The effect of yeast supplementation on the growth and immune system in rainbow trout (Oncorhynchus mykiss)

BACKGROUND: Today, uses of natural substances are preferred to chemical and synthetic compounds for growth and immune enhancement of aquatic organisms. OBJECTIVES: The aim of this research was to evaluate the effect of Saccharomyces cerevisiae extract and hydrolyzed powder on growth parameters and resistance of rainbow trout against temperature and hypoxia stresses with a bacterial challenge. METHODS: For this purpose six hundred rainbow trout (50 ± 5 g mean weight) were purchased from a local fish farm and transferred to the laboratory. After acclimatization to the laboratory conditions the fish were randomly divided into four groups each with triplicate. The first group was fed with a commercial diet (control) while the other groups received yeast extract, hydrolyzed powder and a mixture of them with the commercial diet. Fish were cultured in a 300 l polyethylene tank for 60 days and growth parameters were analyzed at days 0 and 60. Also, at the end of study the fish were challenged with hypoxia and temperature stresses with an experimental bacterial infection. RESULTS: Results showed that the extract and hydrolyzed powder of Saccharomyces cerevisiae in combination significantly (p=0.021) improved rainbow trout growth parameters compared with the control. The results also proved that fish survival significantly increased following feeding with a mixture of the extract and hydrolyzed powder after thermal (69.55±4.59), hypoxia (96.55±5.34) and yersiniosis (49.11± 2.18) challenge than the control. CONCLUSIONS: Dietary administration of yeast extract with mixture of hydrolyzed powder of Saccharomyces cerevisiae could improve rainbow trout growth parameters and increase the resistance against stresses and disease.