Anorexia Reduces the Severity of Cryptobiosis in Oncorhynchus mykiss

Abstract

Cryptobia salmositica multiplied more rapidly and caused a more severe disease with a higher mortality (65%) in rainbow trout (Oncorhynchus mykiss) fed a 52% protein diet than in fish fed 37 or 22% protein diets (25 and 30% mortalities, respectively). Also, plasma protein was significantly higher in fish fed a 52% protein diet than in fish fed 37 or 22% protein diets. Anorexia in infected trout was related positively to parasitemia and was most significant at 4 wk postinfection. During the chronic phase of the infection, food consumption increased with declining parasitemia. It is hypothesized that anorexia lowers plasma protein level, which reduces the multiplication rate of parasites, thus decreasing the severity of the disease.

Effect of Cryptobia salmositica-induced anorexia on feeding behavior and immune response in juvenile rainbow trout Oncorhynchus mykiss

“…Additionally, 2 fish died from cryptobiosis at this time and temperature. These results confirm earlier studies on the relationship between increasing parasitemia and the onset of anemia and anorexia (Li & Woo 1991, Thomas & Woo 1992. Lysis of erythrocytes occurs through (1) a metalloprotease secreated by the parasite (Zuo & Woo 1997, and/or (2) the formation of immune complexes on erythrocytes activating complement-mediated hemolysis (Thomas & Woo 1988.…”

“…reduction in food consumption (Symons 1985), is a characteristic response of fishes to viral (Damsgard et al 1998), bacterial (Neji & de la Noue 1988, Pirhonen et al 2000 and parasitic (Thomas & Woo 1992, Dezfuli et al 2003 diseases. It occurs in cryptobiosis, and its onset has been associated with the acute phase of the disease, which is characterized by high parasitemia and severe anemia in rainbow trout (Li & Woo 1991, Thomas & Woo 1992. Conversely, a return of appetite has been associated with the establishment of an immune response against the pathogen that significantly reduces the parasitemia and anemia.…”

“…Conversely, a return of appetite has been associated with the establishment of an immune response against the pathogen that significantly reduces the parasitemia and anemia. Li & Woo (1991) showed anorexia to be beneficial, as it lowers plasma protein, thus reducing parasitemia and, consequently, the severity of the disease (Woo 1979).…”

Purified metallo-protease from the pathogenic haemoflagellate Cryptobia salmositica and its in vitro proteolytic activities

“…However, the mechanism for the direct transmission is unknown. Infected rainbow trout Oncorhynchus mykiss develop anaemia, exophthalmia, splenomegaly, abdominal distension with ascites, general oedema (Woo 1979) and anorexia (Li & Woo 1991. Cryptobiosis may result in high mortality in naturally and experimentally infected fish, but the mechanism of the disease is not well understood (Woo 1987(Woo , 1994.…”

Contribution of food deprivation to the immune response in rainbow trout ( Oncorhynchus mykiss ) vaccinated against Cryptobia salmositica and Aeromonas salmonicida

“…The higher parasitaemia was because the fish in Group III were fed to satiety and consequently had higher nutrients in their blood to support more rapid multiplication of the parasite. On the other hand, anorexia reduces the severity of the disease because it lowers the amount of serum proteins and hence the parasitaemia (Li and Woo, 1991). This study shows that deficient diets may be beneficial in some parasitic diseases by modulating parasitaemia in the host.…”