3.4. Intestinal histology
The histological evaluation of fish distal intestine revealed that a healthy intestinal wall consisted of four primary layers: epithelial mucosa with abundant villi (mucosal folds) and numerous goblet cells, sub-epithelial mucosa, muscularis and serosa (Fig. 1a).
A progressive development of distinct morphological changes in the distal intestine of fish was observed to occur as the
level of FM replacement increased, with the most overt changes observed in fish from the FM20 treatment.
This treatment obtained scores of 5 for nearly all parameters evaluated. These differences represented an overall loss of
tissue integrity, most notably: changes in mucosal fold width/heights, a reduction in the number of supranuclear vacuoles, slight widening of the sub-epithelial mucosa, reduced/smaller goblet cells and widening of the lamina propria (Fig. 1).
The frequency of scores (%) to assess the presence of enteritis in fish from the four dietary treatments is shown in Table 7.