FISHERY BULLETIN: VOL. 78, NO. 3 



its prey. Even the smaller and therefore slower D. 

 atlanticus would have to detect prey only within 

 about 19 mm to search 1.0 m^ in the same time. 



Comparison of my results with those of other 

 studies is limited to generalizations due to differ- 

 ent methodologies. In most other studies, prey 

 items have been identified only to major taxa, bias 

 due to differential digestion has not been consid- 

 ered, and diets have not been compared with ap- 

 propriate estimates of available prey densities. 



Legand and Rivaton (1969) gave diets of nine 

 comparable species from the tropical Indian 

 Ocean. As near Hawaii, crustaceans dominated 

 the diets, and except for higher proportions of 

 amphipods and lower proportions of ostracods, 

 the diets of the myctophids were similar to those 

 of congeners from Hawaii. Ceratoscopelus 

 "townsendi" (which is probably really C. war- 

 mingi) had a wide variety of prey and with the two 

 Lampanyctus spp. had the highest frequency of 

 euphausiids. The diet of Benthosema simile, the 

 only species for which copepod genera were given, 

 was quite similar to that of B. suborbitale. Breg- 

 maceros macclellandi , unlike B. Japonicus from 

 Hawaii, had eaten no chaetognaths. Merrett and 

 Roe's (1974) data on three myctophid species from 

 the subtropical Atlantic also indicate that crusta- 

 ceans were the most important prey. Diets of the 

 individual species appear generally similar to 

 those of the most closely related species considered 

 from Hawaii. 



Gorelova (1978) found that migratory crusta- 

 ceans dominated the diets of both C. warmingi and 

 Bolinichthys longipes in the western equatorial 

 Pacific. The diet of small C warmingi was domi- 

 nated by copepods, and most items were <4 mm 

 long, but specimens of sizes comparable to those 

 examined in my study (40-90 mm total length) 

 had eaten a wider variety of prey, over 50% of 

 which (by weight) were >4 mm. The dominant 

 euphausiids were the large Thysanopoda and 

 Nematobrachion spp. The diet of all sizes of B. 

 longipes was dominated by copepods, and the 

 euphausiids eaten were mostly the smaller 

 Euphausia and Stylocheiron spp. Oncaea spp. 

 were much less important than near Hawaii. 

 Among the large copepods, however, candaciids 

 were the dominant type in both areas. Gorelova 

 (1977) noted that Lampanyctus and Triphoturus 

 (species not given) in the equatorial Pacific eat 

 euphausiids almost exclusively. 



Baird et al. (1975) showed that Diaphus 

 taaningi in the Cariaco Trench, like two Hawaiian 



Diaphus spp., ate a wide variety of prey, but in 

 contrast to all other species considered here or 

 elsewhere, the diet was heavily dominated by 

 Oikopleura. Since Oikopleura is probably ren- 

 dered unrecognizable in the stomach faster than 

 most of the other prey types, its importance in the 

 diet is probably even greater than Baird et al.'s 

 data indicate. Its frequency in the plankton from 

 the cod end of the trawl was much lower than in 

 the diet; however, it was probably under- 

 represented relative to larger forms in such a sam- 

 ple. Whether the dominance of Oikopleura reflects 

 a real preference or simply very high densities at 

 the depths where the fish were feeding cannot be 

 determined. 



Tyler and Percy (1975) investigated three 

 species of myctophids from off Oregon. The diets of 

 all three were heavily dominated by euphausiids, 

 mostly E. pacifica which was the most abundant 

 species in the area, and medium to large copepods, 

 the most frequently identified of which were 

 Calanus and Metridia spp. There was little indica- 

 tion of differences between fish species. Gjosaeter 

 (1973) showed similar results for another high 

 latitude myctophid, Benthosema glaciale; in this 

 case Thysanoessa spp. were the dominant 

 euphausiids. 



The results of most studies generally agree that, 

 with the obvious exception of D. taaningi, verti- 

 cally migrating fishes feed primarily upon rela- 

 tively large, probably more visible crustacean 

 zooplankton; however, the data for some species 

 considered here and by Gorelova (1978) indicate 

 that small juveniles graze the microzooplankton 

 more heavily than sizes considered by most 

 studies. In contrast to the neustonic myctophids, 

 e.g., Centrobranchus and certain Myctophum spp., 

 which feed primarily on shallow-living zooplank- 

 ton (Gorelova 1977), the principal prey of the 

 species considered here and by most other studies 

 undertake substantial diel vertical migrations 

 themselves (Brinton 1967; Roe 1972) — some al- 

 most as extensive as those of the fishes — and are 

 not present in the epipelagic by day. 



Though the diets of the 14 species considered 

 here show some general similarities, differences 

 in frequency of and preference for different prey 

 types indicate that most species are at least some- 

 what specialized. The discussion of diet and mor- 

 phology above points out unique features for most 

 species. Lampanyctus steinbecki, L. nobilis, 

 Triphoturus nigrescens, and Notolychnus val- 

 diviae were the only species which were very simi- 



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