Genus Auxis Cuvier 1829 (type-species: Scomber 

 rochei Risso) by subsequent selection by Gill (1862). 



The description of the genus Auxis under "Les 

 Scombres" first appeared in Cuvier's Regne Animal in 

 1829. From the time of Cuvier's work to the present, 

 however, the genus Auxis has had several reclassifica- 

 tions. For example, in classifying the genus Auxis, Kishi- 

 nouye (1915) first included it in the family Thunnidae. 

 However, in a later work (1917), he placed Thunnidae 

 and Katsuwonidae in a new order called Plecostei and 

 placed the families Scombridae and Cybiidae in the 

 order Teleostei. The genus Thunnus fell under Thun- 

 nidae and the genera Katsuwonus. Euthynnus. and 

 Auxis came under Katsuwonidae (Kishinouye 1923). 

 The primary characteristic subcutaneous blood vessels; a 

 secondary characteristic of Plecostei was the presence of 

 well-developed subcutaneous blood vessels: a secondary 

 characteristic was the development of dark red lateral 

 tissues in relation to the subcutaneous blood vessels. 



Many scientists disagreed with Kishinouye's new 

 order and its subdivision. Takahashi (1924) argued that 

 Plecostei was established only on partial differences in 

 the highly variable vascular system and cannot exist on 

 an equal status with the other four orders of Teleo- 

 stomi. Jordan (1923) and Herre (1953) placed the 

 scombroid fishes in two families— Scombridae and 

 Thunnidae. Fraser-Brunner (19.50), on the other hand, 

 rejected any division of the family Scombridae arguing 

 that attempts to subdivide this family "have resulted in 

 arrangements which are artificial and have left the clas- 

 sification in an uneasy, shifting state.'" de Sylva 

 (1955), Collette and Gibbs (1963b), and most other re- 

 cent workers recognize a single family Scombridae with 

 various subdivisions. Collette and Chao (1975) placed 

 Auxis in the tribe Thunnini of the subfamily Scombri- 

 nae. 



The following description of the genus Auxis is from 

 Jordan and Evermann (1905): "Body oblong, plump, 

 most naked posteriorly, anteriorly covered with small 

 scales, those of the pectoral region enlarged, forming a 

 corselet; snout very short, conical, scarcely compressed; 

 mouth rather small, the jaws equal; teeth very small, 

 mostly in a single series, on the jaws only; tail very 

 slender, depressed, with a rather large keel on each side; 

 first dorsal short, separated from the second by a consi- 

 derable interspace; second dorsal and anal small, each 

 with 7 or 8 finlets; pectorals and ventrals small; no air- 

 bladder; branchiostegals 7; pyloric coeca dentritical; gill- 

 rakers very long and slender, numerous; vertebrae 39 in 

 number, peculiarly modified . . . ." 



Auxis is the most primitive genus among the higher 

 tunas that have developed a prootic pit and a partial 

 subcutaneous circulatory system (Collette and Gibbs 

 1963b). All the Thunnini, except Auxis. have a common 

 cutaneous artery that divides into dorsal and ventral 

 branches lateral to the aorta; in Auxis, however, the dor- 

 sal and ventral branches originate separately with the 

 latter being ver>' poorly developed (Collette 1978). The 

 haemal spines of the thoracic vertebrae do not form a 

 haemal arch and the first vertebra is not sutured to the 



cranium as in the higher members of Thunnini. Also, 

 compared with Euthynnus. Katsuwonus, and Thunnus, 

 Auxis lacks the frontoparietal fenestra, which is an ad- 

 ditional pair of openings present in the cranium and has 

 a lateral countercurrent system for heat exchange that is 

 not as well developed phylogenetically (Collette 1978). 

 All members of the tribe Thunnini have a swim bladder 

 as juveniles; however, the bladder degenerate with 

 growth in Auxis, Euthynnus, and Katsuwonus. 



Several other characters distinguish members of the 

 genus Auxis. the smallest of the higher tunas, from other 

 scombrids (Collette and Gibbs 1963b; Fitch and Roedel 

 1963; Williams 1963). In Auxis, there is a single interpel- 

 vic process which is between and about as long as the pel- 

 vic fins. In other tunas, but not in other scombrids, the 

 interpelvic process is bifurcate and much less than half 

 the length of the pelvic fins (it is single but small in 

 (Irammatorcynus and Gymnosarda). The number of dor- 

 sal and anal finlets (seven or eight) distinguishes Auxis 

 from .Scomber, which has only five of each. Auxis can 

 also be distinguished from Rastrelliger by the lack of a 

 corselet and a body entirely covered with moderate-sized 

 scales in the latter. 



Species — Auxis thazard (Lacepede) 1802 



The following description of A. thazard (Fig. 1, uppe^r 

 photo) is from Williams (1963). Major morphological 

 features described under the genus are omitted from the 

 account of the species. 



"Depth 3.9 to 4.5, head 3.2 to 3.8 in standard length. 

 Eye 5.0 to 5.85 in head, 1.25 to 1.66 in snout and 1.25 to 

 1.7 in the flatly rounded interorbital space. Snout 3.62 to 

 4 in head. Maxilla reaches to a point under the anterior 

 half of the eye and is 3 in head. Single row of small 

 pointed teeth in each jaw, none on palate. Jaws almost 

 equal. First and second dorsal spines subequal, equal to 

 snout and eye; following spines rapidly decreasing in 

 size, eighth usually shorter than the pupil. Second dorsal 

 fin very low, about three times its base distant from first 

 dorsal; first ray of second dorsal about 5 in head. Anal 

 similar to second dorsal, first ray about 5.2 in head. Pec- 

 torals short, roughly triangular, about 2 in head and 

 shorter than postorbital; origin of pectoral before that of 

 first dorsal. Pelvics thoracic, about 2.5 in head, origin 

 somewhat behind that of pectorals. Caudal lunate, upper 

 lobe about 1.8 in head. Body naked except for the corse- 

 let of scales anteriorly. Rear margin of the corselet runs 

 from base of second dorsal to above end of pectoral; 

 thence there is a posterior prolongation of the corselet 

 along the lateral line; below the pectoral tips the corse- 

 let margin curves to above the pelvic base from where it 

 turns posteriorly and finishes well behind the tips of the 

 pelvics. The prolongation of the corselet along the lateral 

 line tapers abruptly between first and second dorsal fins, 

 and under the origin of the second dorsal is not more than 

 4 irregular scale rows wide. Scales large and imbricated 

 above pectoral base. Gill rakers about 1.75 in length of 

 gill filaments." 



