FISHERY BULLETIN: VOL. 73, NO. 1 



FiGURK 1. — Atlantic mackerel eggs: A, early stages; B, middle 

 stage; C, late stage. 



Perivitelline Space 



In live eggs, the perivitelline space occupies 

 about one-twentieth of the eggshell diameter, or 



about 0.05 mm. The eggs illustrated (Figure 1) 

 are idealized only to the extent that the width 

 of perivitelline space conforms to the observations 

 on live eggs. 



Pigmentation 



Two large yellow chromatophores were ob- 

 served in the live eggs at 60 and 85 h after fer- 

 tilization. These chromatophores were situated 

 on either side of the embryo immediately behind 

 the head. No further notes on chromatophores 

 of this color were kept. By the time I observed 

 the eggs and larvae, several months after pres- 

 ervation, only melanophores were observed. 

 All further comments on pigmentation refer to 

 melanophores. 



Development 



Following the criteria of Ahlstrom and Ball 

 (1954), this paper describes the development of 

 the Atlantic mackerel egg in three stages: early 

 (fertilization to closure of the blastopore), middle 

 (blastopore closure to the twdsting of the tail), 

 and late (tail twisting to hatching). The early 

 stage terminated shortly after 36 h, as the 

 blastopore was 0.3 mm across at that time; the 

 middle stage was completed by 72 h, when the 

 tail was observed twisted; and the late stage 

 lasted till hatching, by 102 h after fertilization. 

 Incubation temperature ranges of the three stages 

 were: early, 12.1° to 14.4°C; middle, 13.8° to 

 14.2°C; and late, 14.1° to 14.2°C. 



Early-Stage Eggs (Figure lA) 



Early-stage Atlantic mackerel eggs are char- 

 acterized by the dimensions given above and by 

 the presence of a single yellow oil globule. The 

 oil globule is off-center at the vegetal pole, 

 opposite the blastodisc at first and, with develop- 

 ment of the embryo, slightly posterior to the tail 

 at the time of blastopore closure. There are no 

 visible myomeres, pigmentation, or formed eyes. 



Middle-Stage Eggs (Figure IB) 



Soon after the blastopore closes, pigmentation 

 becomes visible on the embryo as numerous, 

 scattered fine points on the dorsal surface of the 

 thoracic region and a few back along the trunk. 



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