CLARKE: FEEDINC. HABITS OF STOMIATOID FISHES 



afternoon (when two of the day trawls were 

 made) the next day. Vinciguerria nimbaria 

 could conceivably undertake short, irregular 

 excursions to shallower water during the day, or 

 alternatively, may have a strong preference for 

 rare, but perhaps vulnerable "stragglers" from 

 populations with shallower centers of abun- 

 dance. 



For several prey types, most of the items re- 

 corded were found together in one or a few of the 

 fish examined. This indicates that V. nimbaria 

 often feeds on patches or aggregations of certain 

 prey types. My earlier observation (Clarke 1978) 

 that V. nimbaria stomachs tend to be either quite 

 full or nearly empty throughout the day is also 

 indicative of encounters with patches of prey. 

 Since patchiness would increase the variability 

 of encounter rates by both individual fish and the 

 plankton nets, this might explain why some prey 

 types were poorly represented by the few plank- 

 ton samples as well as the large apparent differ- 

 ences in diet between small samples of fish. 



Wherever and however V. nimbaria feeds, it 

 clearly showed preference for certain prey types. 

 Some types which were abundant in the zoo- 

 plankton samples, e.g., Oncaea spp., Clausocal- 

 anus spp., small ostracods, were eaten frequently 

 by fish <30 mm SL; but many other types, e.g., 

 Eucalanus spp., scolecithricids (except Scoleci- 

 thrix danae), Metridia spp., large Pleuromamma 

 spp., and chaetognaths, also abundant were 

 either absent or poorly represented in the diet. 

 The types poorly represented in the diet were 

 mostly either larger, less pigmented, or more 

 translucent than those frequently eaten, regard- 

 less of whether the latter were rare or abundant 

 in the plankton. The diet and apparent prefer- 

 ences of small V. nimbaria are most similar to 

 but not identical with myctophids such as Ben- 

 thosema suborbital and Bolinichthys longipes 

 which feed on small zooplankton (Clarke 1980). 

 Vinciguerria nimbaria >30 mm SL showed 

 apparent preference for Stylocheiron spp. and 

 amphipods, both of which were rather uncom- 

 mon within the day depth range. In contrast to 

 both the remaining planktivorous stomiatoids 

 and several myctophids which also feed on large 

 zooplankton (see below), V. nimbaria ignored the 

 large calanoids which were fairly abundant at 

 the deeper end of its depth range (Table 2). 



The diets of the remaining planktivorous sto- 

 miatoids were nearly restricted to large cala- 

 noids and small euphausiids. The cope pods eaten 

 were fairly abundant within the day depth 



ranges of the fishes (Table 2), but were appar- 

 ently preferred over similar-sized Eucalanus 

 spp., augaptilids, and chaetognaths which were 

 also fairly abundant. The latter types are very 

 translucent compared with the types eaten and 

 probably less detectable visually. The Gonosto- 

 ma spp. and D. taenia have relatively smaller 

 eyes than V. nimbaria (data given in Grey 1964). 

 Thus, the apparent preferences of these gono- 

 stomatids may result from their being poorly 

 equipped to detect small, translucent, or other- 

 wise less visible prey. (The sternoptychid species 

 both have relatively large eyes, but they are 

 tubular and directed upward, and are difficult to 

 compare with the others.) 



The diets of the planktivorous stomiatoids ex- 

 cept Vinciguerria spp. were not only similar to 

 each other but to those of three common mycto- 

 phids {Lampanyctus nobilis, L. steinbecki, and 

 Triphoturus nigrescens), which also have rela- 

 tively small eyes (Clarke 1980). Limited data on 

 diet from Clarke (1978) indicates that the abun- 

 dant myctophids of the Lampanyctus niger spe- 

 cies group also feed similarly. Thus, although 

 they feed at different depths and times, several 

 coexisting species of fishes are utilizing the same 

 resources and apparently feeding selectively for 

 the same reasons; conversely, a relatively few 

 species of large zooplankton — particularly P. 

 xiphias and Euphausia spp. — are supporting a 

 large fraction of the planktivorous fishes. Cer- 

 tain small zooplankton, e.g., Oncaea spp. and P. 

 gracilis, also appear to be heavily grazed by Vin- 

 ciguerria and several other fishes from the same 

 area (Clarke 1980), but overall there is less inter- 

 specific overlap in diet and more evidence of dif- 

 ferent feeding mechanisms among species which 

 eat small zooplankton. 



Gonostoma elongatum, G. ebelingi, and D. tae- 

 nia appear to be essentially planktivores that 

 consume some large prey simply because they 

 reach larger sizes than do the other planktivor- 

 ous stomiatoids. All three have well-developed 

 gill rakers, none have large fangs, and the car- 

 diac portions of the stomach are not notably elon- 

 gate. Similarly, to the small individuals, the 

 large specimens usually contained several rela- 

 tively small prey; relative size of most items was 

 ca. 10% of SL with few over 20%. Most of the prey 

 were crustaceans, euphausiids and sergistid 

 shrimps, but some fish and squid were taken. 

 The only evidence of selectivity was the repeated 

 occurrence of the relatively uncommon amphi- 

 pod, Vibilia spp., in D. taenia. 



299 



