FOOD OF YOUNG ATLANTIC MENHADEN, BREVOORTIA TYRANNUS, 

 IN RELATION TO METAMORPHOSIS 



BY FRED C. JUNE' AND FRANK T. CARLSON,^ FISHERY BIOLOGISTS 



BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 



BEAUFORT, N.C. 28516 



ABSTRACT 



To rear this species in captivity required knowledge 

 of the kinds of organisms it ate. Larvae ate zooplankton 

 (copepods), but prejuveniles and juveniles fed chiefly on 

 phytoplankton. There were similarities as well as dif- 

 ferences between the alimentary tract contents of the 

 fish and the composition of the plankton community. 

 Changes in food habits during metamorphosis were 



Laboratory research is needed to determine 

 how specific environmental factors affect the 

 distribution, behavior, and survival of young 

 Atlantic menhaden {Brevoortia tyrannus) 

 after their entiy as larvae into estuarine nurs- 

 eries from oceanic spawning grounds (June 

 and Chamberlin, 1959). Before these young 

 fish can be successfully maintained in the labo- 

 ratory, it is necessary to know their diet re- 

 quirements. 



Previous investigators established that young 

 Atlantic menhaden feed on plankton. Peck 

 (1894) observed that stomach contents of juve- 

 niles (60 and 100 mm. long) collected near 

 Woods Hole, IMass., closely agreed with the 

 olankton in the surface waters. He also de- 

 scribed the specialized gill rakers that this 

 fish uses to strain minute organisms from the 

 water. Using radioisotope techniques, Chipman 

 (1959) determined that larvae were unable to 

 filter phytoplankton, but fed on larval brine 

 shrimp and on copepods. Juveniles (averaging 

 188 mm. long), on the other hand, could filter 

 phytoplankton cells (Nannochloris) as small 

 as 2 ^. Richards (1963a, 1963b) found crus- 

 taceans (chiefly Balanus larvae, Neomysis, and 



accompanied by gross morphological changes in the 

 alimentary tract and related structures. Laboratory 

 studies of larvae disclosed that their failure to feed at 

 low light intensities, their digestion rate, and their def- 

 ecatory response to capture and preservation probably 

 contributed to the high incidence of empty alimentary 

 tracts in field collections. 



the copepods Centropages, Paracalantis. Acar- 

 tia, and Temora) to be the principal food of 

 29 specimens (16-120 mm. long) from Long 

 Island Sound, N.Y. She reported no differences 

 in stomach contents of fish of different sizes. 

 None of the earlier investigators clearly 

 identified the changes in composition of diet 

 associated with the transformation of Atlantic 

 menhaden larvae into juveniles.-' Because our 

 principal aim was to establish techniques for 

 rearing laboratory stocks of these young fish 

 through metamorphosis for experimental pur- 

 poses, we needed to know their food require- 

 ments at the diffei-ent developmental stages 

 and the suitability of substitute foods. More- 

 over, in connection with studies of the estu- 

 arine ecology of young menhaden in progress 

 in Indian River, Del. (June, 1957), it was es- 

 sential to know their natural foods so as to 

 assess the relevant components of the plankton. 

 Finally, changes in morphology of the digestive 

 system that enable juveniles to feed on smaller 



' North Central Reservoir Investigations. Bureau of Sport Fisheries 

 and Wildlife, P. O. Box 698. Pierre, S.D. 57501. 



- Department of the Interior. Washington, D.C. 20240. 



'We follow the definitions of Mansueti and Hardy (1967). Larva: 

 The stage of development between hatching and attainment of the 

 adult fin-ray complements: our specimens ranged from 13 to about 

 liO mm. fork length. Prejuvenile: The intermediate stage between 

 larval and juvenile form: these ranged from about 30 to 40 mm. 

 fork length. Juvenile: Young fish after attainment of full adult 

 counts and before sexual maturation: the stage begins when the 

 body form closely approximates that of the adult and in our speci- 

 mens occurred at about 40 mm. fork length. 



Published March 1971. 



FISHERY BULLETIN: VOL. 68, NO. 3 



493 



