324 DISCOVERY REPORTS 



also appear to be true for Alepisaurus and Anotopterus. Our knowledge of the vertical distribution of 



the Scopelarchidae, Evermannella and Omosudis is less complete.) 



Fishes without a swim-bladder are heavier than their environment (Jones and Marshall (1953) have 

 reviewed the data on densities). The only pelagic fish that has been well studied is the mackerel, 

 Scomber scombrus with a density of 1-071 and a sinking-factor of 1043. * 



Very probably other pelagic fishes without a swim-bladder are also heavier than the surrounding 

 water, and, like the mackerel keep their level by unceasing activity. A study of their appearance and 

 food suggests that the Alepisauroidea are active swimmers and their lightly ossified skeletons may point 

 to their having lower sinking-factors than the mackerel. Moreover, Taylor's ( 1 92 1 ) work on the density 

 of fish tissues would indicate that the sinking-factor of any alepisauroid is likely to be more than 1000. 

 While there are no observations of swimming in alepisauroids which bear on this problem, it is in- 

 teresting that Skowron (1928), who studied the luminescence of Chauliodus shard, saw that these 

 fishes at first swam vigorously, but on ceasing active movements sank to the bottom of the container. 

 This, as I have seen in the Red Sea, is also true of Stomias affinis. Evidently both fishes are heavier 

 than the surrounding water, and it is significant that, like the alepisauroids, both are without a swim- 

 bladder. 



Ossification of the skeleton. Hubbs, Mead and Wilimovsky (1953) found no reason to accept Roule's 

 chimerical hypothesis that Ajiotopterus is a ' monstre normalise ' or ' teratobionte '. Nor is there evidence 

 that this fish or any other alepisauroid is rachitic. Their skeletons are rather delicately but not 

 abnormally built. 



A five foot Alepisaurus ferox weighs about 4 lb. (Lowe, 1835), a striking indication of its lightly 

 ossified skeleton as well as of its compressed and rather lean-looking body. Harry (1953 a) has drawn 

 attention to the peculiar cartilaginous development of the jaws in the Paralepididae and Anotopteridae. 

 Certainly, the long time of exposure required to get tolerably clear hard-tube X-ray photographs of 

 these fishes provides further evidence of the lack of calcification in the skeleton ; and this is also true 

 of Omosudis lowei (s.L. 60 mm.) Evermannella hyalinus (s.l. 153 mm.), Neoscopelarchoides elongatns 

 (s.l. 198 mm.) and N. dubius (s.l. 138 mm.). Only in Scopelarchus cavei sp.n. (s.l. 70 mm.) does the 

 degree of ossification of scales and skeleton compare with that, say, in a myctophid. 



Moreover, in some of the alepisauroids the calcification of the skeleton seems to be a slow, irregular 

 and protracted process. Beebe (1932) remarks that a post-larval Omosudis lowei of total length 

 1 1-45 mm. did not have ' . . . a particle of bone in the entire body, fins, fin-rays or appendicular skeleton 

 except for a faint trace in the centre of the supracleithrum '. The head bones, particularly the pre- 

 maxillae and dentary were well ossified. Similarly, in the large ' Benthalbella ' larvae of the scopel- 

 archids, the skeleton, except for the skull, has a soft, cartilaginous texture. In Anotopterus the thin, 

 scale-like segments along the lateral line canal (see Text-fig. 7) are only plainly visible in larger indi- 

 viduals. Maul (1946), who studied specimens from 265 mm. to 342 mm. in standard length, remarks 

 that, along the anterior half of one individual, they only became visible after alizarin staining. Lastly, in 

 certain paralepidids (Ege, 1930; Parr, 193 1 ; Harry, 1953 a), the scaling is not completed until very late 

 in development. I have also found this feature in Notolepis coatsi. 



Parr (1937) has suggested that the amount of available vitamin D falls off with increasing depth, 

 and that fishes living at deep levels in the ocean have developed lower requirements for this vitamin, 

 this resulting in less extensive ossification of the skeleton. But assuming vitamin D to be necessary 

 for the normal formation of bone in fishes, Anotopterus, Alepisaurus and the paralepidids live at levels 

 not very far removed from the phytoplankton-bearing, vitamin D-producing, upper layer of the ocean. 



, . . . r density of fish 



1 binking-factor = -j : ~ ; — - x 1000. 



density of environment 



