SILVER MULLET 



401 



YOLK-SAC LARVAE 



Hatching: began 40 hours after fertilization, and 

 no increase in number of larvae was evident after 

 42 hours. The larvae floated at the surface, and 

 movement consisted lar^jely of occasional jerking 

 actions. Only 3 newly hatched larvae were 

 preserved, and these had a size range of 1.63 to 

 1.76 mm. total length, and an average of 1.69 mm. 

 The larae hatch in an undeveloped state, 

 lacking a mouth and fins, and without pigment in 

 the eyes (fig. 3). The large oil globule is 

 located, in a large part, in the posterior half of 

 the yolk sac. Pigmentation consists of ventral 

 rows of pigment spots, in addition to the dorsal 

 rows, and a few scattered melanophores on the 

 sides of the body and head. 



Four hours after hatching (fig. 4) the body had 

 lengthened (11 specimens ranged in total length 

 from 1.74 to 2.15 mm., an average of 1.89 mm.) 

 and there was considerable shrinking of the yolk 

 mass; the finfold was more developed and begin- 

 ning to constrict in the caudal region. Pigmenta- 

 tion remained essentially the same. At 16 hours 

 (fig. 5) there was a further increase in length (7 

 specimens ranged in total length from 2.30 to 

 2.47 mm., an average of 2.36 mm.), the yolk mass 

 was much reduced, the finfold had reached its 

 ma.ximum development, and no basic change in 

 pigmentation had occured. 



The larvae were dying rapidly after 32 hours, 

 and it was apparent none would survive much 

 longer. Consequently 6 of the more active ones 

 were preserved at this stage (ranging in total 

 length from 2.49 to 2.68 mm. and averaging 2.56 

 mm.). Other than this increase in length, a 

 smaller yolk mass, and minute pectoral fin buds; 

 tliese larvae were similar to those at 16 hours 

 after hatching, and are not figured. 



All larvae were dead 45 hours after liatching, 

 and the last to die appeared to have been infected 



by fungus. For this reason I have not considered 

 specimens older than 32 hours. The develop- 

 mental series is continued with material from 

 [)lankton tows. 



Two specimens from the plankton material, 

 both 2.56 mm. total length and from the same tow! 

 indicate that the yolk-sac larva begins a rapid 

 transition at about 2.5 mm. total length. In the 

 least developed of the specimens (fig. 6), the larval 

 hump has disappeared and small pectoral buds 

 are evident. The oil globule has shrunk, but 

 remains comparatively large, and the yolk mass 

 has decreased. The mouth is not diflFerentiated, 

 and the eyes have no pigment. Body pigmenta- 

 tion remains essentially the same, irregular 

 dorsal and ventral rows of pigment spots with a 

 few scattered melanophores on body and head. 

 The finfold is more constricted in the caudal 

 region. The second 2.56-mm. specimen (fig. 7) 

 has a distinct head, and the mouth has developed. 

 The eyes are pigmented, and tlie pectoral fin has 

 enlarged into a fleshy-based, fan-shaped fin 



FiGCRE 4.— Yolk-sac larva, 2.15 nir 



FiGCRE 5.— Yolk-sac larva, 2.47 mm. 



FiGi RE 6. — Yolk-sac larva, 2.5(1 mm. 



FiGCRE 3.— Xi'wly liatclicd larva, 1.7C> mm. 

 4-.>:n82 0— 57 2 



FiGLRE 7.— Yolk-sac larva, 2.56 mm. 



