Larval feeding habits of Diaphus garmani and Myctophum asperum (Pisces: Myctophidae) in the transition region of the western North Pacific

Abstract

We examined the feeding habits of the 2 dominant myctophid larvae, Diaphus garmani and Myctophum asperum, in the transition region of the western North Pacific. The incidence of feeding by these 2 species was ∼10 times higher during the day than at night (66 to 71 % vs. 5 to 6 %), indicating that both larvae are daytime visual feeders. The prey of the 2 species were quite different: D. garmani depended mainly on appendicularian houses and copepod nauplii, while M. asperum fed mainly on ostracods and polychaetes. Prey size ingested increased with larval development, while niche breadth was independent of larval size, and did not change during development for either species. The average number of prey consumed by both larvae was 1 to 2 per gut, although an underestimate of prey number for D. garmani is possible owing to rapid digestion of fragile appendicularian houses. The number of prey was positively correlated with body length for D. garmani, but not for M. asperum. Competition for prey among these myctophid larvae and co-existing Japanese anchovy Engraulis japonicus larvae is unlikely because of their diet and habitat depth segregation.