Why are the eyes of larval Black Dragonfish on stalks?

Larval Black Dragonfish are long, slender and transparent, with eyes on long stalks that can be up to half the length of the body.

Moser (1981) states: "If one assumes that the major causes of larval fish mortality are starvation, predation, and the interactions between them, and that feeding and predator avoidance are largely dependent on vision, then eye specializations that improve feeding efficiency and predator avoidance are to be expected."

"In contrast to the round cup-shaped eye which lies flat in the developing orbit, the elliptical eye would have an increased rotational ability around the long axis, thus enlarging the volume observable from a given point. The next stage would be the extension of the eyes on short stalks so that they lie just outside the margin of the eye. Such eyes could be even more freely rotated so that the observable volume would approach that of a sphere. Extension of the eyes on pedunculate stalks would further increase this volume."

The larval Black Dragonfish Idiacanthus atlanticus Brauer, 1906 is a fish that has taken this strategy to extremes.

Further reading

1. Brauer, A. 1906. Die Tiefsee-Fische. I. Systematischer Teil. In: C. Chun. Wissenschaftl. Ergebnisse der deutschen Tiefsee-Expedition "Valdivia," 1898-99. Jena. v. 15: 1-432, Pls. 1-18.
2. Moser, H.G. 1981. Morphological and Functional Aspects of Marine Fish Larvae in Lasker, R. 1981. Marine Fish Larvae. Morphology, Ecology, and Relation to Fisheries. Washington Sea Grant Program. Pp. 131.
3. Paxton, J.R., D.F. Hoese, G.R. Allen & J.E. Hanley. 1989. Zoological Catalogue of Australia Vol.7 Pisces Petromyzontidae to Carangidae. Canberra: Australian Biological Resources Survey. Pp. i-xii, 1-665.