finned fish. In general, application of the pectoral 

 area equation to the smaller SIO fish (Table 1) does 

 not result in close correspondence between estimated 

 and observed areas, suggesting that the relationship 

 derived from larger individuals does not fit smaller 

 yellowfin tuna. The relative length of the pectoral 

 fin in yellowfin tuna changes abruptly with size In 

 fish between about 35 and 42 cm L, pectoral fin 

 length should normally be about 25% L (Gibbs and 

 Collette 1967, fig. 26). This contrasts with the value 

 for the one-finned fish of 20.5% L. 



The left pectoral girdle is present, but clearly ab- 

 normal in gross examination. The posttemporal is 

 reduced in overall size; the upper (pterotic) fork is 

 somewhat reduced and lower (epiotic) fork weakly 

 developed and without a flattened articular surface 

 The rear margin of the supracleithrum is eroded, and 

 the lateral surface rough. The cleithrum is almost 

 as large as that of the right side, but the lateral 

 groove for muscle attachment is reduced, and the 

 upper process that normally curves out over the 

 scapula is absent. The scapula is a block of bone with- 

 out an articular facet for the first pectoral ray, and 

 the scapular foramen is represented by a slit in the 

 lateral surface The coracoid is much reduced pos- 

 teriorly, and its reduced lower process is tightly ap- 

 plied to the cleithrum so that the interosseus space 

 is almost absent. The pectoral actinosts may be 

 represented by a small lump of bone that is tightly 

 attached to the scapula. A number of bone chips 



were embedded in the tissue overlying the pectoral 

 girdle The postcleithra appear to be essentially 

 normal. 



Elements in the left side of the pelvic girdle are 

 larger and have a different orientation from those 

 of the right. Also, the left pelvic fin is both smaller 

 in area and shorter than the right (Fig. 2). Pelvic fin 

 lengths and areas in the one-finned fish are left 2.9 

 cm, 3.2 cm 2 ; right 3.5 cm, 4.7 cm 2 . Comparable 

 values for the 37.0 L SIO fish are left 3.5 cm, 4.5 

 cm 2 ; right 3.7 cm, 4.9 cm 2 . X-rays showed that the 

 centra of vertebrae 19 and 20 are abnormal (Fig. 3). 

 They lie parallel to one another and overlap by about 

 80% in the horizontal axis. There is considerable ero- 

 sion of the adjoining surfaces of the two centra and 

 their neural and haemal spines are displaced. This 

 deformity, together with the reduced left pelvic fin, 

 the absence of a left pectoral fin, and a deformed 

 left pectoral girdle, suggests the presence of a con- 

 genital malformation. 



As would be expected from our density findings, 

 the gas bladder of the one-finned fish was small (17 

 x 5 mm, length x diameter), but about the same 

 size as that of other yellowfin tuna (Magnuson 1973, 

 1978). Finally, we found no differences in the left and 

 right body myotomes. The total red muscle was 

 estimated to be 6.7% of wet weight, which is with- 

 in the 95% confidence limits of the value reported 

 for yellowfin tuna (5.2-7.8%) by Graham et al. 

 (1983). 



Figure 2— Anterior ventral view showing the 

 reduced size of the left pelvic fin. 



466 



