THE DISTRIBUTION OF CERATIAS HOLBOLLI 2S 



' Mancalias uranoscopus' was replaced in the south by distinct species. It is now seen that the single 

 species Ceratias holbolli is a cosmopolitan form, dwelling in all the oceans and extending into polar 

 latitudes, both north and south. A remark of Regan's referring to the Ceratioidea generally (1926, p. 10) 

 may be recalled: ' . . .it would be unsafe to predict that any species would not turn up anywhere.' 



VERTICAL DISTRIBUTION 

 Regan & Trewavas (1932) and Gregory & Conrad (1936) both give the vertical distribution among 

 Ceratioidea as 500-1500 m. Waterman (1938) extends the lower limit to 5000 m. However, with 

 regard to C. holbolli, there appears no definite evidence that the species extends below 1000 m. In 

 Table 3, the data showing depth of haul in metres, or metres of wire out, gives figures down to 4400 m. ; 

 but on only two occasions can one be certain that closing nets were used and that the specimens were 

 not taken at some intermediate depth when hauling in the gear. Of these two hauls, the deeper was 

 made in the tropical latitude of Hawaii (22 N) at 900-1000 m. when specimen no. 16 (Table 3 and 

 Fig. 6) was obtained. The upper limit of the range is to be found in high northern latitudes off the 

 coasts of Iceland and Greenland, where fishing trawlers took at least nine of the thirteen adults 

 recovered from the northern hemisphere. Soundings are only available in connexion with four of these 

 trawled fish; they were taken in water between 330 and 120 m. deep (Table 3). Any of these specimens 

 may, of course, have been captured somewhere between these depths and the surface. That such fishes, 

 taken in comparatively shallow water, were probably not moribund nor ' out of their depth ', is suggested 

 by the presence of a freshly swallowed Gadus esmarki in the stomach of one of them(Saemundsson, 1922). 

 This appears to indicate a normal feeding migration. 



The known bathymetric range of Ceratias holbolli is thus from 1000 to 120 m. or less from the surface. 

 This range implies a tolerance of extensive changes in hydrostatic pressure which the fish, lacking the 

 embarrassment of a swim-bladder, would appear well fitted to possess. 



TROPICAL SUBMERGENCE 



The presence of C. holbolli so near to the surface in high northern (and possibly southern) latitudes 

 can be explained, as in the case of certain other bathypelagic fishes, by the phenomenon of tropical 

 submergence (Hjort, 1912, p. 623; Sverdrup, Johnson & Fleming, 1942, p. 849). This would also 

 account for the widespread distribution of the fish and its vertical range. C. holbolli in the high 

 latitudes of both hemispheres probably has a normal vertical distribution from considerable depths 

 nearly to the surface, but its upper limit is increasingly submerged with approach to the equator. 

 Table 3 shows that in the tropics it has been taken at 900 to 1000 m., but it has never in such latitudes 

 appeared in a haul made from less than 600 m. Probably, for any one latitude, its known vertical range 

 of around rooo m. is only attained in the polar seas, north and south. When near the surface in these 

 regions it would be normally over the deep ocean, which explains why it has been so seldom captured 

 by the Arctic trawlers, since they fish only the neritic seas and would only take occasional specimens 

 which have strayed on to the continental shelf. 



Tropical submergence is usually attributed to the distribution of temperature and (to a lesser degree) 

 of light, in the ocean. Viscosity is doubled by a 25 C. fall in temperature (Sverdrup et al. 1942, p. 69), 

 and it has been pointed out that the viscosity of the water is important in limiting the vertical distribu- 

 tion of certain copepods and small bathypelagic fishes (Hjort, 1912, p. 698 ; Coe, 1946). With regard to 

 C. holbolli it can be argued that even a fish of this size is perhaps limited to water of high viscosity, 

 because its sluggish habit requires an environment which will allow maximum support with the least 

 expenditure of muscular activity. The sluggish habit is suggested by the clumsy shape of the fish, its 

 poorly developed body musculature and the condition of the fins ; of the latter, the pelvics are absent, 



