FISHERY BULLETIN; VOL. 76, NO. 1 



the time of spawning until hatching. Larvae de- 

 scribed in this report were from eggs spawned on 7 

 October 1975 and were transferred to rearing 

 aquaria. Samples of larvae were preserved daily in 

 Wc Formalin for 15 days. 



Larvae were reared in 57-1 aquaria which were 

 filled with algae and rotifer culture water 2 days 

 prior to the introduction offish. Algal growth was 

 enhanced by a constant light source above the 

 aquaria. Seatrout were fed the rotifer, Brachionis 

 plicatilis, daily at a rate of at least 20/ml of water 

 for 4 days. On the fifth day rotifers and brine 

 shrimp, Artemia sp., nauplii (3-5/ml) were both 

 introduced. This combination was fed until larvae 

 were 8 days old, then brine shrimp were used as 

 the only food source. Temperatures in the aquaria 

 were maintained at 24.0° to 26.0°C. 



Eggs and larva were measured using an ocular 

 micrometer in a dissecting microscope. Measure- 

 ments included total length, standard length, 

 snout to anus length, snout length, head length, 

 eye diameter, and body depth. Illustrations are of 

 preserved specimens. In discussing seatrout eggs, 

 the three stages described by Ahlstrom and Ball 

 (1954) are used. 



EMBRYONIC DEVELOPMENT 



Spotted seatrout eggs are pelagic and spherical, 

 the chorion is clear and unsculptured, and the yolk 

 is homogeneous. The perivitelline space in live 

 eggs is narrow, occupying approximately 4% of the 

 egg diameter. One hundred live eggs and 100 

 Formalin-preserved eggs were measured at vari- 

 ous stages of development. No differences in 

 diameters of eggs or oil globules were noted at 

 different stages of development. Diameters of both 

 live and preserved eggs averaged 0.77 mm. The 

 diameter of live eggs ranged from 0.73 to 0.82 mm 

 while diameters of preserved eggs ranged from 

 0.70 to 0.85 mm. 



The eggs usually contain one yellow oil globule, 

 but some eggs (2% ) have two or three globules. Oil 

 globules in preserved eggs range from 0.18 to 0.26 

 mm in diameter, with a mean of 0.22 mm. Oil 

 globules in live eggs range from 0.22 to 0.27 mm in 

 diameter, with a mean of 0.23 mm. When more 

 than one globule is present, sizes vary greatly. 



Early Stage Eggs 



Duration of the early stage is about 8 h. Eggs 

 preserved in Formalin have yellowish oil globules. 



opaque cells, and, in this early stage, a shrunken 

 and disorganized yolk (possibly due to poor pre- 

 servation). Eggs float with the oil globule(s) on top 

 and the developing cells on the bottom. 



Development proceeds as follows: IV2 h, 16- or 

 32-cell stage; 2 h, morula stage; 3 h, blastula stage; 

 4 h, gastrulation begins; 6 h, gastrula encircles 

 two-thirds of the yolk and primitive streak is evi- 

 dent; 8 h, blastopore closure. At the onset of gas- 

 trulation, numerous small droplets form around 

 the oil globule. By blastopore closure, optic vesi- 

 cles are visible in most eggs and the notochord can 

 be seen in some. Myomeres are not discernable 

 and no pigmentation is present on the egg or em- 

 bryo. 



0.5 mm 



1.0mm 



Figure 1 . — Spotted seatrout embryos: A) 15 h after fertilization; 

 B) at hatching (SL 1.46 mm). 



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