FABLE ET AL.; DESCRIPTION OF EGGS AND LARVAE OF SPOTTED SEATROUT 



Middle Stage Eggs 



Duration of the middle stage is about 4 h. At 9 h 

 after fertilization, the notochord develops further 

 and the forebrain begins to develop. Small mel- 

 anophores are present for the first time around the 

 optic vesicles and in no apparent pattern along the 

 body. In the 10th hour, six to eight myomeres can 

 be seen with difficulty on the posterior one-third of 

 the embryo. By the 12th hour, the embryo extends 

 over about one-half the circumference of the egg. 



Late Stage Eggs 



The tip of the tail of the embryo has separated 

 from the yolk and the finfold is evident on both the 

 posterior dorsal and ventral caudal regions at 13 

 h. Eighteen to 20 myomeres are present. Melano- 

 phores, which are present over the entire body of 

 the embryo, are concentrated around the dorsal 

 surfaces of the eyes, on either side of the 

 notochord, and along the base of the finfold. At 15 

 h (Figure lA), the tail of the embryo is well past 

 the oil globule and has developed a marked curve. 

 The finfold surrounds the posterior half of the 

 embryo and 24 to 25 myomeres can be counted. 

 Internal organs show some differentiation, while 

 anteriorly the eyes are pronounced and the hind- 

 brain is developing. One hour later, the embryo 

 occupies three-fourths of the circumference of the 

 egg. Twenty-five myomeres are apparent. 



Hatching occurs 16 to 20 h after fertilization, 

 when incubation temperatures are approximately 

 25°C. In other experiments, hatching occurred in 

 15 h at 27 °C and in 21 h at 23 T. 



LARVAL DEVELOPMENT 



Hatching (Figure IB) 



Standard lengths of 20 newly hatched larvae 

 ranged from 1.30 to 1.56 mm and averaged 1.46 

 mm. At hatching the oil globule is located at the 

 posterior end of the yolk sac. Some scattered 

 melanophores like those in the embryos are still 

 found, but most are indistinct, especially those 

 along the finfold. No pigment is visible in the yolk 

 or on the oil globule. 



Sixteen Hours Posthatching (Figure 2A) 



At 16 h, larval standard lengths ranged from 

 1.89 to 2.10 mm and averaged 2.03 mm. The finfold 



is large and clear with no fin differentiation. The 

 mouth is undeveloped, only a little yolk remains, 

 and the oil globule is still in a posterior position. 

 Otocysts are faintly visible within the otic cap- 

 sule. Pectoral fin buds are evident for the first 

 time. The alimentary canal is straight, terminat- 

 ing at the anus in the anterior half of the body. 



Body pigments are in four vertical bands located 

 above the abdomen, above the anus, and one-third 

 and two-thirds of the distance from the anus to the 

 tip of the notochord. Small melanophores are con- 

 centrated in these bands, but many disappear with 

 preservation. The most prominent of the bands is 

 located one-third of the way from the anus to the 

 notochord tip. Pigmentation in preserved speci- 

 mens is most distinctive in the head region. Sev- 

 eral small dendritic melanophores are located 

 above and behind the eye. Two dendritic melano- 

 phores are located on the dorsomedial surface of 

 the head. Some slight black pigmentation is visi- 

 ble above the abdomen where the first pigment 

 band is located. Numerous granular melano- 

 phores are also found on the finfold at the dorsal 

 and ventral body margins at the notochord tip. 



Forty Hours Posthatching 



At 40 h, the larvae average 2.10 mm SL, the 

 mouth is formed, and the yolk sac is almost com- 

 pletely gone. The head has grown very deep, and 

 the brain appears dorsally over the eyes. In pre- 

 served fish the eye is totally black, and pectoral 

 fins stand out from the sides. Internal organs are 

 increasing in size and complexity, but the alimen- 

 tary canal is still straight, although thicker than 

 at hour 16. 



Pigmentation undergoes distinctive changes 

 prior to 40 h of age. The four vertical bands which 

 occur on the 16-h larva are absent, and only one 

 wide, diffuse band is found just forward of the 

 half-way point between the anus and the tip of the 

 notochord. Melanophores are intensifying along 

 the dorsal and ventral body margins within the 

 band and anteriorly over the abdomen. The granu- 

 lar melanophores on the finfold at the tip of the 

 notochord are somewhat fewer in number. Dendri- 

 tic melanophores are on the dorsal surface of the 

 abdomen. Pigmentation on the lower jaw is 

 heaviest at the angle and posteriorly. A few small 

 melanophores are anterior to this and at the tip of 

 the lower jaw. 



The pigment which remains least distinct and 

 disappears after a short period in Formalin is that 



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