Evaluation of the Ability of Partially Autolyzed Yeast and Grobiotic‐A to Improve Disease Resistance in Rainbow Trout

Abstract

AbstractWe evaluated the ability of partially autolyzed yeast and Grobiotic‐A to improve immune response and disease resistance in rainbow trout Oncorhynchus mykiss. Experimental diets were prepared by adding partially autolyzed yeast or Grobiotic‐A to a practical trout diet at the manufacturer‐recommended level of 2%; the control was the same diet without supplementation. Rainbow trout (initial weight = approximately 14.3 g) were cultured in 145‐L fiberglass tanks (50 fish/tank; 3 tanks/diet) in a freshwater flow‐through system. Fish were hand‐fed the diets to apparent satiation 3 times/d, 6 d/week for 9 weeks. At 3 and 9 weeks postweighing, fish were sampled to determine respiratory burst activity, plasma protein, total immunoglobulin and lysozyme, and tumor necrosis factor‐alpha (TNF‐α) expression. At the conclusion of the feeding trial (9 weeks), fish remaining after sampling were pooled by diet; one subsample was examined for the ability to respond humorally to infectious hematopoietic necrosis virus (IHNV), and another subsample was challenged by intraperitoneal injection with IHNV. Dietary inclusion of 2% partially autolyzed yeast or Grobiotic‐A had no negative impacts on health or growth of rainbow trout. In contrast, although substantial variability was observed for immune response variables, use of 2% partially autolyzed yeast or Grobiotic‐A produced striking improvements in survival of rainbow trout after experimental challenge with IHNV.