. Therefore, the superior growth performances of fish fed the diets containing JA might be due to the differences in degree of polymerization of inulin sources and other substances in addition to inulin and FOS. JA contained high proportion of shorter fructan comparing to inulin from chicory. While high proportion (43–52%) of furctan in JA were short chain fructan (<9 degree of polymerization (dp)), 64–71% of fructan in inulin were medium chain fructan (10–40 dp) (Moshfegh et al., 1999; for review, see Kays and Nottingham, 2007). Although both inulin and FOS exert prebiotic effects, they showed several different prebiotic effects. For example, in fecal cultures, inulin and FOS affected the major fermentation products. Butyric acid was the major product of inulin fermentation whereas FOS fermentation mainly generated acetic acid and lactic acid (Rossi et al., 2005). Comparative study on prebiotic effects in vitro between inulin and FOS revealed that they influenced different microbial community and proteolytic activity (van de Wiele et al., 2006). Dietary supplementation with either inulin or FOS had similar effects on growth performance in rainbow trout (Ortiz et al., 2013), whereas supplementation with FOS had a more positive effect than inulin on the growth rate of turbot larvae (Mahious et al., 2006b). Other substances such as micronutrients in JA also may have had additional positive effects on growth response and feed utilization in juvenile Nile tilapia. In fact, JA contains various minerals and vitamins including iron, calcium, potassium, vitamin B complex, vitamin C, and vitamin A (Van Loo et al., 1995; Kays and Nottingham, 2007). Thus, direct supplementation with JA had positive effects on growth performance in Nile tilapia that were comparable to those of inulin.....
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