Dietary galactooligosaccharide affects intestinal microbiota, stress resistance, and performance of Caspian roach (Rutilus rutilus) fry

• Very limited data on galactooligosaccharides (GOS) as prebiotic in aquaculture.
• GOS significantly increase Caspian roach fry resistance to salinity stress.
• Dietary GOS modulate the intestinal microbiota of Caspian roach fry.
• Dietary GOS as prebiotic increased lactic acid bacteria (LAB) levels in intestinal microbiota.
• GOS is a beneficial dietary supplement for improving the growth performance of Caspian roach fry.

The aim of this study was to assess the effects of galactooligosaccharide (GOS), on the growth performance, stress resistance and intestinal microbiota of Caspian roach (Rutilus rutilus) fry. Specimens (1.36 ± 0.03 g) were fed either a basal control diet (0% GOS, non-supplemented) or the basal diet supplemented with 1% and 2% of GOS. After 7 weeks of the feeding trials, growth factors (final weight, weight gain, specific growth rate, condition factor and food conversion ratio) as well as body composition, resistance to salinity stress and autochthonous intestinal microbiota were assessed. Results demonstrated that at the end of the trial growth factors (final weight, weight gain, SGR, FCR) were significantly higher in 2% GOS fed fish (P < 0.05). In addition, supplementation of GOS significantly increased both survival rate (P < 0.05), and resistance to a salinity stress challenge of prebiotic fed groups (P < 0.05). However, body composition and the total autochthonous intestinal heterotrophic bacteria counts remained unaffected in different treatments (P > 0.05). Nevertheless, autochthonous lactic acid bacteria levels were significantly elevated in fish fed 2% dietary GOS (P < 0.05). These results confirm that GOS improves growth performance, stress resistance and modulates intestinal microbiota by increasing lactic acid bacteria of Caspian roach fry, a very important fish species in the Caspian Sea.