| Triploid fish were used to investigate the physiological importance of cell volume. In the absence of shape change, triploid red blood cells, which are larger than conspecific diploid red blood cells, should have a reduced surface area to volume ratio relative to diploid cells. In order to confirm this, surface area to volume ratio was measured from transmission electron micrographs of profiles of thin-sectioned diploid and triploid Atlantic salmon (Salmo salar) red blood cells. Surface area to volume ratio of triploid cells was 17% less than that of diploid cells, which likely reduces gas diffusion rates across the triploid red blood cell membrane and thus the oxygen carrying capacity of the fish. The larger volume of triploid red blood cells also likely affects blood cell passage through the microvasculature, where vessel dimensions are smaller than cellular dimensions. Passage through constrictive areas and its effects on circulating triploid red blood cells were evaluated by filtering suspensions of diploid and triploid Atlantic salmon and brook trout (Salvelinus fontinalis) red blood cells through Nucleopore filters of 8μm pore diameter. Filtration rate of triploid samples was 33-35% slower than diploid samples, confirming that triploid red blood cells encounter greater resistance to filtration. This may reflect greater resistance to passage through the microvasculature in triploid fish. The resultant increased effort required for the triploid heart to circulate the blood may increase demands of circulation on the standard metabolic rate. Along with surface area to volume ratio-induced reduction in oxygen carrying capacity, this likely contributes to reports of decreased metabolic scope and aerobic fitness of triploid fish. |
