The Fish Department - Research

Behavioural Capabilities Of The Larvae Of Coral Reef Fishes

Research Scientist: Dr Jeffrey M. Leis

Larvae Of Coral Reef Fishes
In common with many marine animals, fishes that live on coral reefs have a two-part life history: a relatively sedentary adult phase on the reef, and a potentially very mobile pelagic larval phase in open water. Adult reef fishes take little or no care of their young: most larvae end up off the reef into open water where they are left to fend for themselves for anywhere from two to 20 weeks before they must find a coral reef upon which to settle. Little is known of the biology of these tiny (typically, 1-20 mm long) fishes during this pelagic period in open water. In particular, it is important to know how much control the larvae have over where they go during the pelagic phase.

Larval Fish Behaviour
Before this research project, larval fishes were generally regarded as moving passively with the currents, and having little or no control over their position or movement. We are now investigating the swimming and orientation abilities of these tiny fishes, and the results are forcing a re-think of the old view. Reef fish larvae near the end of their pelagic stage can swim at more than 20 body lengths/sec, far faster than ambient currents, and there is evidence they can detect a coral reef over 1 km away. Reef fish larvae can hear the reef, and they can smell it. They are highly aware of their surroundings, react to predators, are very particular about the bits of the reef they choose to settle upon, and frequently inspect a reef, and swim away off into open water. We now know that settlement-stage larvae are very capable and far from passive: the key question is at what point during the pelagic phase do these tiny fishes cease being at the mercy of the currents, and become the active fish we see at settlement?

Just like morphology, behaviour develops and changes during the pelagic larval phase. Australian Museum research in progress indicates that fish larvae have behaviour sufficiently well developed to have a major influence on their dispersal throughout most of their pelagic phase. Swimming speed and endurance are well-developed by the time the larvae are 4-5 mm long. Orientation ability is developed by 5-7 mm. The ability to hear is developed by at least 8 mm. Species-specific behavioural changes during the pelagic larval phase include ontogenetic ascents and descents, changes in swimming direction, and increased ability to hear.

This research is supported by the ARC, the Commonwealth Department of Industry, Science and Technology, the Hermon Slade Foundation, the Australian Museum and an international collaborative research program with French scientists ('PICS'). External collaborators include Dr Doug Cato of the Defence Science and Technology Organisation; Dr Hugh Sweatman, Australian Institute of Marine Science, Townsville; Drs René Galzin and Vincent Dufour of the Université de Perpignan, France; Dr Rebecca Fisher, James Cook University; Drs Dennis Higgs and Kirsten Poling, University of Windsor, Canada; Ms Kelly Wright and Mr Rich Piola, University of New South Wales; Mr Lou Mason, Australian Maritime College ; Dr Claire Paris, University of Miami; Dr Tom Trnski, Auckland Museum; Drs I.-S. Chen, J.-P. Chen, and L.-S. Fang, National Museum of Marine Biology, Taiwan; Dr K.-T. Shao, Academia Sinica, Taiwan. Present and former Australian Museum staff collaborators include Ms Amanda Hay, Ms Brooke Carson-Ewart, Ms Sally Reader, Ms Dianne J. Bray, Ms Domine Clark, Mr Matt Lockett, Ms Greer Howarth, and Ms Michelle Yerman.

Portions of this research project were the subject of the cover article in the 13 September 1997 issue of New Scientist (Pain. S. 1997. Swimming for Dear Life. New Scientist. 155:28-32.). Other aspects of this research were featured in the ABC-TV documentaries "Perils of Plectropomus" and the Lizard Island segment of the "Island Life" series.

View article by Bob Beale on this research project.
Marathon Fish Larvae (320k pdf) on the X-ray Mag website
Masters of Navigation (517k pdf) on the X-ray Mag website
See list of publications
See webpage on research funded by the Hermon Slade Foundation grant

Abstracts of recent papers from this research project:

Pacific coral-reef fishes: the implications of larval behaviour and ecology for biodiversity and conservation, and a reassessment of the open population paradigm.

Jeffrey M Leis
Ichthyology, Division of Vertebrate Zoology, and Centre for Biodiversity and Conservation Research, Australian Museum, 6 College Street, Sydney, NSW 2010 (Email Jeff Leis)

Synopsis:
The two-phase life history of marine fishes and invertebrates has enormous implications for dispersal, population connectivity, and resource management. Pelagic larval dispersal of marine animals is traditionally thought to ensure that populations are widespread, that chances of local extinction are low, and that marine protected areas (MPAs) can easily function to replenish both their own populations and those of unprotected areas. Traditionally, dispersal is considered to depend primarily on two variables: pelagic larval duration and far-field currents. These conclusions arise from the 'open population' paradigm and are usually accompanied by a 'simplifying assumption': larvae are distributed passively by far-field currents. Unfortunately, they ignore the complex reality of circulation and hydrological connectivity of reefs, and do not consider newly-demonstrated behavioural capabilities of coral-reef fish larvae. Far-field circulation varies with depth and often excludes water bodies where propagules are released, and this has important implications for predicting trajectories of even passive larvae. However, larvae are not passive: late-stage larvae of coral-reef fishes can swim faster than currents for long periods, can probably detect reefs at some distance, and can actively find them. This behaviour is flexible, which greatly complicates modelling of larval trajectories. Populations at ecological (as opposed to evolutionary) scales are probably less open and more subdivided than previously assumed. All this means that dispersal predictions based solely on far-field water circulation are probably wrong. An emerging view of larval fish dispersal is articulated that takes these new data and perspectives into account. This emerging view shows that re-evaluation of traditional views in several areas is required, including the contribution of larval biology and dispersal to biodiversity patterns, the way reef-fish populations are managed, and the way in which MPAs are thought to operate all require. At evolutionary and zoogeographic scales, reef-fish populations are best considered to be open.

Published in 2002, Environmental Biology of Fishes 65 (2): 199-208

Sound detection in situ by the larvae of a coral-reef damselfish (Pomacentridae)

Jeffrey M Leis¹ , Brooke M Carson-Ewart¹, Douglas H Cato²
¹Ichthyology, and Centre for Biodiversity and Conservation Research, Australian Museum, 6 College St, Sydney, NSW 2010, Australia.
Email Jeff Leis
²Defence Science and Technology Organisation PO Box 44, Pyrmont, NSW 2009, Australia

Abstract:
Settlement-stage pelagic larvae of the coral-reef damselfish Chromis atripectoralis consistently swam to the south at 24-25 cm s-1 in day-time ambient conditions off Lizard Island, Great Barrier Reef. This was true on both the windward and leeward sides of the island, 100-1000m from the nearest reef. Larvae released during the day 25-100 (mean 58) m from an underwater speaker broadcasting nocturnal reef sounds had no overall swimming direction. This was true on both windward and leeward sides of the island (500-1000m from the nearest reef). The broadcast sounds resulted in an alteration of behaviour indicating that the larvae heard them. In the presence of the nocturnal reef sounds swimming speed increased about 5 cm s-1 off the leeward side, but not the windward side. Larvae released 50-150 (mean 78) m from a speaker broadcasting artificial sound (pure tones) at the leeward location swam to the south at 30 cm s-1. This shows that larvae of C. atripectoralis can distinguish between a sound with potential biological significance and one devoid of biological significance. Larvae did not swim in any particular direction relative to the speaker when nocturnal reef sounds were broadcast: therefore, we have no evidence that the larvae can localize these sounds. We conclude that settlement-stage larvae of this damselfish can hear reef sounds, and can distinguish between reef sounds and an artificial sound, but we have no indication that they can localize the sound.

Published in 2002, Marine Ecology Progress Series 232: 259-268.

In situ settlement behaviour of damselfish larvae (Pisces: Pomacentridae)

Leis, J. M. and Carson-Ewart, B. M.
Ichthyology, and Centre for Biodiversity and Conservation Research
Australian Museum
6 College Street
Sydney, NSW 2010, Australia

Abstract:
Settlement-stage damselfish (Pomacentridae) larvae of 13 species in seven genera were obtained from light traps at Lizard Island, Great Barrier Reef, Australia. During the day, 245 larvae (6-13 mm, SL) were released individually within a few m of reefs, and their behaviour was observed in situ by SCUBA divers. Five to 60 (mean 19) individuals per species were released. Behaviour differed markedly among species. 0-28% (range among 13 species) of individuals of each species swam away from the adjacent reefs without swimming to the reefs. Of those that swam to a reef, 0-75% settled. For three species, sufficient data were available to test the hypothesis that these percentages did not differ amongst reefs: the hypothesis was rejected in one species. 0-75% of larvae that reached the reef were eaten, 0-63% subsequently left the reef, and 0-60% were still swimming over the reef at the end of the observation period. Swimming speeds of all but one species were greater when swimming away from the reef than toward it. This could constitute settlement approach by stealth. Most species exceeded average current speeds when swimming away from reefs, but not when swimming toward and over them. Average swimming depths were in the upper half of the water column for most species, and were somewhat greater where the water depths were greater. The time the larvae swam over the reef before settling and the distance swum varied greatly among species from 0 to a mean of 5.5 min and 43 m. Settlement habitats chosen differed amongst species, and in some species, they were very specific. Average settlement depth varied among species from 6 to 13.5 m. In one species, settlement depth varied between reefs. Of the 53 interactions between larvae and reef resident fishes observed, about half were predatory interactions where fishes of eight spp of six families attacked larvae. The other interactions were aggressive approaches by resident fishes, all but one of which were pomacentrids (11 species). Many of these aggressive interactions discouraged settlement attempts. Larvae of some species experienced no predatory or aggressive interactions, whereas in other species interactions averaged more than 0.6 per released larva. This seems to be related to the behaviour of the larvae, with species that swam more-or-less directly to their settlement sites experiencing more interactions. Even within the same family, settlement behaviour differs among species in nearly all measures. These observations were made during the day: settlement behaviour may differ at night.

Published in 2002, Journal of Fish Biology 61(2): 325-346

Orientation of pelagic larvae of coral-reef fishes in the ocean

Jeffrey M. Leis*, Brooke M. Carson-Ewart
Ichthyology, and Centre for Biodiversity and Conservation Research
Australian Museum, 6 College St, Sydney, NSW 2010, Australia

Abstract:
During the day, we used settlement-stage reef-fish larvae from light-traps to study in situ orientation 100-1000 m from coral reefs in water 10-40 m deep at Lizard Island, Great Barrier Reef. Seven species were observed off leeward Lizard Island, and 4 species off the windward side. All but 1 species swam faster than average ambient currents. Depending on area, time, and species, 80-100% of larvae swam directionally. Two species of butterflyfishes (Chaetodon plebeius and Chaetodon aureofasciatus) swam away from the island, indicating that they could detect the island's reefs. Swimming of 4 species of damselfishes (Chromis atripectoralis, Chrysiptera rollandi, Neopomacentrus cyanomos and Pomacentrus lepidogenys) ranged from highly directional to non-directional. Only in Neopomacentrus cyanomos did swimming direction differ between windward and leeward areas. Three species (Chromis atripectoralis, Neopomacentrus cyanomos and Pomacentrus lepidogenys) were observed in morning and late afternoon at the leeward area, and all swam in a more westerly direction in the late afternoon. In the afternoon Chromis atripectoralis larvae were highly directional in sunny conditions, but non-directional and individually more variable in cloudy conditions. All this implies damselfish larvae utilized a solar compass. Caesio cuning and Pomacentrus lepidogenys were non-directional overall, but their swimming direction differed with distance from the reef, implying the reef was detected by these species. Larvae of different species of reef fishes orientate differently and apparently use different cues for orientation while in open, pelagic waters. Current direction did not influence swimming direction. Net movement by larvae of 6 of the 7 species differed from that of currents in either direction or speed, demonstrating that larval behaviour can result in non-passive dispersal, at least near the end of the pelagic phase.

Published in 2003, Marine Ecology Progress Series 252: 239-253.

Coral-reef sounds enable nocturnal navigation by some reef-fish larvae in some places and at some times

JEFFREY M. LEIS ^*1, BROOKE M. CARSON-EWART^*, AMANDA C. HAY^* AND DOUGLAS H. CATO^#
^* Ichthyology, and Centre for Biodiversity and Conservation Research, Australian Museum, 6 College St, Sydney 2010, Australia
^# Defense Science and Technology Organisation, PO Box 44, Pyrmont 2009, Australia
¹ Author to whom correspondence should be addressed. Tel.: + 61 2 9320 6242; fax: + 61 2 9320 6059; Email Jeff Leis

Abstract:
At Lizard Island, Great Barrier Reef, catches 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 2000 and January 2001. The areas sampled in November were offshore and middle (>1000 m and 650 m offshore, respectively). In January, they were middle and near-reef (650 m and 500 m offshore, respectively). 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 offshore and middle areas. Two measures were used to evaluate the effect of sound within areas: 1) the number of nights for which each trap type had greater catches, and 2) comparison of total catches by noisy and quiet traps. At the near-reef area, noisy-trap catches of apogonid and pomacentrid larvae were significantly greater than quiet-trap catches by both measures, and noisy-trap catches of sphyraenid larvae were significantly greater by measure 2. At the middle area in January, noisy-trap catches of pomacentrid larvae were significantly greater by both measures, and those of mullids and serranids were greater by measure 2. At the middle area in November, no significant differences were found by measure 1, but noisy-trap catches of apogonids, mullids and pomacentrids were significantly greater by measure 2. Increases in catch by noisy traps at the near-reef and middle area were 19-105% for pomacentrids, and 38-155% for apogonids. At the near-reef and middle areas, catches of no taxa were significantly greater in quiet traps by either measure. In the offshore area, by measure 1 no significant differences in catch were found, but, by measure 2, significantly greater catches were found in quiet traps for apogonids, blenniids, chaetodontids, mullids and pomacentrids, and in noisy traps for lethrinids. Thus, some taxa (particularly apogonids and pomacentrids, but also lethrinids and mullids), 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 over frequencies typical of fish hearing were equivalent to background levels, providing a maximum radius of sound attraction in this experiment.

Published in 2003 Journal of Fish Biology 63, 724-737

Vertical distribution behaviour and its spatial variation in late-stage larvae of coral-reef fishes during the day

Jeffrey M Leis

ABSTRACT
Daytime vertical distribution behaviour of settlement-stage reef-fish larvae in the upper 18 m was documented by diver observations of 497 pelagic larvae of 7 species 100-1000 m offshore of Lizard Island, Great Barrier Reef. Four species were studied on 2 sides of the island. Depth amplitude and depth-frequency differed among species, locations and times. Four pomacentrids had modal depths in the upper 30-50% of the water column. A lutjanid and 2 chaetodontids had modal depths 0-2 m deeper than the deepest-swimming pomacentrid. On the leeward side, 6 of 7 species swam deeper and/or more variably offshore. On the windward side, 1 of 4 species swam deeper or more variably offshore. No larvae swam deeper than 18 m on the leeward side, but 31% of larvae of 3 species did so on the windward side. Three of 4 species swam deeper and/or more variably on the windward than leeward side. Vertical distributions in relatively shallow water are apparently strongly influenced by water-column depth and bottom type.

Published 2004, Marine and Freshwater Behaviour and Physiology,. 37(2): 65-88

Localization of reef sounds by settlement-stage larvae of coral-reef fishes (Pomacentridae).

Jeffrey M Leis¹ and Matthew M Lockett^1,2
¹ Ichthyology and Division of Aquatic Zoology, Australian Museum, 6 College St, Sydney, NSW 2010, Australia
² Department of Environmental Sciences, University of Technology, Westbourne Street, Gore Hill, NSW 2065, Australia

ABSTRACT
Settlement-stage larvae of five pomacentrid species were tested for the ability to hear and localize reef sounds in a nocturnal field experiment at Lizard Island, Great Barrier Reef. Linear selection chambers allowed larvae to swim either toward or away from nocturnal reef sounds from an underwater speaker 25 m away. Data were analyzed under two assumptions: 1) that each individual larva in a selection chamber acted independently, and 2) that they did not act independently. Two-thirds of Chromis atripectoralis larvae swam toward the reef sound, and this tendency was significant regardless of the assumption of independence. Larvae of C. atripectoralis were also more likely to swim toward the speaker when it was broadcasting sound than when it was quiet. Neopomacentrus cyanomos larvae also swam toward the sound, but this was statistically significant only under assumption 1. Three Pomacentrus species did not swim toward the sound, although under assumption 1, one was significantly more likely to swim away from it. These results seem to show among-species differences in the response to sound, but the possibility of temporal differences in behavior cannot be ruled out. Larvae of at least some pomacentrid species can use reef sounds to localize a sound source at night, providing evidence that sound emanating from reefs at night is a useable sensory cue for fish larvae trying to find settlement habitat.

Bulletin of Marine Science, 76(3): 715–724, 2005

Feeding greatly enhances endurance swimming of settlement-stage reef-fish larvae (Pomacentridae)

Jeffrey M Leis and Domine Clark
Ichthyology, and Division of Aquatic Zoology,
Australian Museum,
6 College St,
Sydney, NSW 2010,
Australia

ABSTRACT
Previous measures of the swimming endurance abilities of late-stage larvae of reef fishes have used laboratory swimming chambers, and with one exception, unfed larvae. Based on the exceptional study, we predicted that fed larvae should have much greater endurance than previously reported for unfed larvae. We tested the swimming endurance of the fed late-stage larvae of six pomacentrid species, and found that all could swim at least twice as long as unfed larvae. The three species with larger larvae (12-14 mm SL) all grew during these experiments in spite of being forced to swim 23.3 hr per day. The three species with smaller larvae (10-11 mm SL) did not show consistent growth. Unfed laboratory measures of swimming endurance are, therefore, very conservative, and are probably more of an indication of the reserves available to the larvae than a realistic indication of how far the larvae are capable of swimming in the field.

Ichthyological Research (2005) 52: 185–188

Ontogeny of swimming abilities of the larvae of four temperate marine fishes

Domine L Clark, Jeffrey M Leis^*, Amanda C Hay and Thomas Trnski
Ichthyology, Division of Aquatic Science, Australian Museum, 6 College Street, Sydney, NSW 2010, Australia. ^* author for correspondence: Email Jeff Leis

ABSTRACT
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 we measured the development of critical speed and endurance swimming in reared larvae of four 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 two 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, it performance 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 15-20 cm s-1 (=12-20 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 corresponds 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.

Marine Ecology Progress Series Vol. 292: 287–300, 2005

Swimming speed of settlement-stage reef-fish larvae measured in the laboratory and in the field: a comparison of critical speed and in situ speed

Jeffrey M LEIS¹ and Rebecca FISHER²
¹ Ichthyology, Australian Museum, 6 College Street, Sydney, NSW 2010, Australia
² Santa Cruz Laboratories, National Marine Fisheries Service, 110 Shaffer Road, Santa Cruz, California, 95060, USA. Present address: Department of Biology, University of Windsor, Windsor, Ontario, Canada N9B3P4

ABSTRACT
Knowledge of swimming abilities of pelagic larval fishes is important for understanding dispersal and connectivity in reef-fish populations, and is needed to model dispersal realistically. Two measures of swimming speed - critical speed (Ucrit) and in situ speed - confirm that larvae of many species swim fast. Ucrit is determined using laboratory swimming flumes, and increasing speed incrementally until the larva can not maintain position. Ucrit measures maximum swimming speed and is ideal for comparisons among species and developmental stages. However, it is a measure of potential performance, and its relationship to actual swimming speeds in the field remains unclear. In situ speed is chosen by the larva in the field, and is measured by SCUBA divers following the larva. In situ speed is difficult and labor-intensive to measure, but it is the only available method for measuring swimming speed of fish larvae in the ocean. Using settlement-stage larvae from light traps, we compared Ucrit to in situ speed for 11 families of coral-reef fishes: Acanthuridae, Apogonidae, Chaetodontidae, Holocentridae, Lethrinidae, Lutjanidae, Nemipteridae, Pomacanthidae, Pomacentridae, Serranidae and Tetraodontidae. The overall means of in situ speed and Ucrit were 20 cm s-1 and 36 cm s-1, respectively. For both measures on average, within a species, the fastest individual was 50% faster than the mean speed. Ucrit and in situ speed were significantly correlated. For both mean and maximum values at both species and family level, in situ speed averaged 50% of U-crit. This relationship can be used to estimate swimming speed of late-stage larvae in the ocean from a convenient laboratory measure.
2006 P 438-445. In:Y. Suzuki, T Nakamori, M. Hidaka, H. Kayanne, B.E. Casareto, K. Nadaoka, H. Yamano and M. Tsuchiya (eds), Proceedings of the 10th International Coral Reef Symposium, Okinawa. The Japanese Coral Reef Society, University of Tokyo, Tokyo.

In situ ontogeny of behaviour in pelagic larvae of three temperate, marine, demersal fishes

Jeffrey M. Leis, Amanda C. Hay and Thomas Trnski
Ichthyology, Australian Museum, 6 College St, Sydney, NSW, 2010, Australia
¹ -author for correspondence: ph, 61 9320 6242; fax, 61 9320 6059, (Email Jeff Leis)

ABSTRACT
The ontogeny of behaviour relevant to dispersal was studied in situ with reared pelagic larvae of three warm-temperate marine, demersal fishes: Argyrosomus japonicus (Sciaenidae), Acanthopagrus australis and Pagrus auratus (both Sparidae). Larvae of 5-14 mm SL were released in the sea, and their swimming speed, depth and direction were observed by divers. Behaviour differed among species, and to some extent, among locations. Swimming speed increased linearly at 0.4-2.0 cm s -1 per mm size, depending on species. The sciaenid was slower than the sparids by 2-6 cm s -1 at any size, but uniquely, it swam faster in a sheltered bay than in the ocean. Mean speeds were 4-10 body lengths s -1. At settlement size, mean speed was 5-10 cm s -1, and the best performing individuals swam up to twice the mean speed. In situ swimming speed was linearly correlated (R 2=0.72) with a laboratory measure of swimming speed (critical speed): the slope of the relationship was 0.32, but due to a non-zero intercept, overall, in situ speed was 25% of critical speed. Ontogenetic vertical migrations of several metres were found in all three species: the sciaenid and one sparid descended, whereas the other sparid ascended to the surface. Overall, 74-84% of individual larvae swam in a non-random way, and the frequency of directional individuals did not change ontogenetically. Indications of ontogenetic change in orientated swimming (ie, the direction of non-random swimming) were found in all three species, with orientated swimming developed in the sparids by about 8 mm. One sparid swam W (toward shore) when <10mm, and changed direction toward NE (parallel to shore) when >10mm. These results are consistent with limited in situ observations of settlement-stage wild larvae of the two sparids. In situ, larvae of these three species have swimming, depth determination, and orientation behaviour sufficiently well developed to substantially influence dispersal trajectories for most of their pelagic period.

2006 Marine Biology 148 (3): 655-669

Behavioral ontogeny in larvae and early juveniles of the Giant Trevally, Caranx ignobilis (Pisces: Carangidae)

Jeffrey M. Leis¹, Amanda C. Hay¹, Domine L. Clark¹, I-Shiung Chen² and Kwang-Tsao Shao³
¹Ichthyology, Aquatic Zoology, Australian Museum, 6 College Street, Sydney, NSW 2010, Australia (ph 61 2 9320 6242; fax 61 2 9320 6059; (Email Jeff Leis)

² National Museum of Marine Biology & Aquarium, 2 Houwan Road, Checheng, Pingtung, 944, Taiwan
present address: Institute of Marine Biology, National Taiwan Ocean University, 2 Pei Ning Road, Keelung, 20224 Taiwan

³ Institute of Zoology, Academia Sinica, Academia Road, Nankang, Taipei, 115, Taiwan

Keywords : Larvae, behavior, Carangidae, ontogeny, swimming speed, orientation, vertical distribution, dispersal

ABSTRACT
Larvae and juveniles (8-18 mm SL) of Caranx ignobilis, a large pelagic predatory fish associated with coral reefs, were obtained from a commercial aquaculture farm, and their behavior was observed in both laboratory swimming chambers and in the ocean. For swimming speed and endurance, size was a better predictor of performance than was age. Critical speed, a laboratory measure, increased with size from 12 to 40 cm s-1 at about 2.7 cm s-1 per mm of growth. Mean scaled critical speed was 19 body lengths per second, and was not related to size. Swimming speed in the ocean (in situ speed) was 4 to 20 cm s-1 and varied among the four study areas, but within each area, it increased with size at about 2 cm s-1 per mm growth. In situ speed was about half of critical speed. Swimming endurance in the laboratory (unfed) increased with size from about 5 to 40 km at about 5 km per mm of growth. Vertical distribution behavior in the ocean changed ontogenetically, with larvae swimming somewhat shallower, but more variably, and then much deeper with growth. Two-thirds of individuals swam directionally in the ocean, but there was no indication of an ontogenetic increase in precision of orientation. Larvae swam offshore (westerly) at an open coast location, but had no overall swimming direction at another location in a bay. Unplanned in situ observations of C. ignobilis feeding, interacting with pelagic animals and reacting to coral reefs are also reported.

2006 US Fishery Bulletin 104(3):401-414

Auditory and olfactory abilities of pre-settlement larvae and post-settlement juveniles of a coral reef damselfish (Pisces: Pomacentridae)

K. J. Wright, D. M. Higgs, A. J. Belanger and J. M. Leis

ABSTRACT
The propagules of most species of reef fish are advected from the reef, necessitating a return to reef habitats at the end of the pelagic stage. There is increasing evidence of active attraction to the reef but the sensory abilities of reef fish larvae have not been characterized well enough to fully identify cues. The electrophysiological methods of auditory brainstem response (ABR) and electroolfactogram (EOG) were used to investigate auditory and olfactory abilities of pre- and post-settlement stages of a damselfish, Pomacentrus nagasakiensis (Pisces, Pomacentridae). Audiograms of the two ontogenetic stages were similar. Pre-settlement larvae heard as well as their post-settlement counterparts at all but two of the tested frequencies between 100 Hz and 2,000 Hz. At 100 and 600 Hz, pre-settlement larvae had ABR thresholds 8 dB higher than those of post-settlement juveniles. Both stages were able to detect locally recorded reef sounds. Similarly, no difference in olfactory ability was found between the two ontogenetic stages. Both stages showed olfactory responses to conspecifics as well as L-alanine. Therefore, the auditory and olfactory senses have similar capabilities in both ontogenetic stages. Settlement stage larvae of P. nagasakiensis can hear and smell reef cues but it is unclear as to what extent larvae use these sounds or smells, or both, as cues for locating settlement sites.

2005 Marine Biology 147: 1425-1434.

Critical swimming speeds of late-stage coral reef fish larvae: variation within species, among species and between locations

Rebecca Fisher Jeffrey M. Leis Domine L. Clark and Shaun K. Wilson

ABSTRACT
The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators, obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean. Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition factor of these same larvae. Among species U-crit ranged from 5.5 cm s_1 to 100.8 cm s_1 (mean=37.3 cm s_1), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat use following settlement.

2005 Marine Biology 147: 1201-1212

Reviews of this research on behavioural capabilities can be found in: Leis, J. M. and M.I. McCormick. 2002. The biology, behaviour and ecology of the pelagic, larval stage of coral-reef fishes. P171-199 In P.F. Sale, (ed). Coral Reef Fishes: Dynamics and diversity in a complex ecosystem. Academic Press, San Diego; and Leis, J.M. 2006. Are larvae of demersal fishes plankton or nekton? Advances in Marine Biology 51: 57-141 .

Dr Leis Page