FISHERY BULLETIN: VOL. 80, NO. 2 



Figure 32.— Scales from Xiphias gladius, 

 showing ontogeny. Starting from left the 

 specimens' lengths in millimeters are: top, 

 5.4 ENL, 6.2 ENL, 25.1 ESL; bottom, 61.5 

 ESL, 225 ESL, 668 ESL. Each size in top 

 and bottom rows has an external view (top) 

 and a lateral view (bottom). 



0.01mm 



1.0mm 



0.10 mm 



1.0 mm 



1.0 mm 



DISCUSSION 



Xiphias gladius is a highly modified perci- 

 form fish which, in our opinion, should not be 

 placed as the monotypic family Xiphiidae in the 

 suborder Scrombroidei, as was done by Green- 

 wood et al. (1966). We agree with Gosline (1968) 

 and Fierstine (1974), who placed the monotypic 

 family Xiphiidae under the separate suborder 

 Xiphiioidei. However, Gregory and Conrad 

 (1937) compared Xiphias bones with those of 

 Istiophorus and concluded that xiphiids and 

 istiophorids are separate but parallel families of 

 common scombroid stock. G. David Johnson, who 

 examined the branchial arches of Xiph ias, istio- 

 phorids, and scombrids (unpubl. data), has evi- 

 dence that Xiph ias belongs with the scombroids. 

 We will discuss the modifications and variations 

 that we noted in Xiph ias and compare these with 

 other fish families. 



The pectoral fin position in Xiphias larvae is 

 lateral, but during growth to adults the fin 

 moves ventrad to an almost pelvic position. 

 Xiphias probably lost its pelvic fin during 

 phylogeny. Remnants of a basipterygium were 

 not found by us or other workers during develop- 

 ment of the larvae (Yasuda et al. 1978). 



Pectoral fin ray counts of the left and right 

 sides were equal or differed by one ray in 

 juvenile Xiphias. Similar results were obtained 

 for Archosargus (Houde and Potthoff 1976), 



Coryphaena (Potthoff 1980), and Scombrolabrax 

 (Potthoff et al. 1980). In tunas, larger differences 

 in pectoral fin ray counts between sides were 

 found (Potthoff 1974). 



With the publication of Dingerkus and Uhler's 

 (1977) cartilage staining technique, Fritzsche 

 and Johnson (1980) reported the development of 

 pectoral radials from a sheet of cartilage in 

 Morone. Swinnerton (1905) reported the same 

 for Salmo salar by using the "reconstruction in 

 wax from serial sections" technique; he called 

 the cartilaginous blade "fin-plate." We saw the 

 same happening in Xiph ias and labeled the sheet 

 of cartilage "blade" (Bl) in Figure 3. It is likely 

 that pectoral radials develop from a cartilagi- 

 nous blade in all Perciformes, and perhaps all 

 lower fishes. Starks (1930) reported a cartilagi- 

 nous blade (radial plate) in adult Dallia pecto- 

 ral is and Roberts (1981) in the salmoniform Sun- 

 dasalangidae; we believe this to be an example of 

 a neotenic structure. 



The pectoral girdle in Xiphias is reduced as 

 compared with a basic perciform pectoral girdle 

 such as that found in Coryphaena (Potthoff 1980) 

 and in at least some scombrids, e.g., Sardini 

 (Collette and Chao 1975), Acanthoeybium 

 (Conrad 1938), and Thu>nius(de Sylva 1955). In 

 Xiphias, the supratemporal and intertemporal 

 bones are absent and there is only one post- 

 cleithrum. 



Adult Xiphias have two dorsal and two anal 



182 



