COLLETTE and CHAO: SYSTEMATICS AND MORPHOLOGY OF THE BONITOS (SARDINI) 



Magnuson and Heitz (1971) have clearly shown for 

 a number of species of Scombridae. The number of 

 gill rakers is easily countable and is an important 

 taxonomic character in the Sardini as well as 

 among other groups of the Scombridae. 



Allothunnus differs strikingly from other boni- 

 tos in having many more gill rakers on the first 

 arch, 72-80 compared to 8-27 (Table 7). The only 

 other scombrids that approach this high number of 

 gill rakers are Katsuwonus pelamis with 53-63 and 

 two species of the genus Rastrelliger, R. 

 kanagurta (Cuvier) and R. brachysoma (Bleeker), 

 with 48-68. As discussed under dentition, the high 

 number of gill rakers in Allothunnus is correlated 

 with a high number of teeth in both upper and 

 lower jaws. 



Cybiosarda, Orcynopsis, and Gymnosarda all 

 have few gill rakers (11-17), fewer than any other 

 bonitos except Sarda orientalis (8-13). 



Number of gill rakers is a valuable character 

 within the genus Sarda. The largest difference is 

 between S. orientalis (8-13) and S. chiliensis 

 (23-27), which is particularly useful in the eastern 

 Pacific where the tropical S. orientalis can be 

 separated from S. chiliensis to the north and south 

 on the basis of fewer gill rakers (and, in a similar 

 fashion, jaw teeth). Sarda australis, which has 

 been considered a subspecies of S. chiliensis by 

 many authors, is intermediate in number of gill 

 rakers (19-21) between S. chiliensis and S. orien- 

 talis but completely separated from both. There 

 are also differences below the species level: Sarda 

 sarda in the western Atlantic averages fewer 

 (North America, 17.6; South America, 18.7) gill 

 rakers than the other four populations, especially 



the Mediterranean -Black Sea (20.9) and Gulf of 

 Guinea (20.9). 



Inner Gill Rakers. -The inner surface of the 

 hypobranchial, ceratobranchial, and epibranchial 

 bones of the first gill arch supports a series of 

 tubercles, the inner gill rakers. The strongest 

 tubercle usually occurs at or near the junction of 

 the upper and lower arches on the lower arch. The 

 number of inner gill rakers (Table 8) is correlated 

 with the number of gill rakers on the first gill arch 

 (Table 7). Allothunnus has the longest, thickest, 

 and most numerous inner gill rakers (49-56). In 

 many specimens of Cybiosarda elegans and Sarda 

 orientalis the inner gill rakers are degenerate 

 with only a few small tubercles present. We agree 

 with Godsil (1954, 1955) that the counts are diflficult 

 to make in Sarda with any consistency. Godsil 

 used the presence of the inner gill rakers ("gill 

 teeth") as a character to distinguish Sarda 

 chiliensis from S. orientalis in the eastern Pacific. 

 Gymnosarda completely lacks inner gill rakers, 

 but many small conical teeth are present around 

 the base of the gill rakers. These small teeth are 

 also present around the base of the gill rakers in 

 the other bonitos but they are much smaller than 

 in Gymnosarda. 



AXIAL SKELETON 



This section is divided into six parts: vertebral 

 number, vetebral column, infracentral grooves, 

 ribs and intermuscular bones, caudal peduncle 

 keels, and caudal complex. 



Table 8.-Total number of inner gill rakers on the first gill arch in species of Sardini. 



571 



