Ontogeny, Systematics, and Phylogeny 

 D. M. Cohen 



THE work of Ahlie and his students and colleagues has brought 

 to the fore great amounts of descriptive information about 

 the early life history (ELH) stages of fishes gathered over many 

 years. These data are of broad provenance, many being the 

 results of original research by the Ahlstrom school, others being 

 taken from the literature. Only a scientist with Ahlie's capabil- 

 ities—an extensive knowledge of fishes and their ontogeny, a 

 fine sense of order in nature, and a critical intellect— could per- 

 ceive pattern in the bewildering diversity represented by the 

 early life history stages of fishes. As would any good scientist, 

 Ahlie questioned the meaning of these patterns, and it is chiefly 

 to further this inquiry that this symposium was convened. 



Most students of comparative fish ontogeny know more about 

 adult fishes than ichthyologists who study adults know about 

 larval fishes; they have to. Ahlie stated in his lectures. "Larval 

 taxonomy is just an adjunct to adult taxonomy and you have 

 to start with the adults to know the larvae." Early on he dis- 

 covered that data from early life history studies did not always 

 confirm classifications based on adults alone. We all want to 

 know which data sets most closely approximate phylogenetic 

 relationships; how apparent conflicts best can be resolved; how 

 the data of ontogeny can be integrated into the overall field of 

 fish systematics? Answering these questions is not easy, espe- 

 cially within the framework dictated by the widespread adoption 

 of new methodologies in systematics, which claim to require 

 more stringent evaluation of characters than has been heretofore 

 customary. Many traditional character suites are being rejected 

 for purposes of elucidating phylogenies, and new data are needed 

 for testing. Our purposes m this volume are to state the bases 

 for what has come to be called larval fish taxonomy and to 

 consider the systematics of various groups of fishes in terms of 

 the rich and virtually untapped store of data offered by the study 

 of early life history stages. 



My own objectives in the present paper are several. First of 

 all. I want to indicate the reasons, some obvious, some not, for 

 the nearly exclusive use of adult fishes in systematics, which has 

 prevailed until very recently. Secondly, I will briefly discuss the 

 conceptual and methodological framework of classification 

 within which early life history data is being used. Finally, I will 

 comment on the possible importance of early life history data 

 for the study of phylogeny with special reference to fishes. 



Why Has There Been So Little Use of 

 ELH Stages in Fish Systematics? 



The fact that most fish classifications are based entirely or 

 chiefly on the structure of adults was a source of concern to 

 Ahlie and remains so to many of us, although this Symposium 

 is an indication of positive change. I discuss below what may 

 be some of the reasons for a long preoccupation with adults. 



In the first place, zoologists have been studying adults for a 

 longer period of time than they have early life history stages. 

 Although the dim beginnings of classification are often placed 

 with Aristotle, it was the great naturalists Aldrovandi. Belon. 

 Gesner. and Rondelet who in their cataloging of nature provided 

 our earliest adult fish classifications. Several technological de- 

 siderata would have prevented the study of early life history 

 stages during the 1 6th century when these early scientists were 



at work. Even though lenses had been known for a long time, 

 appropriate microscopes were not invented until the 1 7th and 

 18th centuries (Singer, 1959) when another requisite advance 

 occurred, the use of alcohol and other fluids as a preservative 

 for zoological specimens (Singer, 1950). Techniques for clearing 

 flesh and staining bone and cartilage are modem acquisitions, 

 as is the use of x-ray photographs (Ahlstrom and Moser. 1981). 

 The invention of fine-mesh towing nets did not occur until 1 846 

 (Sverdrup. Johnson, and Fleming, 1942), deferring until rela- 

 tively recent times the availability of suitable collections of early 

 life history stages for scientific study. 



The rearing of early stages is another valuable component of 

 the study of larval fish taxonomy, and although fish culture is 

 an ancient art, the staging of fry and their preservation and 

 microscopic study is technology-dependent and relatively re- 

 cent. 



Lack of information on metamorphosis or of congruence of 

 larval and adult stages has also delayed the adoption of early 

 life history stages information into classification schemes. Of 

 course not many kinds of fishes demonstrate an ontogenetic 

 change as sudden and dramatic as do the eels, but the fact that 

 this particular transformation was not described until 1897 

 (Grassi and Calandruccio) indicates the long advance start held 

 by the use of adult stages. Even more recent have been discovery 

 of the Anoplogaster-Caulolepis relationship (Grey, 1955a), the 

 Gibberichthys-Kasidoron relationship (de Sylva and Eschmeyer, 

 1977), the Giganturidae-Rosauridae relationship (Johnson, this 

 volume), and the as-yet-unpublished identity of larval forms 

 such as Svetovidovia. These and other examples are described 

 in this volume. And indeed, even when the study of the devel- 

 opmental biology of vertebrates commenced, early emphasis in 

 the mid- 18th century was on classical embryology, the describ- 

 ing of processes and structures rather than on comparing them 

 (Rostand, 1964). Not until the early years of the present century 

 when fishery scientists began to use larval fishes in their inves- 

 tigations of commercial species and required identifications were 

 serious efforts made to compare data (Ahlstrom and Moser, 

 1981). 



Until Ahlie commenced his now famous courses on larval 

 fishes, there were few places where a student could learn about 

 them; hence, there are only rare instances of attention being 

 paid to any potential value they might have in solving problems 

 in systematics. By now, in contrast, there are courses and sem- 

 inars available in a number of universities on the study of ELH 

 stages of fishes. 



Another phenomenon that I believe has inhibited the use of 

 early life history stages in fish systematics is what I call the 

 curatorial mind set. Many curators of adult fish collections are 

 wary of microscopic specimens stored in vials. Although these 

 collections occupy small space, their maintenance and docu- 

 mentation are labor-intensive and their use is foreign to most 

 ichthyologists. There are many excellent collections of larval 

 fishes, but they are mostly in fishery, environmental and marine 

 biology laboratories— organizations that have no institutional 

 commitment to long-term collection storage. Collections that 

 document important publications or have potential value in 

 systematics should ultimately be deposited in a museum that 



