I collected blood from several fish species in vacutainers with EDTA. After that, we centrifuged blood (4500 rotations / minute - 5 minutes). Blood cells of carp did not sediment.  On the other species (crucian carp, rudd, roach, chub), blood cells, have separated of plasma. I centrifuget again the common carp blood (10000 rot/min – 3 min) but we obtained the same result. I can not find an explanation!