Author(s): Sherif M El-Kadi and Ahmed M El-Morsy

Abstract: Nutrient utilization was evaluated in Nile tilapia (Oreochromis niloticus) where it was divided into four groups according to time of water replacing (after 2, 4, 6 and 8 days for control, T1, T2 and T3, respectively). Final protein efficiency ratio values of T1 were significantly higher than other groups (P<0.05). The best (lowest) mean feed conversion ratio (FCR) was obtained from T1, while it was in T1 non-significantly different ( >0.05) with control. The feed intake and protein intake showed similar values in all groups. The best Nutrient utilization parameters were in T1, which decreased the cost of fish production by decrease in the fuel consumption. The maximum value of total bacterial count was in the fish intestine in T3 being 1.96×10⁶ Colony Forming Unit (CFU) /g after 12 weeks. Yeast and fungal count in the fish intestine fluctuated between 0.05 and 12.2 ×10² CFU/g. Coliform count in the fish intestine up to the minimum values in the first week being 0.34, 0.23, 0.31 and 0.3 ×102 CFU/g in C1, T1, T2 and T3, respectively. Five different colonies of fungal isolates were identified as Aspergillus ochraceus, A. oryzae, A. niger, Geotrichum candidum and Penicillium sp.

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