SILVER MULLET 



399 



Soine collections to supplement the material 

 and (lata collected with the MA' Theodore N. GUI 

 in offshore waters have been made on a semi- 

 monthly basis since 1953 at three localities in 

 Georgia. One station is on the open ocean beach 

 on St. Simons Island, a second is in the marshy 

 estuarine area behind the barrier islands, and the 

 third is up the Altamaha River at about tidewater 

 limits. Oidy beach and marsh material are in- 

 cluded in this paper. 



All descriptions of eggs, larvae, and juveniles 

 are based on preserved material urdess otherwise 

 stated. 



Measurements of eggs and the larvae up to about 

 25 mm. in length were made with a stereoscopic 

 microscope and a micrometer eyepiece. The 

 larger specimens were measured with calipers. 



Both standard lengths (in small specimens from 

 the tip of the snout to tip of the urostyle) and total 

 lengths (in small specimens from the tip of the 

 snout to tip of the finfold or caudal fin) were 

 determined. For discussions of body proportions 

 only standard lengths were used. In other dis- 

 cussions, larvae less than 7.0 mm. standard length 

 are referred to in total lengths, and those 7.0 mm. 

 and larger in standard lengths (figs. 3 through 16 

 follow this procedure). 



Original measurements were used to construct 

 the curves portraying rates of growth of various 

 body parts, and changes in certain body propor- 

 tions. 



I have followed the general approach used by 

 Ahlstrom and Ball (1954) in presenting the larval 

 development in that sequences of fin formation, 

 body proportions, and pigmentation are discussed. 

 Egg development and yolk-sac larvae are pre- 

 sented separately. 



DEVELOPMENT OF THE EGG 



The pelagic eggs of the silver mullet are splieri- 

 cal in shape and contain single, large oil globules. 

 In unfertilized eggs (fig. 2a) the yolk appears as 

 an unsegmented opaque mass with little, if any, 

 perivitelline space. The oil globule is pale yellow 

 and located at the top of the yolk mass. The 

 surface of the eggshell has a finely scratched or 

 etched appearance. A series of 10 unfertilized 

 eggs ranged in diameter from 0.77 to 0.86 mm., 

 witli an average of 0.82 mm.; and tlic diameter of 



the oil globules ranged from 0.27 to 0.32 mm., 

 with an average of 0.30 mm. 



Two hours after fertilization (fig. 2b) the eggs 

 had reached the 32-blastomere stage and had 

 developed a perivitelline space ranging from 0.04 

 to 0.12 mm. wide. A series of 10 eggs at this 

 stage ranged in diameter from 0.86 to 0.92 mm., 

 with an average of 0.90 mm.; and had oil globules 

 with diameters ranging from 0.27 to 0.32 mm. 

 and averaging 0.30 mm. The small increase in 

 average diameter of the egg appears to result 

 from absorption of water with an accompanying 

 expansion of the eggshell and development of the 

 perivitelline space. From this stage of develop- 

 ment until hatching the diameters of the eggs and 

 oil globules maintain about the same range of 

 sizes and averages. The perivitelline space and 

 yolk mass vary as the embryo develops and some 

 of the yolk material is used up (fig. 2, c to i). 



Four hours after fertilization (fig. 2c) the blasto- 

 disc was well formed and berrylike in appearance. 

 The segmentation cavity was present 8 hours 

 after fertilization (fig. 2d), and the embryonic 

 shield was well advanced in 12 hours (fig. 2e). 



The embryo was well differentiated 16 hours 

 after fertilization (fig. 2f). The optical vesicles 

 are well defined, eight somites are visible, and 

 the blastopore is closed. The tail has not begun 

 to separate from the yolk, which at this =tage has 

 a granular appearance. Irregular lines of pig- 

 ment spots are present on the dorsal surface of 

 the embryo, one on each side of the notochord, 

 extending from just behind the head onto the tail 

 section. 



At 24 hours after fertilization (fig. 2, g, h) 

 pupils have developed in the large eyes, 24 myo- 

 meres are discernible, and the tail has started to 

 separate from the yolk mass which remains 

 granular in appearance. Melanophores in the 

 rows of pigment spots, on the dorsal surface of the 

 embryo (one row each side of center line) are now 

 more closely set and extend from just back of the 

 eyes to that portion of the tail which is free from 

 the yolk mass. A few scattered melanophores 

 appear on the sides of the embryo. 



After 32 hours (fig. 2i) the embryo has a well- 

 developed finfold and the tail free for about one- 

 third the length of tiie body. In addition to the 

 dorsal rows of pigment spots, melanophores are 

 present on the ventral aspect of the embryo and 

 are more numerous on the sides of the bodv. 



