Fermentation of Soybean Meal with Lactobacillus acidophilus Allows Greater Inclusion of Vegetable Protein in the Diet and Can Reduce Vibrionacea in the Intestine of the South American Catfish (Rhamdia quelen)

Abstract

The objective of this study was to evaluate the effect of diets containing different inclusion levels (0%, 7%, 14%, 21% and 28%) of soybean meal fermented by Lactobacillus acidophilus (SMFL) on the zootechnical performance and intestinal health of South American catfish juveniles (Rhamdia quelen). The experimental design was completely randomized with five treatments and four replications and lasted 56 days. Five isoproteic (39% crude protein) and isoenergetic (4300 kcal of gross energy kg^-1) diets were formulated where SMFL was included in replacement of fish meal. Two hundred forty South American catfish juveniles (3.0 ± 0.5 g) were distributed in 20 tanks (70 L) connected in a recirculation aquaculture system. At the end of the experiment, the inclusion of SMFL up to 21% in replacement of fish meal did not affect the zootechnical performance and also decreased the concentration of Vibrionaceae bacteria present in the intestine compared to the control group. The amount of total lactic and heterotrophic bacteria, the enzymatic activity and the intestinal morphometry did not differ between dietary treatments. The results demonstrate that fermentation with Lactobacillus acidophilus enables greater inclusion of soybean protein in South American catfish diets and promotes the control of intestinal pathogenic bacteria.

Keywords: digestive enzymes; fermented soybean; fish nutrition; intestinal histomorphometry.

Figure 1

Lactic acid bacteria count (A), amylase activity (B), protease activity (C) and soluble protein (D) of soybean meal fermented with Lactobacillus acidophilus (SMFL) at different times of fermentation. Lactic acid bacteria count (CFU g⁻¹): y = −0.001x² + 0.1752x − 0.5475, R² = 0.86, p = 0.002. Amylase activity (U g⁻¹): y = −0.000041x² + 0.0062x − 0.0438, R² = 0.56, p = 0.0106. Protease activity (U g⁻¹): y = 0.000075 + 0.00736, R² = 0.67, p < 0.0001. Soluble protein (mg g⁻¹): y = 0.2830x + 22.6624, R² = 0.85 p < 0.0001.

Figure 1

Lactic acid bacteria count (A), amylase activity (B), protease activity (C) and soluble protein (D) of soybean meal fermented with Lactobacillus acidophilus (SMFL) at different times of fermentation. Lactic acid bacteria count (CFU g⁻¹): y = −0.001x² + 0.1752x − 0.5475, R² = 0.86, p = 0.002. Amylase activity (U g⁻¹): y = −0.000041x² + 0.0062x − 0.0438, R² = 0.56, p = 0.0106. Protease activity (U g⁻¹): y = 0.000075 + 0.00736, R² = 0.67, p < 0.0001. Soluble protein (mg g⁻¹): y = 0.2830x + 22.6624, R² = 0.85 p < 0.0001.

Figure 2

Weight gain (A), specific growth rate (SGR) (B) and feed conversion (C) of South American catfish fed with diets containing different levels of soybean meal fermented by Lactobacillus acidophilus (SMFL). Weight gain: Y = 28.9506 − 1.5489(X − 21.6785), Y = 28.9506 when X < 21.6785. The breakpoint of the broken line is 21.6% (p = 0.0002). SGR: Y = 4.2187 − 0.1134(X − 21.0458), Y = 4.2187 when X < 21.0458. The breakpoint of the broken line is 21.04% (p < 0.0001). Feed conversion: Y = 1.1106 + 0.0326(X − 22.8846), Y = 1.1106 when X < 22.8846. The breakpoint of the broken line is 22.8% (p = 0.0178).

Figure 3

Count of Vibrionaceae (CFU g⁻¹) in the intestine of South American catfish fed with diets containing different levels of soybean meal fermented by Lactobacillus acidophilus. Y = 0.0053x² − 0.1484 + 3.6279, R² = 0.2755, p = 0.0316.