At 10degreesC, 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 x 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 x 10(5) parasites ml(-1)) and were anemic (pack cell volume, PCV, of 24.4%). However at 5degreesC, anorexia occurred at 5 w.p.i. (0.81% b.w.), and was most severe at 7 w.p.i. (0.40% b.w.). At 8 w.p.i. (0.43% b.w.), fish displayed high parasitemia (4.6 x 10(6) parasites ml(-1)) and low PCV (10.8%). Fish at 5degreesC had lower gastric evacuation (GE) rates (GE(48h)) than 10degreesC fish, however there were no differences between infected and naive 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 5degreesC respectively). Significant correlations were detected between b.w. and MSM before onset of anorexia at 10degreesC (p = 0.005) and 5degreesC (p = 0.02); this was maintained at 10degreesC (p = 0.001) but not at 5degreesC (p = 0.98). Fish on an anorexic diet (0.93% b.w.) responded well at 10degreesC to a live C. salmositica vaccine; this could partly be due to constant antigenic stimulation by the live vaccine.
