188 BULLETIN OF THE BUREAU OF FISHERIES 



KEY TO GULF OF MAINE MACKERELS 



1 . The two dorsal fins are separated by a space as long as the length of the first dorsal 2 



The two dorsal fins adjoin each other or are separated by a space much shorter than 



the length of the first dorsal 3 



2. The sides below the mid line are silvery, not spotted Mackerel, p. 188 



The sides below the mid line are mottled with dusky blotches Chub mackerel, p. 209 



3. Body scaleless, except for a so-called "corselet" in the region of the shoulders 



Bonito (Gymnosarda) , p. 211 



The entire body is covered with scales 4 



4. The second dorsal fin is as high as the first or higher 5 



The second dorsal fin is lower than the first Bonito (Sarda), p. 215 



5. The anal fin is about twice as high as long; the corselet of large scales is obvious; the 



sides, are not spotted Tuna, p. 212 



The anal fin is about as long as high; there is no corselet of large scales; the sides are 

 spotted 6 



6. The anterior part of first dorsal fin is black, with the division between the dark and 



pale portions roughly vertical; about as many spots above as below the lateral line 



Spanish mackerel, p. 217 



The upper half of the first dorsal is deep blue, with the division line between the dark and 

 pale portions horizontal. Most of the spots are below the lateral line. King mackerel, p. 219 



74. Mackerel (Scomber scombrus Linnseus) 



Jordan and Evermann, 1S96-1900, p. 866. 



Description. — The mackerel is fusiform in outline, tapering rearward to a 

 very slim caudal peduncle and forward to a pointed nose. Its body is about three 

 and one-half times as long as deep, oval in section, thick, and firm-muscled as 

 are all its tribe. Its head is long (one-fourth of total length) and its mouth large, 

 gaping back to the middle of the eye (the premaxillaries are not protractile), while 

 the jaws, which are of equal length, are armed with small, slender, but very sharp 

 teeth. The eye is large, and the hollows in front of and behind it are filled with 

 the so-called ''adipose eyelid," a transparent, gelatinous mass in the form of two 

 scales, a forward and a hinder, which cover the eye except for a perpendicular 

 slit over the pupil. There are two large dorsal fins — the first triangular, originating 

 over the middle of the pectoral fin when the latter is laid back, of 10 to 14 (usually 

 11, 12, or 13) rather weak spines that can be laid down along the midline of the back 

 in a deep groove; the second, separated from the first by an interspace longer than 

 the length of the latter, is smaller (9 to 15, usually 12, rays) and is followed by 

 several small finlets, of which there are usually 5 but sometimes 4 or 6. The anal 

 is similar to the second dorsal in shape and size, originates slightly behind it, and 

 is similarly succeeded by 5 small finlets that correspond to the dorsal finlets in 

 size and shape. The caudal fin is broad, but short and deeply forked. The caudal 

 peduncle bears two small keels on either side but no median lateral keel, the absence 

 of the latter being a distinctive character. The ventral fins stand below the origin 

 of the first dorsal and like the pectorals are small. The scales of the mackerel 

 are so small that its skin is velvety to the touch; indeed,' on the belly they are 

 hardly to be seen with the naked eye, but those about the pectoral fins and shoulders 

 are somewhat larger. 



Color. — The upper surface is dark steely to greenish blue, often almost blue- 

 black on the head. The body is barred with 23 to 33 (usually 27 to 30) dark trans- 



