Unlike the mammalian retina, the teleost fish retina undergoes persistent neurogenesis from intrinsic stem cells. In marine teleosts, most cone photoreceptor genesis occurs early in the embryonic and larval stages, and rods are added primarily during and after metamorphosis. This study demonstrates a developmental paradigm in elopomorph fishes in which retinas are rod-dominated in larvae, but undergo periods of later cone genesis. Retinal characteristics were compared at different developmental stages among three ecologically distinct elopomorph fishes—ladyfish (Elops saurus), bonefish (Albula vulpes), and speckled worm eel (Myrophis punctatus). The objectives were to improve our understanding of (1) the developmental strategy in the elopomorph retina, (2) the functional architecture of the retina as it relates to ecology, and (3) how the light environment influences photoreceptor genesis. Photoreceptor morphologies, distributions, and spectral absorption were studied at larval, juvenile, and adult stages. Premetamorphic retinas in all three species are rod-dominated, but the retinas of these species undergo dramatic change over the course of development, resulting in juvenile and adult retinal characteristics that correlate closely with ecology. Adult E. saurus has high rod densities, grouped photoreceptors, a reflective tapetum, and longer-wavelength photopigments, supporting vision in turbid, low-light conditions. Adult A. vulpes has high cone densities, low rod densities, and shorter-wavelength photopigments, supporting diurnal vision in shallow, clear water. M. punctatus loses cones during metamorphosis, develops new cones after settlement, and maintains high rod but low cone densities, supporting primarily nocturnal vision. M. punctatus secondary cone genesis occurs rapidly throughout the retina, suggesting a novel mechanism of vertebrate photoreceptor genesis. Finally, in postsettlement M. punctatus, the continuous presence or absence of visible light modulates rod distribution but does not affect secondary cone genesis, suggesting some degree of developmental plasticity influenced by the light environment.

This is the first record of a ladyfish (Elops smithi) larva in Uruguay and the southernmost South Atlantic record. We provide morphological–merisitc and environmental information about the larva collected in March 2010 in brackish waters of the Solís Grande estuary. The sampling site was 0.9 m depth, water was warm (21.7 °C), low salinity (12.3) and with high oxygen content (7.7 mg l−1). The larva was very transparent, 31 mm in standard length and had a total of 76 myomeres. The dorsal fin (24 rays) and the anal fin (16 rays) did not overlap. The caudal fin was forked; the pectoral fin without rays and pelvic fin was in an early phase. The swim bladder was inverted U shaped. The half premaxilla had 8 teeth and the half mandible 10 (of similar size and appearance). Pigments were present in the ventral line (from the thorax to anus) and in the middle lateral trunk and caudal peduncle line. These characteristics suggested an early-metamorphic stage of the larva. This species is recorded with low abundances in southern Brazil. The collection of this individual occurred during a period of strong El Niño (2009–2010). These events are associated with warm sea surface temperature anomalies in the south-western Atlantic and northerly winds anomalies in the Brazilian–Uruguayan continental shelf.