Morphological and swimming ontogeny in larvae of a small predator on coral reefs: the orchid dottyback (Pseudochromis fridmani) (Teleostei, Pseudochromidae)

Dottybacks (family Pseudochromidae) are small, colorful, important predators on juvenile fishes on Indo-Pacific coral reefs. Most aspects of their larval ontogeny are little studied. Reared larvae of the orchid dottyback (Pseudochromis fridmani) of 4 to 12 mm body length (BL) were used to document both morphological and swimming ontogeny in 3 cohorts. Development is direct. Larvae are slender, lightly pigmented, lack obvious specializations to pelagic existence, and settle at about 12 mm BL. This morphology is similar to that of several families of tropical waters including silliganids, scarids, some labrids, and plesiopids. Critical swimming speed (Ucrit) was measured in 85 larvae, which swam at 0.2 to 19 cm/s. In an unplanned comparison, larvae reached greater Ucrit values at 28°C than at 26°C. Only larvae of ≥9 mm BL could swim fast enough to reach an inertial hydrodynamic environment, wherein swimming is likely to be sustainable enough to influence dispersal. However, 60% of larvae of ≥9 mm were unable to do so, and half of these swam in a viscous environment dominated by frictional drag. Results from this study will allow Pseudochromis larvae from field sampling to be identified, may assist studies of pseudochromid relationships, and will help determine the extent to which horizontal swimming of Pseudochromis larvae may influence dispersal and population connectivity and be influenced by temperature.