Enhancement of vibriosis resistance in juvenile Penaeus vannamei by supplementation of diets with different yeast products

Penaeus vannamei were reared on five different experimental diets containin g: (1) Saccharomyces cerevisiae at 1%; (2) beta-glucan, extracted from S. c erevisiae, at 0.1%; (3) Phaffia rhodozyma at 1%; (4) experimental yeast (HP PR1) at 1% and; (5) a control diet. Wet weight, survival (5) and feed conve rsion ratio were monitored over a 7-week period. Results indicate that, whi le there was no significant difference in weight gain on the different diet s (P = 0.196), survival of animals reared on the diets containing S. cerevi siae, P, rhodozyma and the experimental yeast was significantly higher (P = 0.006) than the animals reared on the diet containing beta-glucan, and hig her, though not significantly, than those reared on the control diet. Bioma ss was found to be statistically different (P = 0.042), the animals reared on the P. rhodozyma diet displaying greater biomass than the animals on the beta-glucan diet. Feed conversion ratio was not different for any of the d iets (P = 0.233). At the end of the growth trial, the ability of the shrimp to clear bacteria from the hemolymph was tested by immersing the animals i n a viable cell suspension of Vibrio harveyi strain BP05. Twenty-seven hour s post immersion, the animals fed the S. cerevisiae, P. rhodozyma HPPR1 and control diet had effectively cleared the bacteria from the hemolymph and w ere not statistically different from nonchallenged control shrimp, while th e animals fed the glucan diet still displayed elevated numbers in the order of 10(3) CFU/ml (P = 0.002). Additionally, mortalities were noted for thes e animals during the immersion challenge, unlike for the animals on the oth er treatments. Determination of phenoloxidase activity of the animals showe d a significant difference among the five treatments with phenoloxidase act ivity for the Phaffia-treated animals being significantly lower (P = 0.003) than any of the other diets except the beta-glucan diet. These results ind icate that even though no clear immunostimulatory effect could be found for the different treatments, it appears that all three yeasts, and especially the Phaffia diet, had a positive effect on the animals, leading to better survival. The animals on the glucan diet showed poor performance overall, i ndicating that not only did this treatment not aid in increasing resistance of the animals to infection, but on the contrary, these animals showed red uced performance when compared to the animals fed the control diet. (C) 199 9 Elsevier Science B.V. All rights reserved.