Effect of high dietary concentrations of brewer's dried yeast on growth performance and liver uricase in rainbow trout (Oncorhynchus mykiss)

The potential of using yeast nitrogen in fish feeds to replace proteins from conventional sources is an attractive option to nutritionists, feed manufacturers and fish farmers. Experiments were conducted to determine the effects of high dietary levels of brewer's dried yeast, with 20% of its protein represented by nucleic acid nitrogen, on the growth, feed conversion efficiency and uric acid metabolism of rainbow trout (Oncorhynchus mykiss).

Growth and liver uricase activities were monitored in trout fed diets containing 0, 25, 50 or 75% yeast. Growth was faster and feed conversion more efficient in fish fed diets consisting of 25% yeast; the diets containing 50 and 75% yeast were seemingly unpalatable to trout. Liver uricase activity, present in all fish, was directly correlated with the dietary level of nucleic acids. It was concluded that although feed intake was depressed at yeast levels greater than 25%, the fish did not appear to be adversely affected physiologically by high dietary levels of nucleic acid nitrogen.