168 VITAMIN D GROUP 



up they somehow accumulate it, at times losing part of their supply for 

 spawning, but on balance always gaining more. 



The function of the vitamin D in fish is unknown. If it is related to bone 

 calcification, the questions remain why different species require widely 

 different amounts of it, and why most species store much greater quantities 

 than do the marine mammals, such as seals and whales, which consume 

 them. Several investigators^^^ have associated a low vitamin D content in 

 the liver oil with imperfect bone formation in the so-called cartilaginous 

 fishes — elasmobranchs and cyclostomes — including representative sharks, 

 dogfish, skates, rays, chimeras, and lampreys. It is well established that in 

 these species the liver oil seldom contains as much as 100 I.U. of vitamin 

 D per gram, and usually much less. Examples are given in Table III. 

 It is evident, however, that some cartilaginous fishes store more vitamin 

 D than some fishes with hard bones; also that sturgeons, which are usually 

 classified as true fishes in spite of their skeletal softness, have the lowest 

 vitamin D content of all. 



The studies on the cartilaginous fishes marked the first correlation be- 

 tween zoological classification and vitamin D content. They were followed 

 by the work of Bills et al.,^''^ who made a taxonomic study of the distribution 

 of vitamins D and A in 100 species of fish (Table III). This work revealed 

 that several fishes of the order Percomorphi exhibit extraordinary concen- 

 trations of vitamin D in their livers (tunas, basses, and swordfish). On the 

 other hand, livers of fishes of the order Heterosomata, which includes the 

 halibuts, flounders, and other flatfish, were comparatively poor in vitamin 

 D, though rich in vitamin A. Livers of fishes of the order Cataphracti, the 

 rockfishes, were better than average sources of both vitamins. 



After Massengale and Nussmeier*^ in 1930 demonstrated that irradiated 

 ergosterol is less effective than cod liver oil, per rat unit for chicks, many 

 writers, especially in the medical field, were given to distinguishing the two 

 forms as "synthetic" and "natural." The implication was that the natural 

 vitamin D of fish oils was a single definite substance. That this is not so 

 w^as first shown in 1934 by Bills ei al."^ who found that a specimen of bluefin 

 tuna liver oil exhibited a chick-rat efficacy ratio of about 15, whereas the 

 ratio for cod liver oil was 100 and that for irradiated ergosterol was 1. 

 (The tuna species was described as Thunnus thynnus, the designation some- 



>" E. Poulsson, Strahlentherapie 34, 648 (1929); S. Schmidt -Nielsen and S. Schmidt- 

 Nielsen, Hoppe-Seyler's Z. physiol. Chem. 189, 229 (1930); R. K. Callow and C. F. 

 Fischmann, Biochem. J. 25, 1464 (1931) ; E. Andr4 and R. Lecoq, Compt. rend. 194, 

 912 (1932). 



178 C. E. Bills, F. G. McDonald, O. N. Massengale, M. Imboden, H. Hall, W. D. 

 Hergert, and J. C. Wallenmeyer, J. Biol. Chem. 109, Proc. vii (1935). 



"9 C. E. Bills, O. N. Massengale, and M. Imboden, Science 80, 596 (1934). 



