POTTHOFF and KELLEY: OSTEOLOGICAL DEVELOPMENT IN SWORDFISH 



adult counts (Table 16). Of 127 Xiphias (6.6 mm 

 ENL-668 mm ESL), 59 (46.4%) had seven bran- 

 chiostegals on both sides, 37 (29.2%) had eight 

 on both sides, and 31 (24.4%) had seven rays on 

 one side and eight on the other. 



SQUAMATION 



Larvae of Xiphias developed four rows of 

 scales on each side with smaller "scatter" scales 

 between the rows (Fig. 30). First to appear be- 

 tween 5.3 and 6.1 mm ENL were some ventral 

 "row" scales on the stomach. These scales were 

 added during growth anterior to the pectoral 

 symphysis and posteriorly to the ventral 

 hypurals. Dorsal row scales were first seen be- 

 tween 5.7 and 6.9 mm ENL, approximately be- 

 tween the 3d and 15th centrum. The addition of 

 dorsal row scales during growth was in an ante- 

 rior direction to the top of the head and in a pos- 

 terior direction to the dorsal hypurals. The two 

 lateral scale rows were first seen in some 

 specimens between 6.5 mm ENL and 8.6 mm 

 ESL, extending from the posterior border of the 

 pectoral fin to about the 16th centrum. Scales 

 were added anteriorly only to the dorsal lateral 

 row to about the operculum and posteriorly to the 

 urostyle. Scatter scales, between the dorsal, 

 ventral, and lateral scale rows first developed 

 between 6.2 and 7.1 mm ENL on the stomach just 

 posterior to the pectoral fin and dorsad to the 

 ventral scale row (Fig. 30). Scatter scales, which 

 were smaller than row scales, spread from the 

 stomach dorsad during growth until the left and 

 right sides in an area from the 4th centrum to the 

 18th centrum were covered (Fig. 30). Further 

 addition of scatter scales was then in an anterior 

 and posterior direction covering the whole body, 

 the sword, and the caudal fin rays at 61.5 mm 

 ESL, but not the pectoral, dorsal, and anal fins. 

 In our 187 mm ESL specimen the dorsal, anal, 

 and pectoral fin rays were covered with scatter 

 scales. In the literature, Arata (1954); Leim and 

 Scott (1966); Nakamura et al. (1968), and Palko 

 et al. (1981) stated that adult Xiph ias lack scales. 



Figure 30.— Larval and juvenile Xiphias gladius, depicting 

 the ontogeny of squamation. The size of scales was exaggerated 

 in proportion to the body. Starting from the top and going to 

 the bottom the specimens' lengths in millimeters are: 5.3 ENL, 

 6.2 ENL, 7.6 ESL, 11.5 ESL, 35.4 ESL, 188 ESL. 



Our largest 668 mm ESL specimen had scales 

 (Fig. 31), seen through the dissecting microscope 

 on a cleared and stained piece of skin. In this 

 specimen the row scales could no longer be dis- 

 tinguished from the scatter scales. 



Development of individual scales is similar for 

 the row and scatter scales, except scatter scales 

 start out smaller than row scales but increase in 

 size to equal the row scales during development. 

 Each scale starts as an oval-shaped structure 

 with one posteriorly recurved spine. During 

 development more posteriorly recurved spines 

 are acquired in a row at the center of the scales 

 and the scale margins become progressively 

 crenated (Fig. 32). Finally, in specimens >200 

 mm ESL the marginal scale crenations become 

 fewer and the recurved spines develop into blunt 

 stubs (Fig. 32). 



Individual row scales have approximately the 

 same number of spines in a developing specimen, 

 but this does not apply for the scatter scales. Our 

 largest 668 mm ESL Xiphias had developed 

 variable scales which had from one to seven 

 blunt stubby spines; row scales were not distin- 

 guishable from scatter scales in this specimen 

 (Figs. 31, 32). Arata's (1954) work on scale devel- 

 opment agrees with our findings. 



0.25mm 



Figure 31.— Enlarged view of the skin from a 668 mm ESL 

 Xiphias gladius, showing scales with two to six posteriorly re- 

 curved spines. White spaces between scales are skin. Anterior 

 is to the left. 



181 



