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In a completely randomized design, the effects of two probiotic bacteria, Bifidobacterium animalis and B. lactis at four concentrations of 0 (control), 1×10⁹ (T1), 2×10⁹ (T2) and 3×10⁹ (T3) CFU 100g^-1 on nutritional parameters of rainbow trout fry (0.538 ± 0.197 g body weight) were compared for 60 days, with each treatment carried in three replications. A significant difference was observed between treatments and the control in protein and lipid gain and also body composition (p<0.05). Despite a significant difference of metabolic growth rate in T1 and T2 with T3 and the control, no significant difference was observed between T3 and the control. The results demonstrated that the use of thesebacteria could improve nutritional parameters and metabolic growth rate of rainbow trout fry.

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In a completely randomized experiment, the effect of Daphnia magna meal on growth performance and carcass composition of rainbow trout (Oncorhynchus mykiss) larvae (body weight 0.538±0.197 g) was evaluated for a period of 60 days. Five diets with the same protein content (crude protein 52.70%) were prepared, including two diets containing fermented daphnia meal T₁ (20%), T₂ (30%), two diets containing raw meal T₃ (20%) and T₄ (30%), and a basal diet without daphnia meal as the control. The bacterial species used for fermenting included five commercial probiotic species. Fermented daphnia meal brought about significantly higher growth and the lowest feed conversion ratios, viz. T₁ (1.27 ± 0.35) and T₂ (1.31 ± 0.46), in comparison with T₃ (1.38 ± 0.37), T₄ (1.41 ± 0.42) and the control (1.84 ± 0.69) (p<0.05). The result of carcass composition analyzes showed that the highest protein percentage (68.23 ± 0.48%) was in T₂ and the highest percentage of fat and energy (11.26 ± 0.50% , 4761.63 ±48.88 Cal g^-1) were in T₄ (p<0.05). The overall results of this experiment indicated that daphnia could be considered as a suitable partial protein source in rainbow trout larval feed.