Early development of eye and retina in lanternfish larvae

Abstract

The morphological characteristics of the eyes and the retinae of lanternfish larvae of Lampanyctus crocodilus, Benthosema glaciale, and Myctophum punctatum were analyzed in pre-flexion, flexion, and post-flexion stages. Pre-flexion larvae of L. crocodilus, the species with the shallowest depth distribution, had spherical eyes located antero-laterally on a strongly laterally-compressed head, suggesting a forward binocular visual field. B. glaciale and M. punctatum larvae live deeper in the water column and had eyes elongated in the dorsal-ventral plane. The eyes of B. glaciale were prominent, projecting slightly outward from a laterally-compressed head, suggesting a strongly laterally-directed visual field. M. punctaum had stalked elongated eyes projecting from a dorso-ventrally flattened head. The eyes can be freely rotated allowing lateral, anterior and dorsally-directed vision. A prominent choroidal gland was situated beneath the ventral portion of the eye in M. punctatum and B. glaciale, while a smaller gland was present in the dorsal and ventral portions of the eye of L. crocodilus. In pre-flexion stage larvae, the retina of all three species was differentiated with numerous rod photoreceptors in the peripheral retinal areas and fewer cone photoreceptors mainly distributed in the central retina. This distribution suggests concomitant enhancement of scotopic sensitivity in the vertical visual plane and improved photopic acuity in the lateral and forward visual directions. The concurrent development of cones and rods, as observed in the pre-flexion stage of myctophid larvae, is consistent with meeting the special demands of visual planktivory in sub-surface waters. During larval development a gradual increase of ROS length was also accompanied by a progressive loss of cones that were almost totally absent in post-flexion larvae. This can be interpreted as an adaptive response to an impending deep mesopelagic adult life.

The eyes of lanternfishes (Myctophidae, Teleostei): Novel ocular specializations for vision in dim light

“…Every lanternfish species analyzed in this study possessed a pure‐rod retina. Although cone photoreceptors have been indentified in larval stages (Bozzano et al, ), our study confirmed their absence in adult myctophids. The contribution of rod outer segments to the entire retinal thickness ranged from 13% to 57% within the central part of the retina in this study.…”

Molecular ecology and adaptation of visual photopigments in craniates

“…Nevertheless, cone photoreceptors have been retained in a few species occupying the deep ocean. Examples are the lantern fish, Lampanyctus crocodilus , Benthosema glaciale and Myctophum punctatum (members of the superorder Scopelomorpha), that possess a rod‐dominated retina but retain a few cones mainly distributed in the central retina (Bozzano et al. 2007).…”

Niche partitioning and morphospace in early stages of two sympatric Diogenichthys species (Myctophidae)

“…Myctophid larvae appear to be visual predators(Conley & Hopkins, 2004) and, since their eyes are not yet fully developed and functional for nocturnal conditions(Blaxter, 1968), day-time feeding is likely more successful. According to a morphological study of the eye structure in larvae of Lampanyctus crocodilus (Risso 1810),Benthosema glaciale (Reinhardt 1837) and Myctophum punctatumRafinesque 1810, the formation of cone photoreceptors in the central area of the retina during preflexion stage indicates an increased visual capacity in daylight conditions and that these structures were progressively lost during development, as the individuals shift to adult life in deeper waters(Bozzano et al, 2007). Diogenichthys atlanticus fed more frequently during daytime and the V T peak for D. laternatus at 2200 h, which consisted almost entirely of digested remains, suggests that this species fed mostly during the afternoon.…”