FISHERY BULLETIN: VOL. 76, NO. 1 



levels were sampled or to one-half when three 

 levels were sampled. Fahay (1974) explained this 

 procedure in more detail. 



COMPARISON OF TWO SPECIES 

 OF SCOMBER LARVAE 



Scomber larvae occurred in samples from our 

 northernmost transect, off Martha's Vineyard to 

 our southernmost transect off Palm Beach. The 

 larvae were of two types, the distinction between 

 the two being more obvious in larvae smaller than 

 15 mm. One type, collected north of Cape Hat- 

 teras, predominantly over the inshore and central 

 portions of the continental shelf, during May, 

 June, and August 1966, was tentatively identified 

 as Atlantic mackerel, S. scombrus. A second type 

 collected south of Cape Hatteras was tentatively 

 identified as chub mackerel, S.japonicus. It occur- 

 red predominantly in samples taken near the 

 offshore edge of the continental shelf, during May 

 and July 1967 and January and February 1968. 

 The identities of the two types were confirmed by 

 examination of some meristic characters of the 

 large larvae and juveniles. 



Because of the similarity and possible confusion 

 of these two species, the following descriptions and 

 comparisons were compiled to facilitate future 

 identifications. Three study areas were considered 

 in larval development: meristic characters, mor- 

 phology, and pigmentation. 



Meristic Characters 



Of the 12 characters listed by Matsui (1967, 

 table 5) as distinguishing between the species of 

 Scomber, four were found to be useful in identify- 

 ing young stages dealt with here. These were: 1) 

 first-dorsal-fin spine counts; 2) counts of pre- 

 caudal and caudal vertebrae; 3) counts of first- 

 dorsal-fin ptergiophores and the arrangements in 

 relation to neural spines; and 4) the relative pos- 

 ition of the first haemal spine and the first anal 

 pterygiophore. 



Scomber japonicus has 9 or 10 first-dorsal-fin 

 spines and S. scombrus has 1 1 to 14 (Matsui 1967). 

 Examination of Formalin-preserved specimens 

 under a dissecting microscope revealed that 

 counts of 9 or 10 were attained by a length of 18.5 

 mm in S.japonicus and counts of 11 to 15 by 21.0 

 mm in S. scombrus. However, bone-stained 

 specimens of both species had higher counts and 

 earlier formation of spines than indicated in the 



above. Apparently some of the minute, posterior 

 spines in the first dorsal fin, observed in bone- 

 stained specimens, were obscured in nonstained 

 specimens by surrounding muscle and epithelial 

 tissue and by their position in the longitudinal 

 groove. I observed a complement of 10 or 1 1 spines 

 in S . japonicus as small as 11.9 mm long and 12 to 

 17 spines in S. scombrus 18.2 mm and greater 

 (Table 1). 



Counts of vertebrae were made to help identify 

 the two species of Scomber larvae. Scomber 

 japonicus is reported to have 14 precaudal and 17 

 caudal vertebrae and S. scombrus to have 13 pre- 

 caudal and 18 caudal vertebrae (Matsui 1967). 

 The first caudal vertebra is the most anterior ver- 

 tebra which has an elongate pointed haemal spine 

 and lacks ribs. In Scomber larvae the haemal 

 spine on the first caudal vertebra is noticeably 

 longer than the haemal arch on the last precaudal 

 vertebra. Also, rib articulation surfaces on haemal 

 arches of posterior precaudal vertebrae are dis- 

 tinctly flattened or truncated, rather than pointed 

 as are haemal spines on caudal vertebrae. In my 

 work counts of precaudal vertebrae were distin- 

 guishable in bone-stained S.japonicus as small as 

 7.6 mm (indeterminate at 6.7 mm) and on radio- 

 graphs by 9.3 mm. Precaudal counts characteristic 

 of S. scombrus were observable in bone-stained 

 larvae at 8.6 mm (indeterminate at 7.6 mm) and 

 on radiographs by 11.2 mm (Table 1). A few of the 

 S. scombrus specimens had precaudal and caudal 

 vertebral counts different from those reported by 

 Matsui (1967). Six of the 136 S. scombrus speci- 

 mens bone-stained or X-rayed large enough for 

 determination had 12 precaudal and 19 caudal 

 vertebrae. In two other specimens the 28th and 

 29th vertebrae were fused together, as evinced by 

 a total count of 30 and by the presence of two 

 neural and two haemal spines on the 28th ver- 

 tebra. One additional larva was observed with 

 partial fusion of the same two vertebrae. 



The numbers of first-dorsal-fin pterygiophores 

 separate the two species of Scomber. Matsui 

 (1967) reported S. japonicus has 12 to 15 first- 

 dorsal-fin pterygiophores and S. scombrus has 21 

 to 28. Full complements of pterygiophores, 13 or 

 14 in S. japonicus and 22 to 25 in S. scombrus, 

 were found in bone-stained S. japonicus as small 

 as 20.2 mm and on radiographs by 33.3 mm; they 

 were found in bone-stained S. scombrus at 32.0 

 mm and on radiographs at 38.8 mm (Table 1). 

 Because anterior pterygiophores ossify before 

 posterior ones and because there is a difference 



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