Natural resistance of fishes is innate capacity of the organism to resist aggressive impact of pathogenic factors of biotic and a biotic nature, including pathogens of infectious and invasion disease and product of their vital activity (exo- and endo-toxins). Immune status is structural and functional state of immune system at the concrete stage of life cycle of species. The document consists of 4 Secs. Section 1 lays down general provisions. Section 2 classifies unspecific factors of immunity.