Development of the vertebral column, fins and fin supports in the Japanese anchovy, Engraulis japonicus (Clupeiformes: Engraulididae)
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The ontogeny of the median and paired fins and their supports, the vertebral column, predorsal bones, and pleural ribs of Engraulis japonicus are described. A size series of 101 laboratory-reared specimens 2.3 mm NL to 37.3 mm SL from 0 to 59 days old, and an additional series of 181 wild-caught anchovy 1.5 mm NL to 1 10.6 mm SL were cleared and stained for both cartilage and bone. All fin supports form from cartilage in the following sequence: pectoral, caudal, dorsal, anal, and pelvic fin support. Completion of fins is in a different order. Almost all fin structures are present and partially ossified by the 51st day after hatching (ca. 2427 mm SL). Caudal fin supports start development in 6.1 mm NL 9 day old larvae with chondrification of hypural 1 below the unflexed notochord. The anterior adult epural develops from two pieces of cartilage. Caudal fin rays develop from middle ones outward. Full complement of principal caudal rays is present in larvae 78.0 mm SL (11-20 days after hatching). Dorsal and anal fin anlagens appear in larvae 76.2 mm SL. The enlarged first dorsal proximal radial originates from one piece of cartilage. A supernumerary dorsal distal radial develops behind the first distal radial. Left and right coraco-scapula cartilages appear first fused ventromedially. Propterygium develops from the pectoral radial plate. The pelvic scute originals from three scale-like pieces accounting for the lateral arms and the basal plate. Ossification of centra begins from 12.2 mm SL. Neural and haemal arches begin chondrification by 7.3 mm SL. Twelve or 11 predorsal bones start to chondrify posteriad by 15.8 mm SL in larvae 21 days old. Twenty four pairs of pleural ribs develop partially of cartilage and dermal origin. Comparisons with other clupeiform species stress the necessity of further research in this fish group