Myctophum aurolaternatum 



Garman, 1899 



Fig. 47 — Myctophum aurolaternatum, male. 

 From Bolin (1939, p. 108, fig. 10). 



Description 



Counts for M. aurolaternatum (Table 9) vary significantly between areas of its total range, 

 particularly between three sectors of the eastern Pacific Ocean. 



SAO series in a straight line: SAO, over or slightly behind 'V0^. Pol well before base of 

 adipose fin. Prc2 only slightly elevated. Exposed margins of all scales smooth. Posterodorsal 

 margin of operculum rounded, increasingly striate and serrate with size, beginning at about 

 30 mm. Usually 2 AOp over anal base. 



Supracaudal luminous glands of males with 6 to 9 triangular, overlapping scales that 

 begin to form at about 50 mm; infracaudal glands of females with 3 to 7 rounded, usually 

 contiguous luminous scales, evident at 55 to 60 mm. 



Size: To about 105 mm. 



Least depth of capture: At surface at night. 



Distribution: Widely distributed: commonly taken from about 25° N to 17° S in the ex- 

 treme eastern Pacific Ocean (Fig. 48) but much less common in the central and far western 

 Pacific, or these areas are inadequately collected. Also common in the Indo-Pacific region and 

 Indian Ocean. The scarcity of captures in the far western Pacific may not be due entirely to a 

 lack of collecting effort. V. E. Becker (personal communication) has stated that the expeditions 

 of the Vitiaz did not find M. aurolaternatum between 180° and 150° E. Becker also stated that 

 206 specimens (from 73 stations) were taken in the Indian Ocean from Zanzibar and the Gulf of 

 Aden to the Andaman Islands and Bali. 



Discussion 



The distribution of M. aurolaternatum in the eastern Pacific Ocean (Fig. 48) is similar to 

 that reported by Wisner ( 1963a) for Lampanyctus omostigma and L. parvicauda ; those dis- 

 tributions appeared to coincide with the pronounced oxygen-minimum layer which underlies 

 much of the eastern tropical Pacific (Austin, 1960, Wyrtki, 1967). The latter two species were 

 mostly taken at depth, but virtually all specimens of M. aurolaternatum were taken with dip 

 net and surface light; possibly this species spends the daylight hours in or at least near the 

 upper limits of the oxygen-minimum layer. 



In the eastern sector, east of about 145° W, a pronounced racial or population structure is 

 evident in specimens from between about 25° N and 17° S. Highly significant differences occur 

 in nearly all meristic characters between three contiguous groups of specimens (24°29' N to 

 11°30' N, 11°29' Nto00°30' N, and 00°30' Stol7°17' S). These differences form a definite 

 clinical trend in all characters, the counts averaging lower in the north and grading rather 

 evenly into higher counts in the south. Differences in meristic characters are relatively slight 

 in specimens from the remaining areas (the mid-Pacific and westward through the Indian 



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