Several freshwater fish species have been experimentally infected with a parasite that normally only infects marine fishes.
Enteromyxum leei, a myxosporean parasite, infects a wide range of marine fishes and new evidence has shown it is capable of infecting freshwater fish, too.
Diamant, Ram and Paperna of the National Center for Mariculture in Israel experimentally infected 17 species of freshwater fish with Enteromyxum leei and found that four species were highly susceptible.
Their paper in Diseases of Aquatic Organisms said that Tiger barbs, Puntius tetrazona, Zebra danios, Danio rerio, Oscars, Astronotus ocellatus and Mozambique tilapia, Oreochromis mossambicus, were found to be susceptible with prevalences ranging from 53 to 90%.
"The course of infection and pathology was limited to the gut mucosa epithelium and was similar to that observed in marine hosts," the authors wrote.
"Little is known of the differences in physiological conditions encountered by a parasite in the alimentary tract of freshwater vs. marine teleost hosts, but we assume that a similar osmotic environment is maintained in both.
"Parasite infectivity may be influenced by differences in the presence or absence of a true stomach, acidic gastric pH and digestive enzyme activity both in the stomach and intestine. Variability in susceptibility among species may also stem from differences in innate immunity."
For more details see the paper: Diamant A, Ram S, Paperna I (2006) - Experimental transmission of Enteromyxum leei to freshwater fish. Dis Aquat Organ. 2006 Oct 17;72(2):171-8.