Morphological aspects of intestinal cells from gilthead seabream ( Sparus aurata) fed diets containing different lipid sources

Abstract

The aim of the present study was to evaluate the morphological changes in the intestine of gilthead seabream fed different lipid sources. Five experimental diets containing 22% lipid and 45% crude protein were formulated: the control diet included fish oil as the only lipid source, whereas the other four diets contained linseed, soybean or rapeseed oils at two different levels of fish oil substitution, 60% or 80%. Gilthead seabream juveniles of 79 g mean body weight were fed the experimental diets for 3 months. At the end of experiment, samples of anterior intestine were taken for ultrastructural study. A morphometric study was performed to complete the morphological results. Irreversible tissue damages (necrosis or cell degeneration) could not be found in the intestinal epithelium of fish, regardless the diet fed. Microvillis were well developed, among which some absorptive vesicles were observed in fish from all diets. The major ultrastructural differences in the enterocytes of fish fed different diets were the accumulation of supranuclear lipid droplets and the formation of lipoproteins. Lipid droplet accumulation was increased by the percent of fish oil replaced. The morphometric study revealed that the cellular space occupied by lipid droplets was 2.3 times higher when fish were fed a diet containing linseed or soybean oils at a 60% replacement level than in the control fish, whereas in fish fed the vegetable oils at a 80% replacement level and rapeseed at 60% it was 5 times higher than in the control fish. In the intercellular spaces and lamina propria two different classes of lipoproteins in relation to their size were found: very low density lipoproteins (VLDL) of 30 to 85 nm in diameter and chylomicrons (QM) of over 100 nm. Fish fed a soybean oil diet, particularly at a 60% replacement level, exhibited a much higher accumulation of these granules in dilated intercellular spaces. The rest of experimental groups showed chylomicrons as the main lipoprotein. These results are discussed in relation to fatty acid compositions and cellular mechanisms involved in lipid absorption.