Feeding Ecology of Lanternfish (Pisces: Myctophidae) Larvae: Prey Preferences as a Reflection of Morphology

Larvae of 14 species of lanternfishes (Myctophidae) were examined to determine diet preference by taxa, size, and time. Feeding incidence was calculated from measures of gut fullness. Diet comparisons were based on the volume of prey consumed. All prey were measured along two dimensions and volume of prey was estimated from known morphology of items. The Bray-Curtis index of diet similarity resulted in six clusters, three of which were composed of a single species. The largest cluster of six species included members from the narrow-eyed subfamily Myctophinae. All species in this cluster exhibited a strong preference for ostracod prey with 84.4–96.6% (by volume) of their diet consisting of these prey. A second cluster included members of the genus Diaphus and three other species. These larvae preferred a diet of the various developmental stages of copepods. Two species, Lobianchia gemellarii (Cocco, 1838) and Hygophum taaningi Becker, 1965, formed a third cluster based upon their preference for gelatinous zooplankton. The three single species clusters included larvae with a variety of prey preferences. Hygophum benoiti (Cocco, 1838), in addition to calanoid copepods, ingested a relatively high percentage of protists. The diet of Lampanyctus alatus Goode and Bean, 1896 included prey from three broad categories: calanoid copepods, ostracods, and larvaceans. Larvae of Ceratoscopelus townsendi (Eigenmann and Eigenmann, 1889) also ingested a wide range of crustacean prey, but almost 20% of the diet consisted of thaliacean prey. Most larvae were diurnal predators, exhibiting relatively high feeding incidence from dawn to dusk with peak feeding between 1000 and 1500 hrs. One species, Myctophum selenops Tåning, 1928, continued to feed regardless of light availability. Prey size preferences were related to mouth size. The largest size range of prey was ingested by larvae with the largest jaw, and the smallest prey by larvae with the smallest jaw. Jaw length only affected the upper range of prey size; larger larvae also ingested a variety of smaller items.