CHAOandMUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES 



feeding niches of any fish family in the 

 Chesapeake Bay. The four most abundant species, 

 Cynoscion regalis, Bairdiella chrysoura, Micro- 

 pogonias undulatus, and Leiostomus xanthurus, 

 are most abundant in the estuary from late spring 

 to fall, especially young-of-the-year and yearlings 

 (see previous sections). Under these conditions, 

 food resources may be limiting and division of 

 feeding niches may have evolved in order to reduce 

 competitive exclusion among the dominant 

 species. Fishes that are closely related and show 

 feeding niche segregation also often show mor- 

 phological differentiation in the feeding ap- 

 paratus (Keast and Webb 1966; Davis 1967; Keast 

 1970; Davis and Birdsong 1973; Emery 1973). This 

 section of the paper examines the morphology of 

 the feeding apparatus in Larimus faseiatus, C. 



regalis, B. chrysoura, M. undulatus, Menticirrhus 

 saxatilis, and Leiostomus xanthurus to test the 

 hypothesis that adaptations to feeding niche divi- 

 sion have evolved among those six species. 



Characters important in feeding were examined 

 including mouth position and size, dentition, 

 number of gill rakers, and intestine length. These 

 directly affect the size and kind of food ingested 

 and digested. Other accessory characters 

 examined were the pore and barbel system on the 

 snout and/or lower jaw, the nares, and body shape. 



Mouth Position 



Mouth position and size of the opening limit the 

 size of prey and habitats in which a predator can 

 effectively capture prey. These characters were 



B 



B' 



FIGURE 20. — Mouth position and opening in juveniles of six species of sciaenids: A, A', a, a', Larimus fasciatus; B, B', b, b', Cynoscion 

 regalis; C, C ', c, c ', Bairdiella chrysoura; D, D ', d, d ', Micropogonias undulatus; E, E ', e, e '. Menticirrhus saxatilis; F, F', f, f ', Leiostomus 

 xanthurus. A-F, mouth closed. A '-F' mouth wide open. Front view of mouth openings ( lower case letters) in corresponding positions. 



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