Background - This study evaluated the performance, prevalence of ectoparasites and morpho-functional response of the liver and the branchiae of Nile tilapia (Oreochromis niloticus) raised on fish meal with added of the homeopathic complex Homeopatila 100® at different concentrations.Methods - Post-reversed juvenile Nile tilapia (O. niloticus) of the GIFT (Genetic Improvement of Farmed Tilapia) strain were used in this study. The performance, ectoparasite prevalence and parasite load in the branchiae and skin as well as the liver and branchial histology. Fish were randomly assigned to receive one of four treatments: control, 20 mL hydroalcoholic solution (alcohol 30° GL); 20 mL Homeopatila 100® per kg of meal; 40 mL Homeopatila 100® per kg of meal; or 60 mL of Homeopatila 100® per kg of meal, compared to control with out the addition of the complex. There were four replications per treatment type (16 experimental units total) at a density of 40 fish per m3 over a period of 57 days. The Kruskal–Wallis H test (p < 0.05) was employed to analyse the physical and chemical parameters of water as well as for parasite prevalence; whereas analysis of variance was used for liver performance. If the values were significant (p < 0.05), they were compared by Tukey's test. Multiple comparisons of averages were performed using Student's t test (p < 0.05).Results - There were no significant between the physical and chemical parameters of the water between the different groups at the end of the experiment. Significant differences (p < 0.05) in the mixed parasite conditions were found within the different Homeopatila 100® treatments. The hepatosomatic ratio of fish treated with Homeopatila 100® was significantly lower than that of fish from the control group. The best results in the liver and branchiae occurred in fish receiving Homeopatila 100® at 40 mL/kg in terms of the number of hepatocytes/mm2, the intercellular glycogenic behaviour, the rates of histological changes (hyperplasia, lamella fusion and telangiectasia) and the percentage of neutral and acidic mucin-producing cells.Conclusion - The addition of Homeopatila 100® at a concentration 40 mL per kg/meal to the diet of juvenile Nile tilapias resulted in improved hepatocytes and intracellular glycogen levels as well as the lowest mean rate of branchial histological changes with an increase in acidic mucin-producing cells compared to neutral mucin-producing cells, compared to control.