FISHERY BULLETIN: VOL 76, NO. 3 



well digested. Lampanyctus nobilis and L. stein- 

 becki occasionally take deep-living copepods dur- 

 ing the day, and C. warmingi apparently takes 

 large items whenever it encounters them. Still, 

 the instances of definite day feeding were so few in 

 even the latter three species that the medians and, 

 therefore the diel patterns, were only marginally 

 affected. 



All of these myctophids undergo diel changes in 

 temperature and prey concentration (Table 3) that 

 correlate with the observed pattern of feeding sole- 

 ly or mostly at night while in the upper 200 m. All 

 are at much higher temperatures at night. Al- 

 though some species occur as shallow as ca. 500- 

 600 m during the day and thus partially overlap 

 the daytime depth ranges of certain of their prey, 

 all occur below daytime maxima of prey concen- 

 trations and almost certainly encounter higher 

 concentrations at night. Certain details of the pat- 

 terns of stomach fullness indirectly indicate that 

 stomach evacuation rate may be lower during the 

 day as predicted by temperature differences. In 

 many species, stomach fullness did not clearly de- 

 crease during the day; since feeding rate was ap- 

 parently zero then, the evacuation rates must 

 have been low or zero. The sharpest declines in 

 stomach fullness occurred at or near dusk in most 

 species, near dawn in N. valdiviae and T. nigres- 

 cens, and during the night in H. proximum — not 

 during periods when the fishes remained within 

 their day depth ranges. In all cases except H. prox- 

 imum, however, something related to vertical 

 migration itself, e.g., activity, could be responsible 

 for the apparent increases in evacuation rates. 



Four species of stomiatoids, Gonostoma atlan- 

 ticum, Danaphos oculatus, Valenciennellus 

 tripunctulatus, and Vinciguerria nimharia, fed 

 only during the day. The last three species occur 

 somewhat shallower by day then do the myc- 

 tophids and are consequently at or near depths of 

 maximum concentration of their prey then. The 

 upward migration of V. nimbaria is similar in 

 extent to that of its prey. Thus this species en- 

 counters little or no diel change. Danophos 

 oculatus does not migrate, and Valenciennellus 

 tripunctulatus migrates less than do its prey. Con- 

 sequently, both species occur below high concen- 

 trations of prey at night. The adults of G. atlan- 

 ticum (as were most specimens used here) occur 

 near the lower depth limits of most prey species 

 both day and night, and the day-night difference is 

 probably minor. Thus in these species, the day 

 depth ranges, rather than the occurrence or up- 



508 



ward extent of migration, seem more related to 

 observed feeding pattern. 



All four species feed at nearly the same, low 

 temperature. Diel temperature change is zero for 

 D. oculatus, and relatively small for V. 

 tripunctulatus and large G. atlanticum because 

 they penetrate only part way through the ther- 

 mocline. Vinciguerria nimbaria undergoes a 

 change similar to that of the myctophids. The 

 temperature changes or lack thereof obviously 

 have no effect on feeding periodicity; however, the 

 steepness of the nighttime decline in stomach 

 fullness seems roughly correlated with nighttime 

 temperature indicating an effect on stomach 

 evacuation rates. This trend is considered in more 

 detail below. 



Lampanyctus niger and G. elongatum, the two 

 species which showed no diel pattern in stomach 

 fullness, do not undergo large diel changes in 

 either temperature or prey concentration in spite 

 of the fact that they migrate. The large individuals 

 of both species I as were all theL. niger and mostG. 

 elongatum) undergo a relatively small tempera- 

 ture change. Likewise, only the smallest juveniles 

 of either species encounter markedly higher prey 

 concentrations at night. The relatively low values 

 of stomach fullness in both species and the pres- 

 ence of deep-living, nonmigrating zooplankton in 

 L. niger indicate that these two species feed at a 

 low rate whenever and wherever they encounter 

 prey. 



Relationship to Previous Studies 



Comparison of the present results with those of 

 previous studies is restricted because method- 

 ology in all cases was different from that of the 

 present study and in many cases equivocal or 

 probably not sensitive enough to discern diel 

 trends or lack thereof. With the exception of the 

 study by DeWitt and Cailliet (1972), appropriate 

 statistical testing was not done, and it is impossi- 

 ble to do so from the published data. 



The most directly comparable study is that by 

 Holton (1967) on Lampanyctus (= Triphoturus) 

 mexicanus. Using 10 fish from each of eight 

 periods of the day, he determined dry weights, but 

 for some unknown reason weighed the entire 

 alimentary canal with the food. The minimal val- 

 ues observed, presumably from empty stomachs, 

 indicate that his "% nutrition" values should be 

 decreased by about 2.5-3 to make them roughly 

 comparable to those of the present study. Though 



