CLARKE: ECOLOGY OF STOMIATOID FISHES 



a quite different size-depth pattern and tended to 

 co-occur with much larger individuals of its con- 

 geners. The former two species co-occurred 

 throughout much of their depth range with 

 similar-sized individuals of three species of the 

 myctophid genus Lampanyctus. Thus in the 

 100-250 m layer at night similar species of at least 

 two genera of two families co-occur. This is in 

 contrast to the upper 100 m where only rather 

 different or distantly related species co-occur. 



Other gonostomatids exhibited nighttime pat- 

 terns quite different from any of the other species 

 considered. Danaphos oculatus remained at the 

 day depth and showed no trend in size composition 

 with depth. Valenciennellus tripunctulatus 

 occurred much deeper than similar-sized indi- 

 viduals of any other species. Diplophos taenia 

 occurred much shallower, with respect to size, 

 than any of the species thus far investigated. It is 

 possible that some of the shallow-living myc- 

 tophids, e.g., Myctophum spp., which were not 

 adequately sampled by the trawl also have pat- 

 terns similar to that of Z). taenia. 



The larger stomiatoids with fanglike teeth, dor- 

 sal or mental "lures," or various adaptions for 

 swallowing large items, are generally thought to 

 be predators on small nekton. Near Hawaii, the 

 dominant "predatory" species exhibited a variety 

 of patterns at night. Astronesthes indicus, Chau- 

 liodus sloani, and Thysanactis dentex showed 

 trends for increased size with depth. In the upper 

 100 m, these species co-occurred with roughly 

 similar-sized or slightly smaller individuals of the 

 more abundant myctophids and Vinciguerria 

 nimbaria. Although there are, scattered through- 

 out the literature, several records of larger 

 stomiatoids ingesting rather large prey, it seems 

 unlikely that these three species are important 

 predators on the abundant fishes in the upper 100 

 m or that the latter are important items in the 

 former's diet. All sizes of Idiacanthus fasciola, 

 Eustomias bifilis. and Astronesthes splendidus 

 appeared to occur throughout their night depth 

 ranges. Thus it would seem that, if indeed any of 

 the larger stomiatoids are important predators on 

 the small fishes in the upper 100 m, species such as 

 these are more likely candidates. 



Malacosteus niger did not migrate, and its depth 

 range was somewhat deeper than the day ranges 

 of most of the vertically migrating species consid- 

 ered here. Malacosteus niger has very poorly de- 

 veloped serial, ventral-lateral photophores in 

 comparison with most other stomiatoids. The only 



nonmigrating species of myctophid, Taaning- 

 ichthys bathyphilus, occurs in the same depth 

 range and has greatly reduced serial photophores 

 in comparison with the other myctophid species. 

 If, as Clarke (1963) has suggested, ventral-lateral 

 photophores are a counter-shading device, their 

 absence or reduction in these deep-living, non- 

 migrating species is likely related to lower light 

 levels and more nearly spherical radiance dis- 

 tribution at such depths even during the day in 

 comparison to the regime which most of the mi- 

 gi'ating species experience day or night. 



Three of the species which occurred together at 

 400-600 m during the day, Danaphos oculatus, 

 Valenciennellus tripunctulatus, and Ichthyococ- 

 cus ovatus, all have dorsally directed eyes and 

 markedly ventrally directed serial photophores. 

 These characteristics are shared by the sternop- 

 tychids of the genus Argyropelecus which also 

 occur in the same depth range (S. S. Amesbury, 

 pers. commun.). The argentinoid, Opisthoproctus 

 soleatus, which shares the same day depth range, 

 also has dorsally directed eyes and a ventrally 

 directed luminescent apparatus. At night, none of 

 these species appear to undertake extensive mig- 

 rations. Danaphos oculatus remains at the same 

 depths, V. tripunctulatus undertakes a limited 

 upward migration, and /. ovatus either migrates 

 or disperses upward. The Argyropelecus spp. 

 either move upward slightly or remain at the 

 same depths (S. S. Amesbury, pers. commun.). 

 Opisthoproctus soleatus was for some reason 

 nearly absent from the night samples; out of the 

 114 specimens only 4 were taken at night. 



Several investigators (see review by McAllister, 

 1967) have suggested that the dorsally directed 

 eyes are an adaptation for better detection of prey 

 or predators above the fish and that the ventrally 

 directed light organs serve to disrupt the 

 silhouette of the fish to predators below. These 

 adaptive values would be realized only under a 

 situation where light levels were low but still 

 sufficient for vision and where the radiance dis- 

 tribution was dominated by the downwelling 

 component. Such conditions probably obtain only 

 during the day for the above species. This would 

 suggest that they feed primarily during the day 

 and that they are exposed to heavier predation 

 then also. At least the former seems likely. These 

 species probably feed on zooplankton, and pre- 

 liminary analyses of zooplankton in the study 

 area indicates that these species encounter higher 

 concentrations during the day owing to vertical 



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