A review with special emphasis on teleost fish bone

When comparing mammalian osteocyte-containing bone with anosteocytic ("acellular") fish bone, it is noteworthy that anosteocytic bone is capable of bone remodeling processes and participation in the organism's mineral homeostasis - two features that are attributed to osteocytic cells. As there is an evolutionary drift towards anosteocytic skeletons throughout teleost fish, osteocytic routes may either not been necessary any-more or it simply indicates that there are other non-osteocytic pathways. The lack of osteocytes in spite of osteoid produced by osteoblasts and bone matrix deposition in anosteocytic fish presumes that some mechanisms prevent the transformation of osteo blasts to osteocytes. The anosteocytic bone may form osteon-like structures, adapt to changing loading regimes and is subject to osteoclastic bone resorption. Considering the multiple types of osteocytic and anosteocytic bone matrices among teleost fish, the availability of mononucleated osteoclasts capable of bone resorption, high bone mineral density and an stabilizing mineralized notochord sheath, are only some observations that need to be studied further. Of note, there is evidence that intermediate stages between osteocytic and anosteocytic bone are present in some species. In fact, the European eel is one example that presents with effective multinucleated osteoclasts, small and few osteocyte lacunae with unknown network characteristics. Further investigation and imaging of osteocytic and non-osteocytic osseous structures will help to provide novel understanding of these essential characteristics in bone biology.