This study investigated the protective effects of probiotic (Lactobacillus fermentum at a concentration of 10⁷ cells/kg feed), prebiotic (lactulose at 10 mL/kg feed), and synbiotic on the hematological and biochemical parameters of freshwater crayfish (Astacus leptodactylus) exposed to lead acetate (0.1 mg/L). For this purpose, 240 crayfish (with equal sex distribution) were divided into eight experimental groups with three replicates each (totaling 24 aquaria) as follows: control group (basal diet without supplement), three groups receiving probiotic, prebiotic, or synbiotic alone (without lead exposure), a lead-exposed group (basal diet without supplement), and three combined treatment groups (probiotic, prebiotic, or synbiotic together with lead exposure). The experiment lasted 28 days, after which hemolymph was sampled and hematological and biochemical changes were assessed. Results showed that lead exposure caused a significant decrease in total hemocyte count (including hyaline, granular, and semi-granular hemocytes). In contrast, administration of probiotic, prebiotic, and synbiotic led to a significant increase (p<0.05) in hemocyte counts. Furthermore, supplementation with probiotic, prebiotic, and synbiotic under lead exposure conditions exerted considerable protective effects on total hemocyte count as well as hyaline, granular, and semi-granular hemocyte populations, significantly elevating these parameters compared to the lead-exposed group without supplementation. Feeding with all three supplements following lead exposure restored total protein, albumin, glucose, and triglycerides to normal levels. Moreover, lactulose and the symbiotic reduced the toxic effect of lead on cholesterol, whereas the probiotic was unable to return cholesterol to the normal range. This study indicates that symbiotic supplementation can serve as an effective strategy to mitigate the toxic effects of heavy metals and maintain immune health in cultured crayfish.