Fish Red Blood Cells
Red blood cells are usually the most abundant cells
in fish blood (up to 3 million per mm3). They contain hemoglobin and largely function in carrying oxygen from the gills to the tissues. Like the erythrocytes of other no mammalian vertebrates, fish RBCs are elated and show a wide range of sizes among different species. Elas-branchs typically have larger RBCs, although fewer in number, thinnest. Even within the teleports, fishes having morethrocytes per milliliter of blood generally have smaller RBCs. With-this group the more active species tends to have more erythrocytes sedentary forms. Perhaps the smaller cell size in these forms presents a shorter mean diffusion path length for essentialiratory gases such as oxygen. Shorter path lengths and morerocytes would make the oxygen uptake at the gills and delivery the oxygen-requiring swimming muscles more efficient.
Because the oxygen demands of fish vary with stage of life history environmental conditions, the number of red blood cells per mille-varies as a way of balancing the energy costs of producing RBCsthose of pumping blood to the tissues. Blood that is low in Brusly has to be pumped through the body at a greater rate than blood that is high in RBCs, if the oxygen demand is high. Since Cameron (1975) has demonstrated, for three species of freshwater fish that theteleost heart requires up to 4.4% of the total energy of the fish the number of RBCs can have a significant effect on its overall energy balance, including growth, etc. Indeed, rainbow trout (Salons Gardner) experimentally made anemic show significant increases in the volume of blood pumped by the heart (cardiac output). However, when oxygen demands of tissues are relatively low, such as when water temperatures are low and the fish are not very active, large numbers of RBCs are not required and the number tends to drop (RBCs live up to 150 days, at least in trench [Tines tines],at 18°C.
Thus, in active fishes there are often seasonal changes in RBC production. For example, winter flounder (Pseudopleuronectes arnericanus) have a peak in RBC production inflate spring and early summer in waters off Maine. Cameron has shown that changes in RBC counts (and in total hemoglobin concentration, Hob) in pinfish (Lagoon rhomboids) are of some significance in meeting seasonal increases in respiratory demands. How-ever, he points out that other adjustments, in erythrocyte size and in the rate of blood circulation, would also be required to meet the nearly tenfold change in respiratory metabolism associated with seasonal temperature extremes. In the striped mullet (Niue cephalous) changes in RBC numbers and Hob are associated not only with seasonal tempera-true changes but also with spawning activity, with its’ high-energy demands. Increases in RBC number during the spawning season have also been recorded for fish as diverse as carp (Cypriz.zus carpio) and the cichlid Tilapia nucleated and show a wide range of sizes among different species. Elasmobranches typically have larger RBCs, although fewer in number, thanteleosts. Even within the teleports, fishes having more erythrocytes per milliliter of blood generally have smaller RBCs. With-in this group the more active species tend to have more erythrocytes than sedentary forms. Perhaps the smaller cell size in these active forms presents a shorter mean diffusion path length for essential respiratory gases such as oxygen. Shorter path lengths and more erythrocytes would make the oxygen uptake at the gills and delivery to the oxygen-requiring swimming muscles more efficient.
Because the oxygen demands of fish vary with stage of life history and environmental conditions, the number of red blood cells per mille-liter varies as a way of balancing the energy costs of producing RBCswith those of pumping blood to the tissues. Blood that is low in RBCsobviously has to be pumped through the body at a greater rate than so the phenomenon may be widespread amongteleosts. It is also worth noting that RBC counts may also be affectedly other environmental factors, particularly pollutants. Destruction of erythrocytes through the inhibition of vital metabolic pathways in the cell appears to be one of the reasons chlorine in water is so harmful to fish.