Prerequisites for understanding dispersal in pelagic larvae of demersal fishes are data on when swimming abilities of larvae are sufficiently developed to be able to alter passive dispersal trajectories. In laboratory swimming chambers, the development of critical speed and endurance swimming was measured in reared larvae of 4 species of warm-temperate marine and estuarine fishes that spawn pelagic eggs (Sciaenidae, Argyrosomus japonicus; Sparidae, Pagrus auratus, Acanthopagrus australis; Percichthyidae, Macquaria novemaculeata). Size was a better predictor of swimming ability than age. Increase in critical speed with growth was best portrayed by linear or 'flat' curvilinear relationships. Increase in endurance was best portrayed by strongly concave curvilinear relationships. The percichthyid larvae had the highest critical speed initially, but speed increased slowly with growth. The 2 sparids had the greatest increase in speed with growth, and the sciaenid the least. The greatest increase in endurance with growth was found in P. auratus, but performance of M. novemaculeata was only slightly less. The slowest increase in endurance with growth was found in A. japonicus, but, by settlement, its performance was similar to the other species. Until notochord flexion was complete, both speed and endurance were limited. Thereafter, swimming performance improved markedly at a species-specific rate. At settlement, larvae of these species could swim more than 10 km and at speeds of 15 to 20 cm s -1 (=12 to 20 BL s -1 ), which exceeded the average currents in their coastal environment. Following notochord flexion, all larvae swimming at critical speed were in an inertial environment, and this corresponded to when substantial endurance swimming developed. Whether these potential performances are actually realized in the field remains to be determined, but they provide the potential to strongly influence dispersal.KEY WORDS: Dispersal · Ontogeny · Swimming · Larvae · Critical speed · Endurance · Fish · Sparidae · Sciaenidae · PercichthyidaeResale or republication not permitted without written consent of the publisher

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Behaviour during the pelagic larval stage of coral-reef fishes can strongly influence dispersal, yet little is known of behavioural ontogeny. Speed, orientation and vertical distribution of larvae of 4 coral-reef fishes ( ) across the size range. All but the smallest, slowest larvae had Reynolds numbers >1000, and so swam in an inertial environment. In situ speeds were 39 to 87% of critical speeds, and smaller larvae swam nearer to critical speed than larger larvae. Of the larvae 71 to 90% swam directionally, but neither percentage of directional individuals nor orientation precision increased with size. P. teira swam toward the southwest (offshore). Epinephelus species undertook ontogenetic changes in orientation. Neither orientation nor ontogenetic changes were found in L. malabaricus. Horizontal swimming can influence dispersal directly. Vertical distribution, which differed among species, can influence dispersal indirectly. P. teira became surface orientated, ascending 0.8 m per mm increase in length. L. malabaricus descended 0.5 m per mm increase in length. E. coioides ascended 0.4 m per mm increase in length. E. fuscoguttatus preferred greater depths, and lacked ontogenetic changes. The behaviours and their development show these larval reef fishes can influence dispersal in speciesspecific ways.KEY WORDS: Connectivity · Dispersal · Larva · Ontogeny · Development · Coral reef · Fish · Serranidae · Lutjanidae · EphippidaeResale or republication not permitted without written consent of the publisher

At Lizard Island, Great Barrier Reef, catches of fish larvae by light traps that broadcast nocturnal reef sounds (noisy traps) were compared with catches by quiet traps over two 2·5 week new‐moon periods in November (XI) 2000 and January (I) 2001. Three areas were sampled: near‐reef (NR, 500 m from the shore) in I, middle (M, 650 m) in I and XI and offshore (O, >1000 m) in XI. The most abundant taxa captured were Apogonidae, Blenniidae, Chaetodontidae, Lethrinidae, Mullidae and Pomacentridae. Significant differences in catch were found between areas, and a position effect was found at the O and M areas. At the NR and M areas, no taxa had significantly greater catches in quiet traps, but larvae of five taxa had significantly greater catches in noisy traps. These were (areas and times of greater catches): Apogonidae (NR; M XI), Mullidae (M I & XI), Pomacentridae (NR; M I & XI), Serranidae (M I) and Sphyraenidae (NR). At the offshore area, five taxa (Apogonidae, Blenniidae, Chaetodontidae, Mullidae and Pomacentridae) had significantly greater catches in quiet traps and only Lethrinidae had significantly greater catches in noisy traps. Thus some taxa (particularly apogonids and pomacentrids which had catches up to 155% greater in noisy traps, but also lethrinids and mullids, and perhaps others), were attracted to reef sounds at night, but this apparently varied with location and time. The sound‐enhanced catches imply a radius of attraction of the sound 1·02–1·6 times that of the light. More than 65 m from the speaker,the broadcast sound levels at frequencies typical of fish hearing were equivalent to background levels, providing a maximum radius of sound attraction in this experiment.

During the pelagic larval phase of teleost fishes, the larvae are subject to dispersal by currents. Dispersal trajectories can be substantially modified if the larvae have sufficient swimming abilities, so it is important to document how swimming ability develops during the pelagic larval phase. We used reared larvae (4 to 29 mm standard length) from commercial aquaculture farms in Taiwan to measure the development of swimming ability (critical speed, U crit) in larvae of 9 species (from 7 families) of Indo-Pacific coral reef and coastal fishes that hatch from pelagic eggs: Trachinotus blochii (Carangidae-jacks), Chanos chanos (Chanidae-milkfish), Platax teira (Ephippidaebatfishes), Leiognathus equulus (Leiognathidae-ponyfishes), Lutjanus malabaricus (Lutjanidaesnappers), Eleutheronema tetradactylum (Polynemidae-threadfins), and Epinephelus coioides, E. fuscoguttatus and E. malabaricus (Serranidae-groupers). Mean critical swimming speeds increased from < 5 cm s-1 in the smallest larvae to a maximum of 47 cm s-1 in settlement stage larvae, with the increase in speed by the time of settlement ranging from 6-to 100-fold. Increase in swimming speed was more strongly correlated with size of larvae (R 2 = 0.38 to 0.93, p < 0.005) than with age (correlation with age was absent in 3 species and explained 10 to 43% less variation than did size in the others). The relationship between speed and size was linear. In 6 species (T. blochii, C. chanos, L. malabaricus and the 3 Epinephelus species) speed increased at a rate of 2.1 to 2.6 cm s-1 for each 1 mm increase in size. Three species (P. teira, L. equulus and E. tetradactylum) had a significantly slower rate of increase of 1.3 to 1.7 cm s-1 for each 1 mm increase in size. On average, the best performers in each 1 mm size increment were 1.5 to 7.3 cm s-1 faster than mean performers, depending on species. Throughout development the vast majority of mean length-specific speeds were 10 to 20 body lengths (BL) s-1 , and length-specific speed increased significantly with size in 6 species. Maximum length-specific speeds for each species reached 18 to 31 BL s-1. Although the ontogeny of swimming speed varies among species of tropical marine fishes, over similar size ranges, larvae that hatch from pelagic eggs have swimming abilities similar to those reported for larvae that hatch from demersal eggs.