CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES 



undulatus, Menticirrhus saxatilis, and Leiostomus 

 xanthurus feed on the bottom (Figure 20D-F). The 

 relative length of the premaxilla and dentary 

 bones decreases and the height of the anterior 

 dorsal process of the premaxilla increases from 

 fishes adapted to feed in "midwater" to those 

 adapted to feed on the bottom (Figure 21). This 

 trend is also evident in the relative mouth size and 

 angle (Figure 21 A-F). An index number (Table 5), 

 the length of the upper jaw multiplied by the 

 length of the lower jaw then divided by head 

 length, decreases through the series of species to- 

 wards a bottom feeding habit. 



Bottom feeders, M. undulatus, L. xanthurus, 

 and Menticirrhus saxatilis, have protrusible pre- 

 maxillae (Figures 20D-F', 21D-F). This can be 

 advantageous in getting the mouth opening close 

 to food that is to be sucked in from the bottom 

 (Alexander 1967). Midwater feeders, Larimus fas- 

 ciatus, C. regalis, and B. chrysoura, lack the pro- 

 trusibility of the premaxillae (Figures 20A-C; 

 21A-C); C. regalis andB. chrysoura may compen- 

 sate for this with faster swimming speed. Gero 

 (1952) and Nyberg (1971) have discussed this as- 

 pect in detail. Larimus fasciatus differs from other 

 sciaenids studied here. It may swim around with 

 its mouth open using its gill rakers as a filter 

 similar to that of Engraulis (Gunther 1962). 



Dentition 



Teeth on the premaxilla and dentary are impor- 

 tant in capturing prey whereas the pharyngeal 

 teeth are used for grinding and/or transporting 

 food to the esophagus. Members of the genus 

 Cynoscion usually have a pair of enlarged canine 

 teeth at the tip of the upper jaw (Figures 21B, 

 22B). Other teeth are conical and present on nar- 

 row bands of the premaxilla and dentary. The tips 

 of the upper and lower jaws are broad and have 

 several rows of teeth which decrease in number to 

 a single prominent row on the narrower posterior 



portion of the jaws. Small teeth also develop inside 

 the larger row of upper jaw teeth and outside the 

 lower jaw teeth. Bairdiella chrysoura has a nar- 

 row band of teeth similar to C. regalis but lacks 

 large canine teeth at the tip of the upper jaw (Fig- 

 ure 22C). Micropogonias undulatus, Leiostomus 

 xanthurus, and Menticirrhus saxatilis have vil- 

 liform teeth set in broad bands on the premaxillae 

 and dentaries, and also lack canine teeth (Figure 

 22D-F). The teeth on the outer row of the pre- 

 maxillae and inner row of the dentaries are 

 slightly enlarged. Larimus fasciatus is unique in 

 having only one or two rows of small teeth on both 

 jaws (Figure 22A). 



Pharyngeal teeth are generally conical in sci- 

 aenids (Figure 23). The lower pharyngeal teeth 

 form a pair of separate narrow tooth patches and 

 are situated on the most medial pairs of cerato- 

 branchial bones. The upper pharyngeal teeth 

 occur mainly as two pairs of patches on the two 

 most medial pairs of epibranchial bones. The 

 pharyngeal plates are relatively small and narrow 

 in L. fasciatus and C. regalis compared with the 

 other sciaenids examined (Figure 23 A, B). The 

 pharyngeal teeth of L. fasciatus and C. regalis are 

 sharp, conical, and directed backward, but in B. 

 chrysoura the pharyngeal teeth are blunt and the 

 median ones are enlarged (Figure 23C). Micro- 

 pogonias undulatus has much stronger and more 

 enlarged pharyngeal teeth along the median rows 

 (Figure 23D). Menticirrhus saxatilis has fine and 

 sharp pharyngeal teeth (Figure 23E). Leiostomus 

 xanthurus develops molariform teeth medially on 

 the pharyngeal plates (Figure 23F). These sequen- 

 tial morphological differences in pharyngeal teeth 

 reflect the feeding niche differentiation from mid- 

 water to benthic. 



Gill Rakers 



Gill rakers on the branchial arches of fishes are 

 important in protecting the delicate gill filaments 



TABLE 5.— Relative size of mouth and eye diameter in juveniles of six species of sciaenids from the York 



River. 



1 1ndex of mouth size = (upper jaw length x lower jaw length)/head length. 



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