Effects of plant-based diets on the bacterial counts and bacterial community composition of beluga sturgeon (Huso huso)

BACKGROUND: In recent years, many studies have been conducted on finding a suitable replacement for fish meal to supply the needs of aquaculture feed industry. Objectives: The present study was performed to examine the effect of replacing fish meal and fish oil with plant sources on bacterial counts in intestinal contents and mucus and bacterial composition in Beluga sturgeon. Methods: Beluga sturgeons with a mean initial weight of 133±5 g were distributed into 18 (300 L) tanks (30fish/tank) and were fed experimental diets for 60 days. The control diet contained only fish meal and fish oil as the primary source of protein and lipid, while the experimental diets contained 0, 40, 60, 80 and 100 percent plant protein sources (wheat gluten, corn gluten and soybean meal) and 20% vegetable oil blend (canola, sunflower, cotton and safflower oils) respectively. Results: Results showed that replacement of 80% fish meal and fish oil with plant sources didn’t have significant effect on final weight (235 ± 17 g) compared to control group (256.1 ± 10 g) in a 60 days trial. Replacement of fish meal with 100% plant proteins in combination with 80% vegetable oils resulted in significantly lower final weight (225.7 ± 11 g), compared to other treatments including control group (p<0.05). Replacing 80% fish oil with vegetable oils resulted in a significant reduction of bacterial count in intestinal contents and a significant increase in percentage of Entrobacteriacea sp. However, no significant differences were detected in bacterial counts of mucus in experimental treatments compared to control (p>0.05). Replacement of 60, 80 and 100% fish meal and 80% fish oil with plant sources significantly decreased bacterial counts in intestinal contents and intestinal mucosa compared to control group (p<0.05). Also this replacement cause significant change in bacterial composition of intestine. Conclusions: The results suggested that using plant sources in juvenile Beluga sturgeon diet decreases the bacterial count in the intestinal contents and mucus and changes the composition of intestinal micro flora.