Changes in intestinal morphology and amino acid catabolism in common carp at mildly elevated temperature as affected by dietary mannanoligosaccharides

A study was conducted to evaluate whether dietary mannanoligosaccharides (MOS) modulate the effect of mildly elevated water temperature on intestinal morphology and some selected whole blood amino acids and acylcarnitines in common carp (Cyprinus carpio carpio). Twenty fish in 10 aquaria were randomly assigned to either a control diet or the same diet with 4 g/kg MOS. A 35-day period at ideal temperature (23.2 °C) was followed by 14 days at elevated temperature (26.1 °C). After both temperature periods, one fish per aquarium was euthanized for the intestinal morphology and whole blood analysis on free amino acids and carnitine esters. The elevated temperature period decreased the number of neutral (P=0.031) and acid (P=0.004) mucin-secreting goblet cells and tended to reduce (P=0.056) the fold height in the midgut, irrespective of MOS supplementation. In both periods, supplementation of MOS increased (P=0.035) the number of goblet cells in the hindgut, but other histomorphometries were unaffected. Free concentrations of whole blood amino acids were increased after the mildly elevated temperature period: valine (P=0.002), leucine (P=0.001), methionine (P<0.001), phenylalanine (P=0.001) and tyrosine (P=0.001), but not affected by MOS supplementation. None of the carnitine esters were altered by the elevated temperature except propionyl carnitine that was higher (P=0.003) after the mildly elevated temperature of 14 days. Supplementation of MOS only tended to reduce the tiglyl carnitine (P=0.069) and methylmalonyl carnitine (P=0.078) concentrations. The analysis of free amino acids and carnitine esters could not support the hypothesis that MOS counteracts depressing effects of elevated temperature on amino acid catabolism. In conclusion, moderate elevation of water temperature could lead to considerable changes in gut histology and metabolism.