REARING YOUNG MENHADEN 

 IN THE LABORATORY 



The foregoing field and laboratory studies 

 provided the necessary technical information 

 for us to establish and successfully rear Atlan- 

 tic menhaden larvae through and beyond meta- 

 morphosis in captivity. Feeding was begun 

 about 12 hours after larvae were established in 

 an aquarium. The maintenance ration was 

 varied according to the developmental stage of 

 the fish. Larvae were fed a daily ration of 15 

 to 20 copepods (chiefly Centropages and Acar- 

 tia, 0.5 to 1.3 mm. greatest dimension) or 30 

 to 50 Arteiyiia nauplii per larva. At the onset 

 of metamorphosis, the animal diet was supple- 

 mented with natural phytoplankton pumped 

 into the aquarium from nearby intertidal 

 waters. The pumping rate was adjusted to pro- 

 vide a daily minimum of 17 liters of water per 

 fish. After metamorphosis was completed, a 

 slurry consisting of 10 parts menhaden meal 

 and 1 part pureed clam (Mercenaria merce- 

 naria) was substituted for the co-pepod-Artemia 

 nauplii component and fed at a ratio of 1 to 20, 

 based on the total estimated weight of the fish 

 in an aquarium. 



The handling and feeding procedures de- 

 scribed in this paper can provide healthy stocks 

 of young menhaden in different developmental 

 stages for laboratory research. 



SUMMARY 



This paper covers the food of young Atlantic 

 menhaden, changes in the alimentary tract and 

 related body structures during their meta- 

 morphosis from larvae to juveniles, and labora- 

 tory studies of feeding, digestion, and associ- 

 ated responses of the young fish. 



The alimentary tracts in 592 Atlantic men- 

 haden larvae collected at Indian River Inlet, 

 Del., were examined for food. More than half 

 of the tracts were empty. Contents of 243 

 tracts that contained food consisted almost en- 

 tirely of copepods, chiefly Centropages. Gener- 

 ally, larger larvae fed on larger copepods, and 

 greater numbers of copepods in tract contents 

 were associated with daylight and evening 

 hours. Food items generally reflected the com- 



position and relative abundance of individual 

 copepod genera in the plankton. Although phy- 

 toplankters were abundant at the Inlet, larvae 

 did not eat them. 



Young menhaden changed their food habits 

 during metamorphosis within the estuaiy. Ali- 

 mentary tract contents of 20 larvae and 31 

 early-stage prejuveniles consisted almost en- 

 tirely of copepods, chiefly Acartia. Tract con- 

 tents of late-stage prejuveniles and juve- 

 niles consisted mostly of pennate and centrate 

 diatoms, dinoflagellates, and amorphous plant 

 materials. In general, major food items identi- 

 fied in the alimentary tracts also were the more 

 abundant organisms in the water. 



Metamorphosis of Atlantic menhaden is dis- 

 tinguished by the development of a highly spe- 

 cialized gill raker-alimentary tract complex. 

 The mouth is relatively large at all stages of 

 development. Prominent maxillary and dentaiy 

 teeth are present in larvae. The teeth become 

 nonfunctional during late metamorphosis and 

 eventually disappear. Gill rakers are rudimen- 

 tary in larvae, but increase in length, number, 

 and complexity during metamorphosis. Pha- 

 ryngeal pockets appear during metamorphosis. 

 The alimentary tract of larvae is nearly a 

 straight tube. In prejuveniles the tract begins 

 to fold forward, the muscularized stomach 

 (gizzard) starts to develop, and many pyloric 

 caeca become evident. In juveniles the intestine 

 forms several coils, pyloric caeca increase in 

 number and length, and fat deposits usually 

 surround the caeca and lie between the folds 

 of the intestine. 



Observations on Atlantic menhaden in cap- 

 tivity confirmed that larvae and early-stage 

 prejuveniles feed selectively on living prey. 

 They capture their prey by flexing and striking 

 like a snake. An individual larva may ingest 

 as many as 15 copepods, but the average was 

 10. Larvae pi-eferred copepods, but also fed on 

 Artemia and Balamis nauplii. Late-stage pre- 

 juveniles and juveniles feed mainly by filter- 

 ing plankton in the water. They disperse while 

 feeding, but reassemble in a tight school when 

 they have exhausted the food supply. 



Laboratory studies of selected responses of 

 Atlantic menhaden larvae suggest that the ab- 

 sence or low numbers of food organisms found 



510 



U.S. FISH AND WILDLIFE SERVICE 



