STUDIES OF MORPHOLOGICAL CHANGES 

 DURING METAMORPHOSIS OF YOUNG 

 MENHADEN 



As Atlantic menhaden larvae transform into 

 juveniles, they acquire scales, fin-ray comple- 

 ments, and the deep body form characteristic 

 of adults (Mansueti and Hardy, 1967). The 

 shift from a carnivorous to an omnivorous diet 

 during metamorphosis suggests that changes 

 also take place in structures directly concerned 

 with feeding and digestion. 



MATERIALS AND METHODS 



Changes in the morphology of structures as- 

 sociated with feeding and digestion were de- 

 scribed from counts or measurements as a func- 

 tion of fish length. The counts or measurements 

 were made on 196 specimens, 19 to 75 mm. 

 long, from the samples of fish used for the 

 food studies and included the following: 



Dentary teeth : Total along margin of left den- 

 tary. 



Fork length: Distance (1.0 mm.) from tip of 

 mouth to end of median rays in caudal fin. 



Gape height: Distance (0.1 mm.) between in- 

 ner margins of premaxillary and dentary 

 symphyses with jaws opened to a 65° 

 angle. 



Gape width: Distance (0.1 mm.) between in- 

 ner margins of jaw angles opened to a 65° 

 angle. 



Gill rakers: Total, including rudiments, along 

 first left gill arch. 



Length of the anterior alimentary tract: Dis- 

 tance (0.1 mm.), with tract extended, be- 

 tween posterior margin of pharynx and the 

 pylorus. 



Length of the posterior alimentary tract : Dis- 

 tance (0.1 mm.), with tract extended, be- 

 tween the pylorus and anus. 



Maxillary teeth: Total along margin of left 

 maxillary. 



Pyloric caeca: Total evaginations at juncture 

 of anterior and posterior alimentary 

 tracts. 



DEVELOPMENT OF THE DIGESTIVE SYSTEM 

 IN RELATION TO DIET 



We studied morphological changes in the 

 mouth, teeth, gill rakers, alimentaiy tract, and 

 pyloric caeca during metamorphosis and re- 

 lated these changes to the diet. 



Mouth 



The tenninal mouth of the Atlantic men- 

 haden larva has an elliptical opening and is 

 relatively large through later stages of de- 

 velopment (fig. 4). A median notch is present 

 on the upper jaw of larvae over 19 mm. long, 

 and the lower jaw is included in the upper one. 

 The mouth opening in 19-mm. larvae is about 

 1 mm.2; it increases to a maximum of about 

 7 mm.^ in prejuveniles and reaches about 

 20 mm.^ in 75-mm. juveniles. Because gape 

 height and width increase linearly with length 

 of the fish (fig. 5), the maximum dimension 



Figure 4. — Lateral view of the head of a 75-mm. (fork 

 length) juvenile Atlantic menhaden showing the 

 gape and the median notch on the upper jaw. 



FOOD OF YOUNG ATLANTIC MENHADEN IN RELATION TO METAMORPHOSIS 



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