Physiology of Finfish and Shellfish

2.2.10. Red Blood Cells (erythrocytes)

RBC (erythrocytes) is usually the most abundant cells in fish blood (upto 3 million/cubic millimeter). They contain haemoglobin and largely function in carrying oxygen from the gills to the tissues. Fish RBC’s are nucleated contains hb. Shows a wide range of sizes among different species. Elasmobranchs have larger red blood cells and fewer in number than teleosts. Even within teleosts, fishes having more erythrocytes/millimeter of blood generally have similar RBC’s. Mature red blood cells of fishes are oval, tiny and range in long diameter from 7µ in many fishes such as in certain wrasses to 36µ in the African lungfish. Enucleate RBC’s are rare but the proportion of immature, roundish RBC’s varies considerably in fishes. The more active forms tend to have more erythrocytes than sedentary forms.

Oxygen transport in blood depends on the iron compound, hb the respiratory pigment of the blood. The hb content in the blood varies with the number of erythrocytes present. The number of red blood cells in fishes varies with the life history stage, habits and environmental conditions.