Use of hydrolyzed yeast in paralarva and juvenile diets of kingfish Odontesthes argentinensis
Yeast is a nutritional additive rich in nucleic acids, vitamins and immunostimulating factors, and the possibility of using by-products from other companies makes it a product of relatively low value. The present work initially sought to compile information about the application of yeasts and their derivatives with importance in aquaculture, their mechanisms of action and effects in the most diverse aquaculture species. Although the yeast is used whole, active (as a probiotic) or inactive, the removal of the cell wall seems to be an alternative for increasing the availability of intracellular nutrients. According to the factors that are used to trigger the lysis process, we can differentiate at least two products: autolysed and hydrolyzed yeast.Yeast can also be used as a vehicle for supplementing nutrients of interest, such as selenium, in selenized yeast. Among the main species used, Saccharomyces cerevisiae and Candida utilis are highlighted for being efficient immunostimulants and also an alternative source of proteins. Hydrolyzed yeast was the product chosen for testing larvae and juveniles of Odontesthes argentinensis. In the two experiments performed, two commercial products were used, here called Y1 (consisting of S. cerevisiae and C. utilis) and Y2 (consisting only of S. cerevisiae). Artemia nauplii were enriched with 1g L-1 of each product and offered to the larvae for 20 days (0 - 20 days after hatching).It was found that the larvae that received hydrolyzed yeast had higher growth rates, even after 10 days of supplementation cessation. At the end of the 20 days, with a salt stress test, there was greater resistance in larvae that were fed with Artemia enriched with Y1. Additionally, hydrolyzed yeast had an important immune function, with an increase in the area of lymphoid organs (thymus and kidney) and the lymphocyte population (T and T helper). In a second experiment, juvenile kingfish received a diet supplemented with 0.5% hydrolyzed yeast (Y1 and Y2) for 50 days. The concentration used of the respective products for this period had no influence on growth and immune parameters, nor was it effective in improving intestinal morphology.Yeast and its derivatives have great potential for use in aquaculture, whether due to products already on the market, or for the development of new products. Hydrolyzed yeast was effective in improving growth and immune parameters, in addition to promoting greater resistance to salt stress in kingfish larvae, the same cannot be said for juveniles, where the inclusion of 0.5% yeast hydrolyzed for 50 days did not promote growth or immune response.