EFFECTS OF PARTIAL REPLACEMENT OF DIETARY SOYBEAN MEAL BY AUTOCLAVED GUAR MEAL WITH OR WITHOUT SUPPLEMENTATION OF Β - MANNANASE ON GROWTH PERFORMANCE OF NILE TILAPIA (Oreochromis Niloticus)

A growth trial was conducted to evaluate the effects of replacing 5 or 15% of soybean meal with raw Guar meal, autoclaved Guar meal or autoclaved Guar meal supplemented the diet with β-mannanase (0.04%) on both growth performance and histological status of Nile tilapia fingerlings. Seven iso-nitrogenous (~32% crude protein) and iso-energetic (~3450 Kcal estimated digestible energy) were formulated. Each diet was randomly allocated to duplicate groups of fish in fiberglass tanks and each tank was stocked with 25 fingerlings (initial average body weight 1.98 ± 0.47g). Fish were hand fed the experimental diets four times per day for 60 days. For histopathological examination samples of small intestine were taken from fish in different groups. There was significant reduction in growth performance when fish fed diets containing raw Guar meal comparing to those fed the control diet (free of Guar meal). Irrespective of treatment, there were no significant differences in term of growth performance between groups of fish fed diets containing Guar meal with either 5% or 15% inclusion level except in term of weight gain.                 Irrespective of inclusion levels, better performance of fish were observed when fish fed on control diet (diet 1) or diets supplemented with β-mannanase and contained autoclaved Guar meal followed by those fed autoclaved Guar meal without enzyme supplementation, while the worst performance was observed by groups of fish fed diets containing raw Guar meal.                 Histopathological study showed that feeding fish diet contained 15% raw Guar meal caused necrosis of the lining mucosa of the small intestine accompanied with infiltration of the inflammatory cells, this status was improved when fish fed diets contained autoclaved Guar meal and more improvement (increase in the number of goblet cells) in intestinal status was observed in group of fish fed diet supplemented with 0.04% β-mannanase and contained 15% autoclaved Guar meal. Through an economic standing point although, the relative economical efficiency for using Guar meal supplemented with enzyme is compatible with control diet containing soy bean meal, yet in term of net revenue (LE) it is clear that the diet free of Guar meal is still better to be used than any of the diets containing Guar meal. However, at the same time and through the results of this study, supplementing tilapia diets contained autoclaved Guar meal up to 15% with β-mannanase may be considered as a reliable dietary protein source.