Yeast extract on growth, nutrient utilization and haemato-immunological responses of Nile tilapia

Dietary supplement anon 211, 40, 60, 80 g kg(-1)) of a nucleotide source (NuPro (R) was evaluated on growth, nutrient Utilization, ha haemato-immunological responses and resistance to experimental infection of Nile tilapia. Fish (2.63 +/- 0.63 g) were fed experimental diets to satiation three times a day for 75 days. Feed intake increased linearly with increasing levels of NuPro (R) promoting higher weight gain (P < 0.05). Survival, feed conversion and protein retention were riot affected. Following the growth trial, Fish were challenged with Acromonas hydrophila by intraperitoneal injection. Survival and innate immune responses (phagocytosis and lysozyme activity) were not significantly affected. However, among the haematological variables, thrombocyte, leucocyte and monocyte counts increased linearly (P < 0.05). The indirect measurement of digestibility in juvenile Nile tilapia (122.32 +/- 11 g) indicated a linear decrease in protein (1.410), dry matter (5.72%) and energy (4.10%) digestibility coefficients as dietary supplementation increased (P < 0.05). NuPro (R) showed to be a beneficial additive to he supplemented in diets for juvenile Nile tilapia, providing 32.8% increase in feed intake and 28.8% in weight gain, as well as in thrombocyte, leucocyte and monocyte counts in blood, possibly indicating a more efficient defence response in the highest dietary supplementation levels tested.