WATSON: DEVELOPMENT OF EGOS AND LARVAE OF WHITE CROAKER 



or two melanophores may overlie the gut at the 

 level of the soon-to-inflate swim bladder at myo- 

 meres 1 and 2. 



Morphology 



Genyonemus lineatus larvae hatch in a rela- 

 tively undifferentiated state with unpigmented 

 eyes, otic capsules usually with sagittae, a func- 

 tional but simple tubular heart, straight tubular 

 gut, large yolk sac, and posterior oil droplet. No 

 mouth, branchial apparatus, or other viscera are 

 apparent. 



Pectoral buds appear during the second day 

 after hatching and pectoral membranes are 

 present on the third. The mouth opens and the 

 operculum becomes discernible during the third 

 day. Gut differentiation begins at this time. Yolk 

 exhaustion and swim bladder inflation occur on 

 the sixth day. Feeding, and consequently the end 

 of the yolk-sac stage, is initiated during the sixth 

 or seventh day after hatching (at ca. 13°-14°C). 



Larvae lengthen during the yolk-sac stage, 

 from a preserved hatching length of 1.57 mm (n 

 = 4, SD = 0.02 mm) to 2.41 mm (n = 4, SD = 0.02 

 mm) at yolk exhaustion. Yolk-sac length declines 

 from 0.86 mm (n = 4, SD = 0.04 mm) at hatching 

 to zero. Head length, preanal length, and eye 

 diameter change little during the yolk-sac 

 stage. 



LARVAE 



Pigmentation 



Genyonemus lineatus larvae are quite variable 

 in degree of pigmentation (e.g., midwinter lar- 

 vae often are more lightly pigmented than 

 spring larvae), although the basic pattern is con- 

 servative. Because of this variability, pigmenta- 

 tion is described more fully than might other- 

 wise be warranted. Illustrations are of typical 

 (i.e., late winter) specimens. 



The head typically is moderately pigmented at 

 the beginning of the larval stage (Fig. 4a). Single 

 small melanophores are nearly always present 

 on the snout and at the angular bone, as many as 

 four or five may be scattered over the fore- and 

 midbrain regions, and one or two are often lo- 

 cated in the floor of the otic capsule. Some speci- 

 mens have an elongate melanophore laterally on 

 the mandible. 



The snout melanophore is lost soon after yolk 

 absorption and the snout remains unpigmented 



throughout larval development. Small melano- 

 phores begin to appear between the nostrils at ca. 

 17 mm and rapidly proliferate to form a band 

 which persists until becoming obscured by the 

 increasing head pigmentation in the juvenile 

 stage. 



The melanophore at the angular bone persists 

 through the juvenile stage. Mandibular pigment 

 typically is absent until the beginning of transi- 

 tion at ca. 13 mm, when a pair of melanophores 

 appears at the center of the mandible. The num- 

 ber increases to six or eight by the beginning of 

 the juvenile stage (ca. 17 mm). Premaxillary pig- 

 mentation begins shortly before transition, with 

 a pair of melanophores at the center of the upper 

 jaw. Four to six more melanophores are added by 

 the beginning of the juvenile stage. Some small 

 specimens may have one or two melanophores in 

 the central gular region. These rarely persist 

 beyond ca. 5 mm. 



Pigment on top of the head declines rapidly 

 early in the larval stage, and is absent after ca. 

 2.8 mm. During the transitional period melano- 

 phores again appear on the head, beginning with 

 a pair over the midbrain region at ca. 14.8 mm. 

 Melanophores rapidly proliferate to form bands 

 over the midbrain by the beginning of the juve- 

 nile stage. 



Opercular pigmentation is acquired just be- 

 fore the juvenile stage, with a pair of melano- 

 phores under the central opercular region. One 

 or two external melanophores develop on the 

 upper operculum at ca. 17.2 mm and quickly in- 

 crease in number to form a dark patch. 



Otic floor pigment is most often present in lar- 

 vae <4 mm and absent in larger specimens. At 

 ca. 9.5 mm a melanophore appears under the 

 anterior hindbrain, followed by an anterolateral 

 melanophore on each side at ca. 10 mm. A second 

 ventrolateral melanophore is acquired here dur- 

 ing transition (ca. 13 mm) and by the beginning 

 of the juvenile stage the anterior hindbrain is 

 usually surrounded by a heavy pigment band. 



At the beginning of the larval stage dorsal 

 trunk pigment includes one or two nape-finfold 

 melanophores, usually a single middorsal me- 

 lanophore between myomeres 16 and 18, often a 

 middorsal or dorsolateral melanophore between 

 myomeres 6 and 8, and occasionally one or two 

 small middorsal melanophores near the tip of the 

 notochord (Fig. 4a). Lateral trunk pigment 

 which persists into the larval stage is located at 

 myomeres 6-8 and 16-18. This usually is lost by 

 2.8 mm although an occasional specimen of any 



407 



