CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES 



The inner gill rakers are knoblike, sometimes 

 with spicules or teeth on their distal ends (Figure 

 24a '-f'). Cynoscion regalis, Micropogonias un- 

 dulatus, and Menticirrhus saxatilis have broad, 

 short inner gill rakers, with the height not longer 

 than the width of the base. Cynoscion regalis and 

 Micropogonias undulatus have prominent 

 spicules at the distal ends of their inner gill rakers 

 (Figure 24b', d'). Menticirrhus saxatilis lacks 

 spicules on its inner gill rakers (Figure 24e'). 

 Larimus fasciatus, B. chrysoura, and Leiostomus 

 xanthurus have long inner gill rakers, with the 

 height longer than the width of the base. Larimus 

 fasciatus and B. chrysoura have prominent 

 spicules at the distal ends of their inner gill rakers 

 (Figure 24b', c'). Leiostomus xanthurus has mi- 

 nute spicules on its inner gill rakers (Figure 24f). 

 Furthermore, in Larimus fasciatus a small inner 

 gill raker is often present in between the larger 

 inner gill rakers (Figure 24a'). This is rather 

 common among western Atlantic sciaenids (Chao 

 in press). 



The lateral and inner gill rakers on the second to 

 fifth gill arches are similar in size and structure to 

 the inner gill rakers on the first gill arch. The gill 

 arches of these six species also differ in the relative 

 lengths of the epibranchial (upper) arm and 

 ceratobranchial (lower) arm (Figure 24). Leio- 

 stomus xanthurus has the shortest upper arm and 

 M. saxatilis has the shortest lower arm. The num- 

 bers and size of the gill rakers indicate that mid- 

 water feeders have lateral rakers longer than 

 those of bottom feeders. The relative lengths of 

 inner rakers are longer in fishes with higher num- 

 bers of lateral rakers, e.g., Larimus fasciatus and 

 Leiostomus xanthurus (Figure 24a', f; Table 6). 

 Although Micropogonias undulatus has the 

 strongest spicules on the lateral gill rakers (Fig- 

 ure 24d), the midwater feeders usually have better 

 developed spicules on the lateral rakers than the 

 bottom feeders (Figure 24). Higher numbers of 

 rakers (both inner and lateral) are associated with 

 filter feeding. 



Digestive Tract 



The digestive tract of sciaenids includes four 

 parts: esophagus, stomach, pyloric caeca, and in- 

 testine. The intestine usually has two loops (Fig- 

 ure 25), except that of C. regalis which is a straight 

 tube from stomach to anus (Figure 25B). The rela- 

 tive position and size of the stomach and intestine 

 vary with the amount of food present. The num- 



bers of pyloric caeca and the relative length of the 

 intestine may be correlated with feeding habits 

 (Suyehiro 1942). The relative length of the intes- 

 tine of these six species of sciaenid fishes (Table 7) 

 may be grouped into three general categories. 

 Cynoscion regalis has the shortest intestine, less 

 than half the standard length. Bairdiella 

 chrysoura has an intermediate intestine length. 

 Micropogonias undulatus, Menticirrhus saxatilis, 

 Larimus fasciatus, and Leiostomus xanthurus 

 have long intestines. The numbers of pyloric caeca 

 (Table 8) in these six sciaenid fishes show a similar 

 trend. Cynoscion regalis has the fewest pyloric 

 caeca, four or five. Bairdiella chrysoura and M. 

 saxatilis usually have 6 or 7, and Micropogonias 

 undulatus and L. xanthurus have 7 to 10 pyloric 

 caeca. Larimus fasciatus has the most, 10 or 11. 

 Larimus fasciatus and Leiostomus xanthurus 

 have both a longer intestine and more pyloric 

 caeca, but Larimus fasciatus is a midwater feeder 

 and Leiostomus xanthurus is a bottom feeder. 

 They both consume large numbers of small crusta- 

 ceans (see "Food Specialization" section). Cynos- 

 cion regalis has the shortest intestine and the 

 fewest pyloric caeca. Its diet is mainly composed of 

 large crustaceans and fishes. Thus, the relative 

 lengths of the intestine and the numbers of pyloric 

 caeca in these sciaenids may be correlated with 

 the size of the food rather than the feeding position 

 in the water column. 



TABLE 7. — Relative length of intestine in juveniles of six species 

 of sciaenids from the York River. 



Intestine length in % of SL 



Species 



SL (mm) Range 



SD 



N 



Cynoscion regalis 

 Bairdiella chrysoura 

 Micropogonias undulatus 

 Menticirrhus saxatilis 

 Larimus fasciatus 

 Leiostomus xanthurus 



35.2-152 35.5-49.6 40.24 3.07 36 



30.0-151 46 1-64 1 55.34 5.92 30 



35.5-145 52.3-88.6 65.57 6.56 39 



29.2-91.2 56.6-88.2 76.06 6.67 26 



35.3-99.8 73.1-97.7 83.87 9.08 14 



47.4-166 736-97.8 84.69 6.95 30 



TABLE 8. — Number of pyloric caeca in juveniles of six species of 

 sciaenids from the York River. 



Species 



(size in mm SL) 



456789 10 11 N x 



685 



