Reduction of herring meal (to 100 g∙kg−1) in rainbow trout (Oncorhynchus mykiss) diets and its replacement by soybean and corn gluten meals led to reduced feed intake and growth. The diamine putrescine, when included in calf diets, reduced the effects of antinutritional factors in soybean meal; it also enhanced the growth of chicks. Putrescine (1–4 g∙kg−1) added to practical trout diets did not increase feed intake or growth over a 12-wk period. Putrescine concentrations in the trout tissues were not increased by this treatment, nor were the activities of the putrescine and polyamine biosynthetic enzymes ornithine decarboxylase and adenosylmethionine decarboxylase significantly changed. When a higher putrescine concentration (13.3 g∙kg−1) was used, in line with the calf diets, it reduced weight gain, feed intake, and gain/feed ratio. Lack of effect of putrescine at the lower concentrations (where it was effective with chicks) was ascribed to the enzyme diamine oxidase, shown to be active in the pyloric ceca and the anterior intestine of the trout. Passage of food through the gastrointestinal tract of trout is about 10-fold longer than in chicks. This may explain the failure of dietary putrescine to elevate tissue putrescine levels in trout.
Subclinical Listonella anguillarum infection does not impair recovery of swimming performance in rainbow trout Oncorhynchus mykiss