacean Diseases Caused By Parasites

Microsporeans

These are intracellular parasites with unicellular spores (3-10 µm) containing sporoplasm and coiled polar filament (Fig. 5-20a).

CAUSATIVE AGENTS:

Nosema  (Ameson), Agmasoma (Thelohania), Pleistophora, Glugea, Ichthyosporidium

SPECIES AFFECTED:

Penaeid shrimps

GROSS SIGNS:

Affected hosts are weakened and easily stressed. Infected areas (cephal-othorax, abdominal muscle, ovary) turn opaque white because of the pres-ence of spores and other stages of the parasite, thus the term “cotton” or “milk” shrimp or “white ovary” disease (Fig. 5-20b, 5-20c). Infection may result in sterility of spawners with white ovaries.

EFFECT ON HOST:

Penaeids with spores in the ovaries become sterile. In crabs, microspori-dians cause lysis of muscle tissues and increase vulnerability to stress.

DIAGNOSIS:

Microscopic examination of fresh squashes of Giemsa-stained smears from infected areas will reveal spores. Histological sections also provide positive identification.

PREVENTION AND CONTROL:

•               Isolate and destroy infected individuals

•               Avoid contact of infected broodstock with offspring

•               Disinfect culture systems with chlorine or iodine