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

Abstract

At 10°C, rainbow trout Oncorhynchus mykiss (n = 13 per group) infected with Cryptobia salmositica Katz, 1951 became anorexic at 3 wk post-infection (w.p.i.), with feed-intake decreasing significantly from 1.33 to 0.94% body weight (b.w.). Anorexia was most severe at 4 w.p.i. (0.80% b.w.), coinciding with peak parasitemia (9.2 × 10 6 parasites ml blood -1) and anemia. At 8 w.p.i., fish had recovered their appetite although they still had contained detectable parasites (6.8 × 10 5 parasites ml ) and low PCV (10.8%). Fish at 5°C had lower gastric evacuation (GE) rates (GE 48h ) than 10°C fish, however there were no differences between infected and naïve fish at both temperatures. Before anorexia, there was no significant correlation between mean share of meal (MSM, a measure of how food was partitioned within a group) and coefficient of variation in feeding but this became significant during anorexia (p = 0.02 and p = 0.0002 at 10 and 5°C respectively). Significant correlations were detected between b.w. and MSM before onset of anorexia at 10°C (p = 0.005) and 5°C (p = 0.02); this was maintained at 10°C (p = 0.001) but not at 5°C (p = 0.98). Fish on an anorexic diet (0.93% b.w.) responded well at 10°C to a live C. salmositica vaccine; this could partly be due to constant antigenic stimulation by the live vaccine.

Hypoxemia-induced leptin secretion: a mechanism for the control of food intake in diseased fish

“…Together, these results suggest that the expression of hepatic leptin in rainbow trout is stimulated by hypoxemic conditions and that the appetite-suppressing effects of C. salmositica infection are at least partly mediated by leptin. The parasitemia and hematocrit changes observed in this study are consistent with the known progression of C. salmositica infection in salmonids (Woo & Wehnert 1986, Beamish et al 1996, Chin et al 2004. The number of blood parasites peaked during acute infection at 3-4 wpi and subsequently declined in correspondence with a large increase in the production of Cryptobia-agglutinating antibodies (Sitja-Bobadilla & Woo 1994, Chin et al 2004.…”

“…Among the different parasites known to affect feeding in fish, the effects of the pathogenic hemoflagellate, Cryptobia salmositica (order Parabodonida, class Kinetoplastea), on food intake in rainbow trout have been well characterized (Woo 2003). While the onset of anorexia in Cryptobia-infected fish coincides with a significant rise in parasitemia and a decrease in hematocrit, the return of appetite is associated with the establishment of an immune response that significantly reduces both the parasitemia and anemia (Li & Woo 1991, Thomas & Woo 1992, Chin et al 2004. During acute infection, Cryptobia-infected fish are also characterized by a reduced aerobic scope (Kumaraguru et al 1995) and an increased susceptibility to hypoxia (Woo & Wehnert 1986).…”

Use of a live vaccine to modulate Cryptobia salmositica infections in Salmo salar

“…This study also confirms earlier reports (e.g. Li & Woo 1995, Aredelli & Woo 2002, Chin et al 2004) that the humoral response to the vaccine is an important component in protection against cryptobiosis. …”

“…Clinical signs of cryptobiosis include exophthalmia, splenomegaly, abdominal distension, ascites fluid, anaemia (Woo 1979), and anorexia (Thomas & Woo 1992, Chin et al 2004. The pathogen has been found in all species of Pacific Oncorhynchus occurring along the west coast of North America, and it is transmitted in streams and rivers by the freshwater leech Piscicola salmositica (Woo 2003).…”

Duress without stress: Cryptobia infection results in HPI axis dysfunction in rainbow trout

“…w4 wpi) is associated with marked decreases in head kidney and spleen il1b mRNA expression (L E MacDonald, S L Alderman, S Kramer, P T K Woo & N J Bernier 2013 unpublished observations). Alternatively, the hypoxaemic conditions triggered by the w50% reduction in haematocrit in C. salmositica-infected rainbow trout (Chin et al 2004) may be responsible for the increase in POA crf gene expression. Previously, we have shown that hypoxia exposure can increase the gene expression of POA crf in rainbow trout .…”