FISHERY BULLETIN: VOL. 73, NO. 3 



present at the posterodorsal corner of the basioc- 

 cipital in all bonitos (Figures 20-24). Godsil (1954) 

 first noted this feature, "a deep-rimmed, crater- 

 like depression in the basioccipital," and stated 

 that "This character is sufficient to separate Sarda 

 from any species of the Plecostei." In 1955, Godsil 

 modified this statement to ". . . it is not a positive 

 diagnostic generic character." In comparing this 

 basioccipital depression with other scombrids, we 

 found it to be diagnostic of bonitos. In Auxis, 

 Euthynnus, Katsuwonus, and Thunnus only a 

 shallow concave surface is present; Scom- 

 beromorus and Acanthocybium have small 

 foramina on the corresponding position of the 

 basioccipital. Grammatorcynus has a similar 

 depression but it is much shallower. 



Exoccipital.-The exoccipitals connect the skull 

 to the first vertebra dorsally. The exoccipital ar- 

 ticulates with the epiotic and supraoccipital bones 

 anterodorsally, the intercalar laterally, and with 

 the other exoccipital posterodorsally. In ventral 

 view, the exoccipital articulates with the prootic 

 anteriorly, basioccipital medioventrally, and in- 

 tercalar laterally. In posterior view, the foramen 

 magnum is framed by the exoccipitals. Dorsally, a 

 small foramen is present at the medioposterior 

 corner of the exoccipital and it opens into the brain 

 cavity. The exoccipital bones are similar, with an 

 intermuscular bone attached, in all bonitos except 

 Gymnosarda which has none and Sarda which has 

 two (Figure 12). 



OTOLITHS.-The first figures of bonito otoliths 

 were presented by Shepherd (1910a, b) who illus- 

 trated the asteriscus and sagitta of Sarda sarda 

 along with other miscellaneous eastern Atlantic 

 species, but his figures are too small and poorly 

 defined to be of any comparative value. Chaine 

 (1957) published good figures of the sagittae of 

 Sarda sarda as well as two species of Scomber, two 

 of Thunnus, and Scomberomorus tritor. Bauza 

 Rullan (1961:155-156, pi. 1, figs. 7-10) also illustrat- 

 ed the sagitta of S. sarda. Two studies include 

 information about intraspecific variation in the 

 shape of bonito sagittae. Chaine (1957) discussed 

 variation in S. sarda; Kuo (1970:125, fig. 7) showed 

 considerable variation with outline sketches of 

 sagittae from the left and right sides of 47 S. 

 chiliensis from California in an age and growth 

 study. Fitch and Craig (1964) made the first com- 

 parative study of scombrid otoliths when they 

 compared the sagittae of eastern Pacific scombrids 



in an attempt to assess the relationships of 

 Allothunnus fallai. They found that scombrid 

 sagittae, except for Scomber japonicus, have a 

 long thin rostrum, finely serrate margins, and a 

 deep sulcus on the inner face. Among bonitos, they 

 compared the otoliths of Allothunnus and three 

 species of Sarda {chiliensis, orientalis, and sarda). 

 Allothunnus and S. chiliensis were illustrated. 



Specific Characters.-We calculated proportions 

 of the sagittae as percent of the otolith (sagitta) 

 length (OL) in fork length and the greatest height 

 (H) in length of sagitta and in length of rostrum 

 (R). 



i^L (mm) OL/FL{%) H/OL(%) H/R(%) 



(n= 1 unless otherwise noted) 



The sagitta of Orcynopsis is the largest among 

 the bonitos relative to fork length. It has a ridge 

 extending from the postdorsal part of the outer 

 surface to the middle of the otolith. It also has the 

 shortest and widest rostrum and the deepest sul- 

 cus of any bonito (Figure 29b). 



The sagitta of Cybiosarda is larger and heavier 

 than Sarda. It is similar in size to Orcynopsis but 

 has a longer and thinner rostrum. Cybiosarda has 

 two ridges extending from the middorsal and 

 posteroventral parts of the sagittae toward the 

 ventral and middorsal areas respectively (Figure 

 29a). The latter one seems to be weaker. Both 

 Cybiosarda and Orcynopsis are distinct in having 

 a winglike flange which extends outward and 

 forms a small platform at the posterodorsal mar- 

 gin on the inner side. 



The sagittae in the species of Sarda are small 

 and have similar outlines (Figure 29c, d). A 

 pyramidlike ridge is present in the middle of the 

 posterior half of the sagitta. They also have the 



Figure 29.-Sagittae of six species of Sardini, upper figure of 

 each pair is the outer view, lower figure the inner view, a 

 Cybiosarda elegans, New South Wales, 365 mm FL. b. Orcynop- 

 sis unicolor, Tunisia, 567 mm FL. c. Sarda orientalis, Tokyo, 35( 

 mm FL. d. Sarda sarda, Azores, 418 mm FL. e. Gymnosarda 

 unicolor, Marshall Islands, f. Allothunnus fallai, Tasmania, 77£ 

 mm FL. (Scale indicates 1 mm.) 



552 



