FISHES OF THE GULF OF MAINE 



339 



Figure 181. — Tuna (Thunnus thynnus). After Smitt. 



large number of finlets) sufficient in itself to sep- 

 arate a very young one from either of our true 

 mackerels. A small one is readily separable from 

 the striped bonito and from the false albacore by 

 the fact that the entire trunk of the tuna, includ- 

 ing the belly, is scaly, the upper outline of its 

 first dorsal fin only very slightly concave; and 

 from the common bonito (p. 337) by a second 

 dorsal that is considerably higher than it is long 

 by the shape of its anal with only weakly con- 

 cave margin, by the small size of its jaw teeth; 

 and by the midline of the roof of its mouth armed 

 with hairlike teeth. The plain coloration of the 

 tuna, without dark markings, is still another con- 

 venient field mark for separating small ones from 

 any of the bonito tribe that have been reported 

 from our Gulf. 



The tuna is shaped like a bonito rather than 

 like a mackerel, with robust body, about one- 

 fourth to one-sixth as deep as long, tapering to a 

 pointed nose and to a very slender caudal pe- 

 duncle which bears a strong median longitudinal 

 keel on either side. The first dorsal fin (13 or 14 

 spines), originating close behind the axil of the 

 pectoral, is triangular, its upper edge weakly con- 

 cave, tapering backward from its first spine, and 

 with the last spine very short indeed. And it can 

 be laid down, flush, in a groove along the back. 

 The second dorsal (about 13 rays, not depressible) 

 is almost confluent with the first (a little lower 

 than the latter in young fish and a little higher in 

 old) is at least as high as it is long or higher, 

 deeply concave behind, and with sharp-pointed 

 apex. The anal fin originates under the rear end 

 of the second dorsal to which it is similar in out- 



line and size (about 12 rays). Usually there are 

 9 or 10 dorsal finlets and 8 or 9 anal finlets, 

 behind the second dorsal fin and the anal fin, 

 respectively. The tail fin is much broader than 

 long, its margin evenly lunate, its two lobes sharp 

 pointed, much as it is in the bonitos. The pec- 

 toral and ventral fins are of moderate size, the 

 former scimitar-shaped and much longer than 

 broad. 90 



Color. — The back is dark lustrous steel blue or 

 nearly black, with gray or green reflections; the 

 cheeks silvery; the sides and belly silvery gray, 

 often with large silvery spots and bands, and 

 iridescent with pink. The first dorsal is dusky 

 to blackish; the second dusky to reddish brown; 

 the dorsal finlets yellow with dark edgings. The 

 anal fin is silvery gray; the anal finlets the same, 

 or yellow; the caudal dusky but more or less 

 silvery; the ventrals and pectorals blackish above 

 and silvery gray below. 81 



Size. — This is the largest Gulf of Maine fish, 

 except for some sharks; a length of 14 feet or 

 more, and a weight of 1,600 pounds being rumored, 

 with fish of 1,000 pounds not rare. The heaviest 

 Rhode Island fish on record, taken about 1913, 

 weighed 1,225 pounds, while 4 or 5 fish have been 

 brought into Boston that weighed approximately 



» The tunas and their allies are discussed by Jordan and Evermann (Occas. 

 Papers, Cal. Acad. Sci. vol. 12, 1926); Fraser-Brunner (Annals and Maga- 

 zine Nat. Hist., Ser. 12, vol. 3, 1950, pp. 142-146) has recently given a con- 

 venient key to all known species of tunas, with excellent illustrations; and 

 Godsil and Holmberg have recently discussed the relationships of the blue- 

 fin tunas of New England, Australia, and California (Fish. Bull. 77, Cali- 

 fornia Dept. Nat. Resources, 1960). 



•' The foregoing description of the color is based on accounts of freshly 

 caught tuna by Storer (Fishes of Massachusetts, 1867, p. 65) and by Nichols 

 (Copeia, No. Ill, 1922, pp. 73-74); and on fish we have seen. 



