Journal of Fish Biology (2011) 78, 1470–1491 doi:10.1111/j.1095-8649.2011.02954.x, available online at wileyonlinelibrary.com Morphological development of larval cobia Rachycentron canadum and the influence of dietary taurine supplementation G. Salze*†, S. R. Craig‡, B. H. Smith§, E. P. Smith‖ and E. McLean¶ *Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Duck Pond Drive, Blacksburg, VA 24061, U.S.A., ‡Virginia Cobia Farms LLC, 108 Battleground Avenue, Saltville, VA 24370, U.S.A., §Department of Physics, University of Toronto, Toronto, Ontario, Canada, ‖Department of Statistics, Virginia Tech, Blacksburg, VA 24061, U.S.A. and ¶Ministry of Fisheries Wealth, Aquaculture Centre, Al-Bustan Road, PC 100 Muscat, Sultanate of Oman (Received 30 April 2009, Accepted 15 February 2011) The morphological development of larval cobia Rachycentron canadum from 3 days post hatch (dph) until weaning (27 dph) was examined using S.E.M. Two groups of fish were studied: a con- trol group (CF), reared under standard feeding protocol, and a group in which prey items were enriched with supplemental taurine (4 g l −1 day −1 ; TF). TF fish grew faster (P< 0·001), attained greater size (mean ± s.e. 55·1 ± 1·5 v. 33·9 ± 1·0 mm total length) and had better survival (mean ± s.e. 29·3 ± 0·4 v.7·1 ± 1·2 %) than CF fish. Canonical variance analysis confirmed findings with respect to differences in growth between the treatment groups with separation being explained by two cranial measurements. S.E.M. revealed that 3 dph larvae of R. canadum (in both groups) possess preopercular spines, superficial neuromasts on the head and body, taste buds in the mouth, an olfactory epithelium which takes the form of simple concave depressions, and primordial gill arches. Gill filaments start to form as early as 6 dph and lamellae buds are visible at 8 dph in both groups. In CF fish, the cephalic lateral line system continues its development at 12–14 dph with invagination of both supra- and infraorbital canals. At the same time, a thorn-like or acan- thoid crest forms above the eye. At 14 dph, invaginations of the mandibular and preopercular canals are visible and around 22 dph enclosure of all cranial canals nears completion. In CF lar- vae, however, completely enclosed cranial canals were not observed within the course of the trial, i.e. 27 dph. In TF larvae, grooves of the cephalic lateral line system form 4 days earlier than observed in CF larvae of R. canadum (i.e. at 8 dph), with enclosure commencing at 16 dph, and completed by 27 dph. Along the flanks of 6 dph larvae of either treatment, four to five equally spaced neuromasts delineate the future position of the trunk lateral line. As myomeres are added to the growing larvae, new neuromasts appear such that at 16 dph a neuromast is associated with each myomere. By 27 dph, the trunk lateral line starts to invaginate in CF larvae, while it initi- ates closure in TF larvae. These findings elucidate important features of the larval development of R. canadum and show that dietary taurine supplementation benefits larval development, growth and survival in this species. Moreover, they suggest a conditional requirement for taurine in larval R. canadum. © 2011 The Authors Journal of Fish Biology © 2011 The Fisheries Society of the British Isles Key words: aquaculture; lateral line; neuromast; ontogeny; scanning electron microscopy; S.E.M. †Author to whom correspondence should be addressed at present address: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, N1G 2W1 Canada. Tel.: +1 519-824-4120 ext. 56688; email: gsalze@uoguelph.ca 1470 © 2011 The Authors Journal of Fish Biology © 2011 The Fisheries Society of the British Isles