Caspary (1992) reported that increased intestinal villi leads to increased surface area for nutrient absorption, thereby
improving growth performance and feed utilization in animals. Several researchers proposed that fermentation of inulin
produces several substances that stimulate intestinal cell proliferation, which in turn results in increased villus height
(Blottiere et al., 2003; Rehman et al., 2007; Nabizadeh, 2012). The present study demonstrated that dietary supplementation
with inulin (5.0 g kg−1) and JA(5.0 g kg−1 and 10.0 g kg−1) resulted in greater villus heightin all parts ofthe intestine, although
a significant increase in villus height was observed only in the anterior and middle parts. However, the effect of dietary
inulin on carnivorous fish appears to be different. For example, Olsen et al. (2001) reported that a high level of dietary inulin
(150 g kg−1 dietary inclusion) had negative effects on the ultrastructure of the gastrointestinal tract of Arctic char (Salvelinus
alpinus). In addition, decreased microvillus height was observed in gilthead sea bream fed a diet that included 10.0 g kg−1
inulin (Cerezuela et al., 2013). Intestinal goblet cells synthesize mucin, which invades enteric pathogens. Thus, an increase
in intestinal goblet cell numbers would help prevent colonization by pathogenic bacteria and promote beneficial bacteria.
We found that the fish fed the 5.0 inulin diet and the 5.0 JA and 10.0 JA diets had a higher goblet cell number than the other
groups. In another study, however, dietary supplementation with inulin at 10.0 g kg−1 had a negative effect on the number
of goblet cells in gilthead sea bream (Cerezuela et al., 2013). These findings suggest that the beneficial effect of dietary inulin
on intestinal morphology might differ among species, especially those with different feeding habits. The data also show that
inulin and JA had comparable effects on villus height in Nile tilapia.
In conclusion,this study demonstrated the beneficial effects of inulin on growth performance and health status in juvenile
Nile tilapia. In addition, direct supplementation with JA had superior effects compared to those of inulin at the equivalent
inulin levels. The recommended levels of dietary supplementation with inulin and JA are the maximal levels tested (i.e.,
5 g kg−1 and 10 g kg−1, respectively).