EFFECTS OF YEAST CELL WALL IN WHITE SHRIMP Litopenaeus vannamei

The objective of this study was to evaluate the effects of Saccharomyces cerevisiae cell wall and nucleotide source on survival rate and resistance against Vibrio parahemolyticus (Early Mortality Syndrome agent) in juvenile white shrimp (Litopenaeus vannamei).

The shrimps were distributed in a completely randomized design, with 5 treatments: 1- Control; 2- 0.5% of Saccharomyces cerevisiae as a source of nucleotides (YNU - Hilyses®, ICC Brazil); 3 - 1% of YNU; 4 - 0.5% of Saccharomyces cerevisiae cell wall (YCW - ImmunoWall®, ICC Brazil); and 1.0% of YCW, with 8 replicates each. These included 4 replicates for growth performance (28 days) and 4 replicates for immunity (bacteria challenge). Each replicate consisted of 100L fiber tank with stocking density of 360 pieces/m³ at 20 ppt salinity. Shrimps PL 8 were purchase from a commercial hatchery and were acclimated for 5 days, and then allocated to treatment tanks. The growth parameters measured were total feed intake (TFI, g/tank), feed intake (FI, g/ind.), daily feed intake (DFI, g/ind./d), body weight (BW, g/ind.), body weight gain (BWG, g/ind.), average daily gain (ADG, g/ind./d), length (cm), specific growth rate (SGR, %/d), feed conversion ratio (FCR), survival rate (SR, %) at 14 and 28 days. Also the shrimp size was evaluated (large, medium and small) at 28 days. Shrimp was challenged by Vibrio parahaemolyticus immersion or orally at of 1.0-2.9x10¹² CFU/mL under normal and salinity stress condition (35 ppt). The immunological parameters were evaluated weekly and daily for mortality rates. The data were analyzed using the GLM (SAS), and means were compared by Ducan's test (P=0.05).

There is no significant difference (P<0.05) among treatments for growth and performance results, except for FI parameters, were the supplementation of YNU and YCW decrease (P<0.05) the FI compared to control group; and for shrimp size, were all feed additives increased compared to control (Table 1). The additives supplementation also increased (numerically) the survival rates compared to control (Table 1). For V. parahemolyticus challenge via oral, both YNU and YCW decrease the hepatopancreas Vibrio ssp. count (P<0.05). However, for immersion challenge and/or with salinity stress, YNU and YCW improved survival rate and decrease the Vibrio spp. count (P<0.05) (Table 2).

In general, the inclusions of 0.5 to 1% of YNU and YCW were able to improve the shrimp Litopenaeus vannamei disease resistance against virulent bacteria, Vibrio parahemolyticus, mainly under high salinity conditions.