Does chromic oxide (Cr2O3) affect faecal lipid and intestinal bacterial flora in Arctic charr. Salvelinus alpinus (L.)?

Abstract. Arctic charr. Salvelinus alpinus (L.), were fed a commercial diet with or without a supplement of 1% chromic oxide (Cr₂O₃) in fresh water at 8°C for 70 days. Supplementation of the diet with 1% chromic oxide did not affect the lipid composition of stomach contents, but did affect that of the faeces.
Highest total lipid content in faeces was observed when fish were fed on the diet supplemented with chromic oxide. The proportion of triacylglycerols and free fatty acids increased in the neutral lipid fraction. The level of the dietary fatty acids 16:0, 16:1 and 18:1 increased, while 20:1 (n-9), 22:1 (n-11) and 18:2 (n-6) decreased significantly (P < 0·05) compared to the unsupplemented diet.
Total viable counts (TVC) of aerobic microorganisms were somewhat higher in stomach contents when the charr were fed on the unsupplemented diet. In faeces from charr fed the unsupplemented diet, TVC were higher, by a factor of 10 compared to fish fed diet supplemented with chromic oxide. Bacterial composition in stomach content of both rearing groups were dominated by Pseudomonas sp. and Agrobacterium sp., but the number of Lactobacillus sp. and Streptococcus sp. enhanced in stomach content when the fish were fed on the chromic oxide enriched diet. The faecal bacterial flora were also different between the rearing groups. The predominant bacterial species present in the faeces of fish fed unsupplemented diet were identified as Pseudomonas sp. and Aeromonas sp. Other bacterial species isolated included Lactobacillus sp., Streptococcus sp., Agrobacterium sp., Flavobacterium sp. and Vibrio sp. In contrast, the bacteria flora in faeces of fish fed the chromic oxide diet was dominated by the Gram-positive bacteria Streptococcus and Lactobacillus.
It is suggested that the use of chromic oxide as a marker in digestibility studies in Arctic charr may not be ideal.