plankters than larvae had not been previously 

 described. Most of our research on these sub- 

 jects was done at the former Field Station of 

 the BCF (Bureau of Commercial Fisheries) at 

 Millville, Del., in 1960 and 1961. 



STUDIES OF ALIMENTARY TRACT 

 CONTENTS AND PLANKTON 

 COMPOSITION 



We determined the natural foods of young 

 Atlantic menhaden by examining the alimen- 

 tary tract contents of wild specimens. Analy- 

 sis of concomitant plankton samples enabled 

 us to compare the organisms available and 

 those actually ingested. 



MATERIALS AND METHODS 



Alimentary tracts of 738 young menhaden 

 were examined for food. Of this number, 592 

 came from larvae chosen at random from 

 catches made with l-m.-diameter nylon plank- 

 ton nets (mesh aperture 0.90 mm.) in the 

 mouth of Indian River, Del., between Novem- 



* The use of trade names in this publication does not imply en- 

 dorsement of commercial products. 



ber 1960 and May 1961 (table 1). The rest 

 came from larvae, prejuveniles, and juveniles 

 captured by haul seines within this estuary 

 from April to June 1961 (table 2). 



Preservation techniques varied with the size 

 of the fish and character of the alimentaiy 

 tract contents. Larvae were preserved intact 

 in 5 percent Formalin * buffered with borax. 

 The alimentary tract from most prejuveniles 

 and juveniles was removed, slit longitudinally, 

 and preserved in a chrom-osmic mixture (Gray, 

 1954) ; some tract contents were only chilled 

 prior to examination. 



The fraction and portion of the tract con- 

 tents examined also varied with the develop- 

 mental stage of the fish. The alimentary tract 

 of larvae was opened, the percentage fullness 

 estimated, and the location of contents within 

 the tract noted. Organisms were removed, iden- 

 tified, counted, and measured; and the relative 

 volume of each item was estimated. With pre- 

 juveniles and juveniles, only the contents of the 

 esophagus and anterior stomach were exam- 

 ined, because we could recognize few organisms 



Table 1. — Samples of Atlantic menhaden larvae for food studies collected in plankton nets at Indian River Inlet, 



Del, November 1960 to May 1961 



494 



U.S. FISH AND WILDLIFE SERVICE 



