Comparison of Dried Yeasts, Candida Utilis and Saccharomyces Cerevisiae, as Supplements in a Diet for Rainbow Trout

Abstract

A single grade of the yeast Saccharomyces cerevisiae and three grades of the yeast Candida utilis were tested as growth stimulants and as vitamin sources when fed in a dry pelleted diet to rainbow trout. At levels of 4 percent, 8 percent and 15 percent of dry yeast in the diet, growth was stimulated and conversion ratios improved. Maximum growth occurred on 8-percent yeast diets. With the exception of one grade of C. utilis, all yeasts at the same levels in the diet gave similar results. Vitamin analyses indicated that diets enriched with 4-percent of yeast were deficient in meeting the daily requirement levels of B-vitamins. Because no appreciable mortality occurred after feeding these diets for 18 weeks, it is suggested that reported daily requirements are high. Storage of diets at room temperature for 180 days had little destructive effect on B-vitamin content, except some loss in niacin occurred. A commercial pelleting process effected no loss in B-vitamin content. The mortalities of trout on yeast-fortified diets and the yeast-free diet were similar. Liver necrosis in trout on the diets for 33 weeks appeared to a like degree for all diets tested. At similar levels in the diet, C. utilis yeasts promoted higher storage levels of biotin. Trout on 8-percent yeast diets had less liver biotin than those on 4-percent yeast, 15-percent yeast and yeast-free diets. When trout are fed a pelleted diet at 60 percent of that recommended in Cortland Feeding Chart, they attained a coefficient of condition, empirically expressed as “R”, of 1.80 to 1.86 on the yeast supplemented diets and of 1.73 on the yeast-free diet.