Stickleback Parasites

(version 1.0;   01/27/04)


Unlike most model organisms used to study genetics and molecular biology, sticklebacks are caught in the wild where they are subject to infection by parasites and diseases.  Often they come back to the lab with the fish.  Some of these can cause problems with survival and fertility in captivity and a few are contaigous and can spread from tank to tank.  Listed below are a few we have encountered in our own collections.  During the husbandry discussion in the course, we will compare experiences with these and other parasites in different labs and how best to avoid or cope with them.


Schistocephalus (Schistocephalus solidus)[1]  is a tapeworm dependent on two intermediate hosts and a definitive host to complete its life cycle. The tapeworm life stage found in fish is a larval or plerocercoid stage. Often several larval tapeworms may be found in a single fish and can comprise a large portion of the total volume or weight of the host. Fish infested by tapeworms often exhibit impaired movement and can be identified by a swollen abdomen. When piscivorous birds such as mergansers, blue heron, or other fish eating birds consume the fish, the larval tapeworm attains sexual maturity within a few days, produces eggs for several days, and then dies. Eggs are then expelled from the bird in fecal matter. Eggs that reach the water are taken up by small crustaceans (copepods), where the first larval or procercoid stage develops. The copepods are in turn eaten by fish to complete the life cycle.  Because of the complex life cycle, this common parasite is not contaigous in the laboratory and we have never seen it in lab-reared fish.  However, we have found that infested females do not produce eggs reliably and it is important to make sure that you bring back healthy fish from the field if you intend to breed them.  Occasionally, we have successfully de-wormed fish by squeezing out the parasite. 


Glugea (Glugea anomala)[2]  is a microsporidian.  These organisms are intracellular parasites with a direct life cycle.  When the thick-walled spore is injested by the host, the sporoplasm is discharged from within the spore where it migrates to the target organ and begins to proliferate.  The proliferating Glugea accumulate in cysts, or xenomas. In sticklebacks, the xenomas can occur in virtually any tissue and are often visible as white cysts bulging from the skin surface.  Glugea is highly contaigous because mature spores are released into the water from lesions on the body surface.  If the infection gets bad enough, it can be fatal to the fish.  There are no proven remedies for microsporidian infections and disinfection and quarantine are the only known methods to prevent spreading the disease.  


[1] From the Oregon Department of Fish and Wildlife.

[2] This information is from a fish pathology book owned by the Stanford veterinary service.