z6 DISCOVERY REPORTS 



the pectorals much reduced, and the caudal, although large, yet palmate and weakly constructed.* 

 Such a fish might, in low latitudes, be confined to the deeper cold water; towards the poles, 

 where the temperature differs little throughout the water column, it could approach nearer to the 



Light intensity as a barrier to vertical range may, in this context, be even more important. Hjort 

 (1912 p 664) has written ' in different waters the upper limit for black fish and red crustaceans seems 

 to coincide with the same low intensity of light', and Sverdrup el al. (1942, p. 851) have also noticed 

 this direct effect of light upon certain bathypelagic organisms. The reduction and effective concealment 

 of the eye during the ontogeny of C. holbolli strongly suggests that the fish is nicely adjusted to the 

 intensity of light in its environment. It is probably adapted to surroundings of near or complete 

 darkness, and consequently must suffer submergence in the tropics, but could rise much nearer to the 

 surface, from the bathypelagic to the mesopelagic zone, progressively farther north and south as the 

 intensity of illumination decreases. There is also the possibility of a superimposed diurnal rhythm 

 which would bring the fish nearest to the surface at night. 



With regard to this matter there exists direct evidence that, in a high latitude, a bathypelagic fish can 

 make an apparently normal feeding migration to within a few feet of the very surface of the ocean. For 

 this information I am indebted to Dr N. A. Mackintosh, who observed the fish at St WS 540, on 

 27 January 193 1 , when the R.R.S. ' William Scoresby ' lay alongside pack-ice east of the South Sandwich 

 Islands in 57 55' S, 21 21' W. This was in the region of the South Sandwich Trench over water 

 between 4000 and 5000 m. deep. In the 17th Scientific Report from the 'William Scoresby', 1931 

 (unpublished), Dr Mackintosh records: 



' It is noteworthy that during the night, when the ship was stopped and the wind fallen away, an 

 eel-shaped Stomiatoid fish, with brilliant luminous organs and silvery scales, was feeding on the krill 

 close to the surface, and could be plainly seen by the light of a cargo cluster. We attempted to catch it 

 with a hand net, but without success.' 



The Biological Deck Log contains a further note by the late E. R. Gunther describing the feeding activity. Although 

 not strictly relevant it seems worth recording here. 



'From a pair of luminous organs in the orbital region, the fish (which was 9-12 inches in length) emitted a beam 

 of varying intensity, of strong blue light which shone directly forwards for a distance of about two feet. The fish had 

 the habit of lurking at a depth of 2-6 feet below the surface, poised at an angle of about 35-40 from the horizontal— 

 this gave the beam an upward tilt: occasionally the fish swam round and with a quick action snapped at the cloud 



of krill above it. 



'In its manner of lurking and of snapping prey it resembled the freshwater pike. From the anal region was^ seen 

 to trail a length of brown substance which, it was supposed, might have been either genital or faecal product. 



Bertelsen has noticed that several large representatives of the genera Himantolophus, Oneirodes and 

 Crvptopsaras, all of them known to have a more southerly distribution, have been recorded from water 

 over the continental shelf of Iceland and Greenland. Tropical submergence, therefore, may be 

 a feature of some other members of the Ceratioidea. 



DISTRIBUTION AND OCEAN CURRENTS 



Bertelsen, however, has advanced an explanation opposed to that of tropical submergence in order to 

 explain the presence of Ceratias holbolli and the other Ceratioids just mentioned, in the shelf water of 

 high latitudes. He considers that these large specimens are carried northward by the North Atlantic 

 Current until they meet the Polar Current when they are forced by the cold bottom water to seek lesser 



* Waterman (1948) notices similar characters in the Ceratioid GigantacHs, and, in its brain structure, finds further evidence 

 of weakly developed locomotor activity. 



