EARLY DEVELOPMENT AND METAMORPHOSIS OF THE TEN-POUNDER 



ELOPS SAURUS LINNAEUS 



BY JACK W. GEHRINGER, FISHERY RESEARCH BIOLOGIST 



In the initial phase of the study of biological, 

 chemical, and oceanographic conditions in the 

 waters between Cape Hatteras and the Florida 

 Straits, the U.S. Fish and Wildlife Service, in 

 cooperation with the U.S. Navy Hydrographic 

 Office, the Office of Naval Research, the Georgia 

 Game and Fish Commission, and the Florida State 

 Board of Conservation, collected data and samples 

 with the MV T. N. GUI from January 1953 to De- 

 cember 1954. The second phase in the biological 

 study involved the identification of fish and plank- 

 ton organisms collected at sea. During the course 

 of such studies, forms are at times discovered 

 which have never been described. Understanding 

 the life histories of fishes is prerequisite to an un- 

 derstanding of the interrelationships of species 

 and to analysis of the biological potential of the 

 waters involved. The identification of the unde- 

 scribed forms often adds considerably to our 

 knowledge of a particular species. Such was the 

 case when leptocephali of the ten-pounder, Elops 

 saurus Linnaeus, 5.1 to 31.3 mm. in standard 

 length, were identified from plankton samples 

 taken in offshore waters during May, October, and 

 November, 1953 (fig. 1). 



The ten-pounder, E. saurus, undergoes a pecul- 

 iar larval development. The first post-yolk-sac lar- 

 val stage is a ribbon-like leptocephalus which 

 grows to about 40 mm., then shrinks in length to 

 about 20 mm. while metamorphosing into the adult 

 form. The development of the bonefish, Albula 

 vulpes (Linnaeus), and the tarpon, Tarpon atlan- 

 ticus (Valenciennes) 1 is similar. The shrinking of 

 the leptocephalid form of E. saurus during meta- 

 morphosis has been known for some time, as 

 shrinking and metamorphosing larvae are found 

 on the beaches and in the marshes. Leptocephali 

 prior to the period during which shrinking begins 

 have not previously been described. It has been 

 suggested (Hildebrand 1943) that the absence of 



1 In accordance with Bailey (1951), single authority is used. 

 Note. — Approved for publication May 7, 1958. Fishery Bulletin 



earlier stages of the ten-pounder in inshore waters 

 indicates offshore spawning and early growth. 

 This is substantiated by leptocephali of E. saurus 

 5.1 to 31.3 mm. in standard length in the plankton 

 samples taken in offshore waters along the south 

 Atlantic coast of the United States. 



In Georgia, shrinking larvae appear in seine 

 collections from the open beach beginning in 

 March or April. Within a few weeks, they appear 

 in marsh collections, and are present in marsh col- 

 lections through metamorphosis. Beach collec- 

 tions contain only occasional larvae after May, but 

 some have been found in late October. During 

 May of 1953 several larvae in the shrinking stage, 

 about 30 to 40 mm. in standard length, were reared 

 through metamorphosis in the laboratory. Other 

 larvae, which were undergoing or had undergone 

 metamorphosis before capture, were maintained 

 in laboratory aquaria for varying periods of time. 

 A developmental series (from leptocephalus to 

 adult) was compiled from plankton samples, lab- 

 oratory experiments, and seine samples collected 

 over a period of 4 years. 



This paper describes and illustrates a develop- 

 mental series from a 5.3-mm. leptocephalus to a 

 380- mm. adult (figs. 2 to 17), changes in rates of 

 growth of various body parts, and changes in body 

 structures during development ; and gives selected 

 measurements and meristic values for leptoce- 

 phali to adults, results of laboratory growth ex- 

 periments, and seasonal distribution of larvae. 



A review of important contributions to our 

 knowledge of the larval development of the ten- 

 pounder (E. saurus), the bonefish (A. vulpes), the 

 tarpon (T. atlanticus), and some closely related 

 Pacific forms follows : 



Dr. C. H. Gilbert in 1889 first identified the 

 leptocephalid larva of bonefish, A. vulpes, but it 

 was 1905 before figures and descriptions prepared 

 from his material were presented by Jordan, and 

 in 1907 by Gill. Subsequently, various authors 

 155. 619 



