Xenocongrid Eel Larvae in the Western North Atlantic1
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BIOLOGICAL INVESTIGATIONS OF THE DEEP SEA. 44. XENOCONGRID EEL LARVAE IN THE WESTERN NORTH ATLANTIC1 DAVID G. SMITH Institute of Marine Sciences, University of Miami ABSTRACT The leptocephalous larvae of the eel family Xenocongridae in the west- ern North Atlantic Ocean are identified and characterized. They are shown to form a compact and relatively uniform group. Larvae of six of the seven known western Atlantic species were found. Chilorhinus suensoni and Kaupichthys hyoproroides were common, while Kaupichthys nuchalis, Chlopsis bicolor, Robinsia catherinae, and Catesbya pseudomuraena were rarer. No leptocephali of Chlopsis dentatus were found. Although other authors have placed Chilorhinus as a separate family, the morphology of the larva suggests that it is a typical xenocongrid, and it is so treated. Lep- tocephalus hyoproroides Stromman is shown to be the larva of Kaupichthys diodontus (including K. at/anticus), and is accepted as the valid name of the species. The nomenclatural problem raised by the priority of names based on leptocephali is discussed. Keys to the xenocongrid eels of the western North Atlantic, both larvae and adults, are given. Station data and counts and measurements are given for all specimens, and each species is illustrated. INTRODUCTION The eel larvae or leptocephali are among the most conspicuous and char- acteristic components of tropical and subtropical plankton, yet they remain relatively poorly known. This is correlated with the uncertain taxonomy of the adults. The literature on eel taxonomy is widely scattered and much of it, especially the older works, is inadequate. The current need is for comprehensive treatment of eel families covering both larvae and adults. This report is an attempt to summarize the larvae of one family, the Xeno- congridae, in the western North Atlantic. The tropical western North Atlantic is an area well suited to studies of this sort. In the richness of its marine fauna it is second only to the vast tropical Indo-Pacific region. In addition, its boundaries are well defined, both geographically and faunistically. Much of the material reported on here was collected in the Straits of Florida, a particularly favorable area of study. The Florida Current flows within a few miles of the coast near Miami, providing easy access to oceanic plankton. The area has been in- tensively collected by the Institute of Marine Sciences of the University of 1Contribution No. 1018 from the Institute of Marine Sciences, University of Miami. This paper is one of a series resulting from the National Geographic Society-University of Miami Deep-Sea Biol- ogy Program. This stUdy is part of a thesis presented to the faculty of the University of Miami in partial fulfillment of the requirements for the degree Master of Science. 378 Bulletin of Marine Science [19(2) Miami over the past several years, and a sizeable collection of leptocephali has been accumulated. The water of the Florida Current comes partly from the Gulf of Mexico and the Caribbean Sea and partly from the open Atlantic, so it likely contains larval representatives of all the western North Atlantic eels. Even those species which normally occur only along the South American coast will occasionally be carried north into the Gulf Stream. The recognition of a large series of xenocongrid eel larvae coincided with the discovery of important new information on xenocongrid adults. The opportunity was present for the first time to identify and characterize the leptocephali of the xenocongrid eels of the western North Atlantic. ACKNOWLEDGMENTS This report stems from a program of research on oceanic fishes sup- ported by the National Science Foundation (NSF-GB-1350, GB-4389, GB- 70 15x), C. Richard Robins, principal investigator. Much of the material collected from the Research Vessels PILLSBURYand TURSJOPSwas obtained through grants NSF-G-23745 and GB-893 from the National Science Foun- dation to Dr. Donald P. de Sylva. Ship-time support was through NSF-GB- 1204, while travel and equipment was provided by the National Geographic Society-University of Miami Deep-Sea Biology Program. I wish to thank Dr. C. Richard Robins of the Institute of Marine Sci- ences for his encouragement and guidance throughout the course of this study. Drs. Frederick M. Bayer of the Institute of Marine Sciences and William J. Richards of the Bureau of Commercial Fisheries Tropical At- lantic Biological Laboratory reviewed the manuscript, and William N. Eschmeyer, now of the California Academy of Sciences, provided additional suggestions and criticisms. I have profited from discussions about eels and eel larvae with David M. Dean of the Institute. Finally, I extend a special word of appreciation to Dr. James E. Bohlke of the Academy of Natural Sciences of Philadelphia, without whose assistance and cooperation this study could not have been completed. MATERIAL Collections.-A total of 136 specimens of xenocongrid leptocephali was found in the collections of the Institute of Marine Sciences. These have come from various collecting operations carried out over a period of 14 years. The largest segment of the material (Table 1) stems from the work on oceanic fishes of the Florida Current carried out aboard R/V GERDA. The material from the R/V PILLSBURYwas taken on two cruises. Stations 100-191 were made on a cruise from Miami to Bermuda, and stations 343- 475 were run between Panama and Trinidad. 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