Development of morphology and swimming in larvae of a coral-reef fish, the royal gramma, Gramma loreto (Grammatidae: Teleostei)

We used reared larvae of Gramma loreto sized 5.5 to 10.5 mm to study ontogeny of morphology and swimming. The larvae are slender to moderate in depth, with laterally compressed bodies, about 28 myomeres, a coiled gut that is not compact, extending to 50% to 60% of body length, an inconspicuous gas bladder, head spination limited to tiny preopercular spines, no pectoral-girdle spination, more spines than soft rays in the dorsal fin, and fins without elongate or early-forming elements. The limited pigment is most prominent along the base of the dorsal and anal fins. The development of critical speed (Ucrit) in G. loreto larvae was similar to that of other warm-water species, but speed ranged from 0.2 to 13.5 cm s^–1 (mean 7.3, SE 0.7, body lengths s^–1), which is relatively slow. Increase in speed with size was linear at 2.7 cm s^–1 per mm increase in size. The actual and relative Ucrit of G. loreto were low, and only the four largest, fastest larvae would have been swimming in an inertial hydrodynamic environment. Therefore, for most of their pelagic larval duration the ability of G. loreto larvae to influence their dispersal by horizontal swimming is likely to be low compared with that of many other warm-water fish species.