The article presents data about the physiological and biochemical assessment of a new three-breed carp cross. The basis for the creation of the cross was the theory of heterosis and the high combinational ability of both parent forms. The effect of heterosis was noted for a number of zootechnical indicators: body weight, head index, number of stamens on the anterior gill arch. The results of a comparative analysis of biochemical parameters such as alanine aminotransferase activity, glucose and total protein content are presented, which allowed us to conclude about the physiological state of the new three-breed cross, about the balance of its carbohydrate metabolism and high rates of protein metabolism, low level of hepatocyte destruction, high immune status and cellular immunity. The new cross is characterized by intensive metabolism of a greater proportion of mature neutrophils and a high level of cellular immunity according to the cytochemical coefficient of lysosomal cationic protein. When obtaining a new three-breed cross, the method of reciprocal hybridization of different carp breeds was used and the choice of an acceptable option with a pronounced effect of heterosis in terms of productivity and vitality was used. The article presents the results of immunological, hematological and biochemical blood tests of the new cross. Also, the article demonstrates the results of studies of the phagocytic activity of neutrophils and determines the content of non-enzymatic cationic protein in them. According to the results of the biochemical assessment, the new three-breed cross showed a high combination of its parent forms with the expected level of the heterosis effect.