In what part of the body is a shark's blood made? This was the subject of an enquiry that was recently sent to the Australian Museum.
Even after referring to several reference books, including my 'fish biology bible', Helfman et al (2009), I couldn't find out much about how blood was formed in sharks, so I contacted Dr Stuart Fraser, a colleague who works at the University of Sydney. Stuart replied:
"Not a lot is known about where blood cells are produced in sharks. In fact one review wrote “ At present, knowledge on the development of shark leucocytes and hematopoietic tissues is meagre”. It would appear that the spleen in the adult might have the most erythroid cells (red blood cells) while white blood cells are produced in an organ called the epigonal organ."
Again, I have to confess my ignorance. I had never heard of an 'epigonal organ'. I looked it up and found out that the epigonal organ is only found in sharks, and that there is one positioned underneath each kidney.
It seems there is much to learn about blood production in sharks ... feel free to comment!