Peripheral blood of trout contained two populations of red cells: those with polyribosomes located in the cytoplasm, and those without polyribosomes. Starvation of trout for 30 days was accompanied by a proportional decline of the polyribosomal-containing (PRC) red cells. One week after a 15% bleeding of both fed and starved animals fed individuals showed a proportional decline of PRC red cells whilst starved fish showed a proportional increase of the same cell population. In fed individuals the bleeding response was accompanied by the appearance of many red cells with senescence-related characteristics. PRC cells in both groups of animals were arbitrarily subdivided into three subgroups according to the density of polyribosomes present. No statistically demonstrable differences were evident between the means of the three PRC cell groups of control animals and those subjected to starvation and bleeding. However, there was an apparent rise in the proportion of red cells with the highest density of polyribosomes as a result of both treatments.