BERRIEN: EGGS AND EARLY LARVAE OF ATLANTIC MACKEREL 



scattered on the flanks; they are found on the 

 nape; one on each side of the yolk-sac close to 

 the otocysts; and scattered on the oil globule. 

 Subsequent yolk-sac stages undergo marked 

 pigmentation changes, including the migration 

 and formation, or initial appearance of melano- 

 phores. Orton (1953) reported similar melano- 

 phore migration in Pneumatophorus japonicus 

 diego (= S. japonicus) eggs and yolk-sac larvae. 



Head Pigmentation 



Pigment on the head becomes reduced to a few 

 melanophores dorsal to the eyes and on the 

 nape (Figure 2B, C). At 66 h, pigment forms in 

 the eyes. Some specimens, between 137 and 192 h, 

 have a melanophore on the ventral midline 

 between the developing dentaries where the 

 basihyal forms. 



Abdominal Pigmentation 



Melanophores present on the oil globule at 

 hatching and at 6 h start migrating to the ven- 

 tral surface of the yolk sac by 18 h, and are most- 

 ly on that surface by 42 h. Subsequently, these 

 melanophores tend to coalesce on two areas: on 

 the forward end of the gut cavity between the 

 cleithra (Figure 2B, C) and, in some specimens, 

 on the ventral surface of the hindgut. This pig- 

 mented area on the hindgut varies in occur- 

 rence, intensity, and location. 



At 18 h, some of the melanophores which were 

 on the sides of newly hatched larvae, above the 

 middle of the yolk sac, are migrating ventrally 

 and inward above the yolk mass. By 66 h, this 

 pigment is situated over the dorsum of the midgut 

 and hindgut. Older specimens, up to 192 h, all 

 have intense or large dendritic melanophores 

 directly above the gut cavity (Figure 2C). 



Caudal Pigmentation 



The two dorsolateral rows of melanophores, 

 already somewhat scattered on the flanks at 

 hatching (Figure 2A), migrate toward the bases 

 of the dorsal and anal finfolds; this condition is 

 complete by 66 h (Figure 2B). Those melano- 

 phores at the dorsal finfold base decrease to about 

 6 by 192 h and are located on the posterior half 

 of the larva; those in the ventral row increase 

 to about 20 to 25 and extend from near the vent 

 back to the caudal extremity, exclusive of finfold. 



Myomeres 



At 102 h, only 23 or 24 myomeres were ob- 

 served in the unhatched eggs. Others most cer- 

 tainly present were obscured by the opacity of 

 the yolk. In the newly hatched larvae, however, 

 the full complement of 31 myomeres was evident. 



Finfold 



In newly hatched larvae, a continuous finfold 

 extends posteriorly on the dorsal surface from 

 slightly behind the auditory vesicle, around the 

 caudal extreme, then forward on the ventral 

 surface to the yolk sac. The finfold broadens, 

 lengthens, and reaches the top of the head by 

 66 h where it persists to 192 h. With develop- 

 ment, the ventral finfold extends forward to the 

 anus, and as the yolk sac decreases in length the 

 preanal finfold occupies the area between the anus 

 and yolk sac. Actinotrichia are barely visible in 

 the caudal portion of the finfold on newly hatched 

 larvae and become more evident on older stages 

 (Figure 2). 



Alimentary Canal 



The hindgut, observable in the ventral finfold 

 of larvae at hatching as a narrow tract, is much 

 thickened at 18 h. Mouth rudiments are present 

 on 66-h larvae, and by 137 h, when the yolk 

 material is completely absorbed, the mouth is 

 open. A pair of recurved teeth occur on each jaw 

 at 192 h (Figure 2C). 



Otocysts 



The otocysts are visible at hatching. Develop- 

 ing otoliths are barely visible at 42 h and are 

 plainly evident by 66 h (Figure 2). 



Pectoral Buds 



The newly hatched larvae have pectoral buds. 

 By 66 h, these buds have fleshy bases, fan-shape 

 membranes, and appear functional (Figure 2 A, B). 



SUMMARY 



For identification purposes, it is useful to 

 summarize some of the more prominent features 

 of Atlantic mackerel eggs and early larvae. The 



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