FISHERY BULLETIN: VOL. 72. NO. 2 



PECTORAL GIRDLE 



LATERAL LINE 



T. alalunga 



71 atlantlcus 



specific ranges do not overlap except for T. ala- 

 lunga with the Thunnus spp. complex. Thus, 

 the ceratobranchial count, if available, should 

 take precedence over the vertebral count. The 

 first haemal postzygapophysis may be very small 

 and high magnification should be used when view- 

 ing this character. 



All characters listed in Table 13 are available 

 for identification on specimens past 21 to 23 mm 

 SL. The following features can be used to 

 identify a specimen: 



T. thynnus 



T. spp. 



Figure 13. — Outline of the lateral line for juveniles of the 

 Thunnus species. Each pair of dashes in the lateral line 

 represents one scale. 



count of gillrakers over the ceratobranchial. The 

 juveniles can be identified as follows: 



Character 



Number precaudal + caudal 



vertebrae 

 Ceratobranchial filled with 



11-12 rakers 

 First closed haemal arch 



Pterygiophore pattern 



First haemal postzygapophysis 



Species separated 



T. atlanticus from T. thynnus, 

 T. alalunga, Thunnus spp. 



T. atlanticus + Thunnus spp. 

 from T. thynnus + T. ala- 

 lunga 



T. alalunga fromT. thynnus + 

 Thunnus spp. 



T. alalunga + T. atlanticus 

 from T. thynnus + Thunnus 

 spp. 



Juveniles in this size range are easier to identify 

 for two reasons. First, they are further advanced 

 in development, they stain better, and the charac- 

 ters are more readily discernible. Second, the 

 availability of two additional characters permit 

 cross-checking so that it is possible to identify 

 "one character" variants. For example, a specimen 

 with 18 + 21 vertebrae and the ceratobranchial 

 filled with 12 gillrakers is a vertebral variant 

 of T. atlanticus. Although gill rakers over the 

 ceratobranchial bone can vary over a range. 



Character 



Number precaudal + caudal 

 vertebrae 



Gillraker number over cerato- 

 branchial 



First closed haemal arch 



Pterygiophore pattern 



First haemal postzygapophysis 



Shape lateral line 



Species separated 



T. atlanticus from T. thynnus, 

 T. alalunga, Thunnus spp. 



All species separable except 

 T. alalunga from Thunnus 

 spp. 



T. atlanticus + Thunnus spp. 

 from T. thynnus + T. ala- 

 lunga 



T. alalunga fromT. thynnus + 

 Thunnus spp. 



T. alalunga + T. atlanticus 

 fromT". thynnus + Thunnus 

 spp. 



T. thynnus from T. alalunga, 

 T. atlanticus, Thunnus spp. 



It is not difficult to identify specimens larger 

 than 21 mm SL. Sufficient characters are avail- 

 able and bones are well ossified and stained. How- 

 ever, variability should be taken into account and 

 characters with the least variability should be 

 relied upon the most. The number of gillrakers 

 over the ceratobranchial bone and the shape of 

 the lateral line should take precedence over the 

 other characters. I have never observed the range 

 for the number of ceratobranchial rakers in one 

 species overlap with that of another, except T. 

 alalunga with Thunnus spp., and I have never 

 seen a T. thynnus with a smoothly curved lateral 

 line. 



ACKNOWLEDGMENTS 



I express my sincere thanks to Frank J. Mather 

 III of the Woods Hole Oceanographic Institution 

 for providing the Mediterranean specimens; to the 

 staff of the Florida Department of Natural 

 Resources Marine Research Laboratory in St. 

 Petersburg and Donald P. de Sylva of the Rosen- 



586 



