Generally, the higher the level of blood glucose the steeper the diffusion gradient from the plasma space to the intracellular space of erythrocytes. In tambaqui (Colossoma macropomum), I have seen in a recent experiment, a reduction in the number of erythrocytes when the fish are hyperglycemic. In addition to a relative impermeability to glucose, is there any other explanation for the reduction in the number of erythrocytes in hyperglycemic tambaqui?