BERRIEN: EGGS AND EARLY LARVAE OF ATLANTIC MACKEREL 



Table 2. — Dimensions of Atlantic mackerel eggs from the cultured series and 

 plankton samples taken during May and June 1966. 



'Discrepancies between numbers of specimens in these columns are due to fractured or 

 distorted oil globules, wfiich were not measured. 



As development progresses, these pigment cells 

 become more intense and increase in number on 

 the trunk where they tend to line up in two dorso- 

 lateral rows. The lateral melanophores in the 

 thoracic region become dendritic and dense, while 

 the middorsal melanophores fade. This distinct 

 thoracic pattern persists until hatching. Melano- 

 phores appear on the anterior surface of the oil 

 globule at the same time as those on the embryo. 

 The width of the head increases to almost twice 

 that of the tail. The embryo increases in length, 

 growing past the oil globule and encircling three- 

 fourths of the egg by the end of this stage. The 

 tail twists and flexes near the oil globule until 

 it lies flat against the yolk surface. A finfold 

 begins to develop on the posterior one-third of 

 the embryo. Optic vesicles become prominent and 

 up to six myomeres are discernible. 



Late-Stage Eggs (Figure IC) 



At the start of the late stage, there are two 

 dorsolateral rows of melanophores extending back 

 from just behind the brain, well past the oil 

 globule; there are few melanophores below these 

 rows on the flanks. There is always pigment 

 on the anterior half of the oil globule, and 

 usually some on the snout and in a row behind 

 the eyes across the head. During this stage, 

 trunk melanophores migrate; they become scat- 

 tered on the flanks and in some specimens a few 

 melanophores posterior to the oil globule nearly 

 reach the ventral edge of the body by the time 

 of hatching. Pigment is lacking on the extreme 

 caudal portion of the body. Melanophores on the 

 oil globule darken and increase in number and 



coverage, so that just before hatching they are 

 scattered over most of the oil globule. As many 

 as 24 myomeres are visible prior to hatching. 

 The dorsal line of melanophores behind the eyes 

 persists on most embryos. The eyes are unpig- 

 mented through hatching. 



The embryo increases in length until it en- 

 circles the yolk, wdth the tail overlapping the head 

 just before hatching. The oil globule lies midway 

 along the body, at the posterior end of the yolk 

 sac, at hatching. The finfold deepens and extends 

 forward to occupy the posterior two-thirds of the 

 embryo. Before hatching the alimentary tract is 

 visible posterior to the oil globule and terminates 

 at the edge of the ventral finfold. 



DESCRIPTION OF LARVAE 

 Rate of Development 



Hatching occurred between 90 and 102 h after 

 fertilization at an average incubation tempera- 

 ture of 13.8°C (range 12.1° to 14.4°C). This was 

 a slightly faster rate of development than that 

 reported by Worley (1933). At this temperature 

 (13.8°C), interpolation of Worley's data would 

 indicate a time to hatching of about 120 h. The 

 yolk-sac stage ended by 137 h, for the yolk in all 

 specimens was absorbed by that time. 



Pigmentation at Hatching (Figure 2A) 



Melanophores are distributed as follows: some 

 tend to be in dorsolateral rows, extending on 

 each side from the snout over the eyes to about 

 nine-tenths of the body length, while others are 



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