The methods and results of determination of safety and relative biological value of carps (Cyprinus carpio) with philometroidosis and breams (Abramis brama) with ligulosis depending on infestation intensity with application of test-object Tetrahymena pyriformis realized in the conditions of the Republic of Belarus were presented. Research results showed that lowering of reproduction degree of protozoan on 20-30% could testify to the presence of light toxicity. Suppression of infusoria reproduction up to 30% with the simultaneous lowering of actions activity, disturbance of its character and availability up to 10% of inflected cells could testify on the moderate degree of toxicity. Lowering of infusoria reproduction degree on 30-50% with the simultaneous presence of 10-20% of cells with the affected character of motion, form and dead testified to evident toxicity of products. Lowering of infusoria toxicity on 50% and higher, presence of cysts, distorted cells, and ghosts testified to high product toxicity. Research results established that in case of high invasion intensity meat of carp philometroidosis had low toxicity (2 points). Meat of breams with ligulosis and moderate invasion intensity had low toxicity level (2 points), and in case high invasion intensity – moderate (3 points). The relative biological value in case of philometroidosis was on 13,29-28,41% lower in comparison with meat of healthy carps, and in case of ligulosis - on 18,66-57,29% in comparison with healthy breams meat