Lipid digestibility and ultrastructural changes in the enterocytes of Arctic char (Salvelinus alpinus L.) fed linseed oil and soybean lecithin

Arctic char (Salvelinus alpinus L.) were fed two isocaloric diets supplemen ted with 15% linseed oil or soybean lecithin, and subsequently analysed for ultrastructural changes in various intestinal segments (pyloric caeca regi on, midgut and hindgut) as well as apparent digestibility coefficients (ADC ) of the diets. The ADC of dry matter, lipid and individual fatty acids wer e always highest in fish fed the soybean lecithin diet. In hindgut for exam ple, ADC of lipid and dry matter were 94 and 96%, respectively, in fish fed the soybean lecithin diet compared to 85 and 94% in fish fed linseed oil. There were major ultrastructural differences in the enterocytes between fis h fed the two experimental diets. In char fed the linseed oil diet there we re substantial accumulations of lipid droplets in the enterocytes from the pyloric caeca and midgut but not in hindgut. These accumulations were not o bserved in fish fed the soybean lecithin diet. In some cases, deposition of fat in the enterocytes was so great that it resulted in epithelial damage with lipid droplets and cell debris appearing in the intestinal lumen. Thes e changes are likely to be pathological and may lead to intestinal malfunct ion and represent a major infection route to pathogenic bacteria. On the ba sis of these results it is suggested that endogenous phospholipid synthesis is insufficient to maintain lipoprotein synthesis in Arctic char when fed diets containing high levels of polyunsaturated fatty acid of total lipid, and that phospholipids should be supplied with such diets.