Improved feed utilization,intestinal mucus production and immune parameters in sea bass (Dicentrarchus labrax) fed mannan oligosaccharides (MOS)

In the present study, the effects of dose dietary administration of mannan oligosaccharides (MOS) (Bio‐Mos; Alltech Inc.) on growth, digestibility, liver morphology, lipid and carbohydrate metabolism enzymes, organoleptic properties, immune parameters and gastrointestinal tract mucus production were assessed. MOS dietary inclusion significantly reduced lipogenic enzymes activity in liver and resulted in a lower lipid vacuolization and more regular‐shaped morphology of hepatocytes around the sinusoidal spaces, which could be associated to a better energy and feed utilization because of the improvement of feed utilization and the reduction of feed intake found in the current experiment. Moreover, MOS inclusion enhanced phagocytic activity of head kidney leukocytes in fish fed 4 and 6 g kg^?1 MOS diets at days 30, 45 and 60. Gut quantitative morphological analyses showed a marked dose‐dependent enhancement in the number of cells secreting acid mucins by unit of area which could be related to the previous improvement in resistance to bacterial infection. No effects on sensorial parameters and biochemical composition of flesh were detected.