Taxonomy and Systematics of Larval Indo-Pacific Fishes
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Ichthyol Res DOI 10.1007/s10228-014-0426-7 REVIEW FOR IPFC9 SPECIAL ISSUE Ichthyology and Indo-Pacific Fish Conferences from the 1980s to the 2010s Taxonomy and systematics of larval Indo-Pacific fishes: a review of progress since 1981 Jeffrey M. Leis Received: 2 May 2014 / Revised: 24 June 2014 / Accepted: 8 July 2014 Ó The Author(s) 2014. This article is published with open access at Springerlink.com Abstract This paper reviews progress in research on ontogeny to contribute to the study of phylogeny of marine taxonomy and systematics of larval marine and estuarine fishes has been underrealized. The ageing of current larval- fishes in the Indo-Pacific since the first Indo-Pacific Fish fish taxonomists, and the lack of positions for younger Conference in 1981. In 1981, the literature on development replacement researchers, is a major obstacle to further of fish larvae in the vast Indo-Pacific region was sparse, progress. scattered and of very uneven quality. During the inter- vening 33 years, taxonomy of adult Indo-Pacific fishes has Keywords Ontogeny Á Development Á Teleostei Á Larva Á improved greatly, the proceedings of the landmark Ahl- Identification strom Symposium were published, a large number of lar- val-fish atlases, or identification guides, have been produced, and the quality of descriptions of larval-fish Introduction development in journals has greatly increased. This has resulted in a great improvement in our ability to identify The vast majority of marine teleost fishes—regardless of Indo-Pacific fish larvae, particularly oceanic taxa. How- their adult habitat—have a pelagic larval phase that differs ever, much remains to be done, with the large majority of greatly in morphology from the adult. The larvae of epi- families having \50 % of species with described larvae, pelagic species share the same habitat with their adults. In and with only a small proportion of species descriptions contrast, larvae of meso- and bathypelagic species are based on full developmental series of larvae. DNA tech- typically found in the epipelagic zone, much closer to the nology has helped to establish identities of larvae, but only surface than their adults, and undergo an ontogenetic des- a small proportion of the larvae so identified have been cent as they grow and develop (e.g. Loeb 1979). In described, so the potential for DNA to advance larval demersal species, only a handful of taxa are known to have taxonomy is largely untapped. An integrative approach larvae that are not epipelagic, so the adults and larvae of combining genetics and morphology is required. Online most species occupy very different habitats: the larvae are publication of descriptions of larval development and of in open water and faced with the challenge of finding interactive identification guides to larvae is the most effi- appropriate demersal settlement habitat at the end of their cient way to make such information available and useful to pelagic phase. Typically, large morphological changes are a variety of users. The great potential for larval-fish associated with the transition between pelagic and demer- sal phases, although in several major clades (e.g. Tetra- odontiformes), there is an extended pelagic phase that J. M. Leis (&) Institute for Marine and Antarctic Studies, University of differs little morphologically from the adult. Attempts to Tasmania, Hobart, Tasmania 7007, Australia develop clear, widely used terminology to describe these e-mail: [email protected] morphological and ecological ontogenetic changes and transitions have failed, largely due to wide variability J. M. Leis Ichthyology, Australian Museum, Sydney, among taxa in mode of development or ecology (Kendall New South Wales 2010, Australia et al. 1984). For the purposes of this paper, I will include 123 J. M. Leis all of the post-hatching, but pre-settlement stages of description of the serranid genus Flagelloserranus by demersal species (i.e. the pelagic phase, an ecological Kotthaus (1970), but within a year, Flagelloserranus was criterion). It is common to declare the larval stage of identified by Fourmanoir (1971) as the pelagic larval form pelagic species to end at a somewhat arbitrarily chosen of the serranid genus Liopropoma. In some cases, these morphological milestone, for example, the attainment of generic names have been retained to describe the mor- full fin-ray counts, or the presence of scales. But, I would phology of the pelagic larval stage (e.g. leptocephalus, prefer to be a bit flexible with pelagic species, so some of rhynchichthys, dikellorhynchus, tholichthys, acronurus, the more spectacular larval morphologies can be included. Fig. 2). The large morphological differences between lar- Larvae frequently bear little resemblance to the adults val and adult stages make identification of the larvae for two reasons: 1) the larvae are, at least initially, challenging, and the larvae of many species and higher taxa incompletely developed and lack structures found in adults remain undescribed. (e.g. scales or fins), and 2) the larvae frequently have A particular challenge for those who want to identify specializations to pelagic existence that result in some of larval fishes results from collection methods. Many studies the most spectacular marine creatures known (Fig 1.), but rely on towed nets or other relatively unselective methods these specializations are lost as development proceeds. Due to capture fish larvae. This means that larvae of species that to the great morphological differences between the adult live in a very wide variety of habitats as adults are captured and larval stages of many taxa, during the 19th and much in the same sample—thus, the researcher who wants, for of the 20th centuries, the larvae of a number of Indo-Pacific example, to study larvae of coral-reef fishes will encounter, fishes were described as distinct species, or even genera and must also be able to identify at least to family, larvae (e.g. holocentrids, acanthurids, malacanthids, many eels). from oceanic and coastal, pelagic habitats, from deep, The last example of this sort of confusion was the offshore waters, from soft bottoms on the continental shelf Fig. 1 Morphological diversity in larvae of Indo-Pacific fishes. ca 12 mm; c Serranidae, Epinephelinae, Diploprion bifasciatum,ca Photos by Frank Baensch—http://www.bluereefphoto.org (unless 22 mm; d Lethrinidae, Monotaxis grandoculis, 6.7 mm; e Chae- noted otherwise, all are reared from pelagic eggs taken in Hawaiian todontidae, Forcipiger flavissimus, 8.3 mm; f Acanthuridae, Zebra- waters), except c and f by Colin Wen (Great Barrier Reef, night light). soma veliferum, ca 26 mm; g Bothidae, Asterorhombus or Sizes are total length. a Serranidae, Anthiinae, Odontanthias fuci- Engyprosopon, 34.2 mm. Papua New Guinea, night light; h Molidae, pinnis, 20.3 mm; b Serranidae, Epinephelinae, Cephalopholis argus, Ranzania laevis, 5.1 mm 123 Taxonomy of Indo-Pacific fish larvae Fig. 2 Specialized larval stages originally described as new genera leptocephalus stage, 15.0 mm; b Holocentridae, Myripristis sp, and the common names for their morphology derived from the rhynchichthys stage, 13.4 mm, Papua New Guinea, night light; generic name. Photos by Frank Baensch—http://www.bluereefphoto. c Malacanthidae, Malacanthus brevirostris, dikellorhynchus stage, org. All are reared from pelagic eggs taken in Hawaiian waters, 18.3 mm; d Chaetodontidae, Chaetodon sp, tholichthys stage, except for b. Sizes are total length. a Anguilliformes, unidentified eel, 6.6 mm; e Acanthuridae, Acanthurus sp, acronurus stage, 6.9 mm and, in many cases, from estuaries and even freshwater. As light on the relationships and evolution of a broad range of a result, the larval-fish researcher must be familiar with a fish taxa. Unfortunately, the number of such researchers is much wider variety of fishes than the typical researcher small relative to the task and, in spite of the potential of who works on adult fishes. Among researchers who work this research approach, is not growing fast and may well be on fishes—including taxonomists—the common perception decreasing. is that larval-fish biology is a separate discipline, and there In 1981, the literature on Indo-Pacific larval-fish are relatively few researchers who have either the incli- development and identification was scattered, uneven in nation or the ability to identify both adult and larval fishes. quality, often in obscure journals or expedition reports, and This perception has limited the development of larval-fish frequently in languages that rendered much of the content biology. inaccessible to many potential users. Larvae of many This paper is an assessment of progress through early families had not been described in 1981 and few of the 2014 in the taxonomy of larval fishes of the marine Indo- existing descriptions met desirable quality criteria. In 2014, Pacific during the life of the Indo-Pacific Fish Conference we are fortunate to have hard-copy identification guides (IPFC) series, starting in 1981. This 33 year period has that cover a variety of Indo-Pacific regions, and from areas been an active time for larval-fish taxonomy, not only in outside the Indo-Pacific that include Indo-Pacific taxa, and the Indo-Pacific, but also worldwide. During this period a are therefore highly relevant to the Indo-Pacific researcher. need was identified and partially filled for larval-fish Hundreds of descriptions have been published in conven- identification guides to document for a range of potential tional journals, and the overall quality of descriptions is users, primarily fishery biologists, the hard-won ability to much improved. Larvae in 83 % of Indo-Pacific fish fam- identify fish larvae of a generation of larval-fish biologists, ilies that possess a pelagic larval stage have now been primarily those working in fishery agencies and to a lesser described. Importantly, much of this information is freely extent at universities and museums. In addition, a number available on the www, and we are beginning to see the of enthusiastic workers not employed as larval-fish biolo- development of interactive websites that assist the user to gists have made major contributions to larval-fish taxon- identify fish larvae.