BAIRDIELLA CHRYSURA AND ANCHOVIA MITCHILLI. 



II 



During the following day the larval fishes do not increase in size materially. They 

 undergo material changes in form and color, however. At two days after hatching 

 (fig. 19) they remain 2.5 to 2.8 mm. in length. The yolk is completely absorbed. 

 The depth of the head is now greater than the depth of the body. The fin folds remain 

 continuous and the depth of each fold remains greater than the depth of the body 

 posterior to the vent. The general color of the body is light brownish yellow, marked 

 by two distinct vertical bands. The anterior vertical band is located just posterior to 

 the head. It is composed of yellow chromatophores on a blackish background. The 

 general macroscopic _ 



Fig. 19. — Bairdiella chrysura. Larval fish 2 days after hatching, actual length 3.6 mm. 



effect of this band is 

 blackish. The posterior 

 vertical band is located 

 approximately two- 

 thirds the distance from 

 the vent to the posterior 

 end of the body. It is 

 composed of a dorsal and 

 a ventral group of yellow chromatophores on a diffuse blackish background. The macro- 

 scopic effect of this band is yellowish. Yellow chromatophores no longer appear on other 

 parts of the body. The fin folds and the posterior end of the body remain transparent. 

 The critical period for these larvae begins during the third day after hatching. 

 When kept in dishes of sea water they began at this time to die rapidly. Few survived 

 until the fourth day. Means of keeping the larvae alive for a longer period was not 

 available. Observations on the later larval development, therefore, were made on 

 larval fishes taken alive in the stow net. 



After the critical period is passed the little fishes feed actively and probably grow 

 comparatively rapidly. Figure 20 illustrates a young fish 3.5 mm. in length. The 



relative depth of 

 the body in fishes 

 of this size is mate- 

 rially greater and 

 the trunk tapers 

 more rapidly 

 toward the poste- 

 rior end than in 

 larvae which have 

 not yet passed the 



critical period. The posterior end of the notochord is slightly elevated. The 

 posterior end of the body is asymmetrical and betrays an ancestral heterocercal con- 

 dition of the tail. The fin folds remain continuous. The depth of each fold is now 

 less than the depth of the body posterior to the vent. The general color of the body is 

 somewhat lighter than in the earlier larvae. Both. vertical bands are distinctly blackish. 

 Yellow pigment is still present in the vertical bands, but is obscured by the denser 

 blackish ground color. From the anterior vertical band two blackish bands extend 

 antero-ventrally. One of these blackish bands terminates in proximity with the eye, 

 the other extends diagonally over the preopercle and cheek. The posterior vertical 





-*"...*,.*...*.:. 





Fig. 



-Bairdiella chrysura. Larval fish 3.5 mm. in length. 



