Fish blood cells

Question

Why do fish blood cells contain a nucleus?

Answer 1

The short answer for any "why" question in physiology is that a particular adaptation confers an evolutionary advantage. Be aware that most non-mammalian animals have nucleated rbcs. Current theories are several. One is that losing the nucleus provides more space in the rbc, making more room for oxygen carrying hemoglobin.  Another is that lack of a nucleus makes rbc more deformable, allowing capillaries to be smaller.  Having a nucleus allows non-mammalian rbcs to synthesize proteins.  Experimental work has shown that fish rbcs are part of the fish immune system.

Answer 2

Hello there!

The presence of nucleus in any somatic, reproductive, or floating (corpuscles of blood) cells of an organism is a normal phenomenon. If you see the evolutionary trend among the vertebrates respectively in fishes, amphibians, reptiles, aves, and mammals then the size of RBC decreases but the number increases. So, the nucleus along with mitochondria present in the vertebrates except mammals help them in the maintenance of aerobic respiration thus leading towards the maximum life-span however in mammals nucleus and mitochondria are absent help them in carrying the anaerobic respiration thus leading towards maximum life-span.