Diagnostic characters: Small fishes, from 2-30 cm as adults. Body typically elongate; head large with jaws reaching posterior margin of eye and beyond; eye large. Small teeth in bands on the premaxillaries and dentaries, sometimes flattened but seldom enlarged. Gill rakers well developed but absent in Centrobranchus nigroocellatus, Roundnose Lanternfish. Dorsal-fin base at midbody, fin sometimes relatively high; posterior dorsal-fin base nearly above or behind anal-fin origin; 10-26 soft rays. Dorsal adipose fin present. Anal fin under or just behind base of dorsal fin;12-27 soft rays. Principal caudal-fin rays 10 + 9 = 19.Pectoral fins rudimentary to very long; 10-18 soft rays. Pelvic fins under or just before anterior base of dorsal fin; pelvic-fin soft rays usually 8 but 6 in Notolychnus valdiviae, Topside Lanternfish, and sometimes 7 in Gonichthys cocco, Linestop Lanternfish. Scales deciduous. Photophores present in groups on head and body. Additional luminous tissue may be found on head, scales, fins, and as glands on the upper and/or lower caudal peduncle. Color: mainly brown to black in deeper water species, silvery in shallower water species; often with metallic blue or green scales (FAO 2002).
Identification based primarily on arrangement of various photophore groups named in figure. Photophores often damaged in nets, but remnants and/or scars usually identifiable with microscope. Gill-raker counts (on 1st gill-arch) include only movable, developed elements, not small anterior knobs on upper and lower gill arch, some of which may be movable. Luminous tissue other than body photophores and head-light organs have usually been termed luminous scales in previous works. As they are not true fish scales, they are termed ‘scale-like plates’ (if well defined as in SCO) and ‘scale-like patches’ (without firm, distinct borders), often shortened to plates or patches (FAO 2020).
References:
(FAO. 2002). The living marine resources of the Western Central Atlantic. Volumes 1-3. K.E. Carpenter (ed.). Food and Agriculture Organization of the United Nations, Rome, Italy. 4099p. (Available at: http://www.fao.org/3/y4160e/y4160e00.htm).
(FAO 2020) Sutton, T.T., P.A. Hulley, R. Wienerroither, D. Zaera-Perez, and J.R. Paxton. 2020. Identification guide to the mesopelagic fishes of the central and south east Atlantic Ocean. FAO Species Identification Guide for Fishery Purposes. Rome, FAO. 2020. https://doi.org/10.4060/cb0365en.