18 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



,r ..'—v ^„.-«n.-)-'-T' ^ 









Fig. 9. Examples of teleost larvae illustrating extremes of some systematically useful larval characters. (A) Myctophum aurolaternatum. 26.0 

 mm (Moser and Ahlstrom, 1974). Note stalked oval eye with choroid tissue, trailing gut, and dorsal fin developing in finfold; (B) Epinephelus 

 sp.. 8.4 mm (Kendall, 1979). Note elongate, serrate dorsal and pelvic spines; (C) Adioryx (Holocentrus) vexillarius. 8.5 mm (McKenney, 1959). 

 Note head spines; and (D) Lopholatilus chamaeleonticeps, 6.0 mm (Fahay and Berrien, 1981). Note spines on head and body. 



crest and are generally aligned along the dorsal surface of the 

 embryo. During the yolk-sac stage, these melanophores move 

 laterally and ventrally to establish the beginning of the larval 

 pigment pattern. Orton (1953a) describes these events in detail 

 in Sardinops sagax. This realignment may begin during the late 

 embryonic stages, before hatching. Some species hatch with few 

 if any melanophores, and when they first appear, they are in 

 ventral positions. Apparently, the pigment cells migrate before 

 pigment formation occurs. 



The presence and position of oil globules in yolk-sac larvae 

 vary and can be of diagnostic value. In fishes with single oil 

 globules, it can be far forward (e.g., labrids, most carangids, 

 muUids, and lethrinids), in the middle of the yolk sac (e.g.. some 

 clupeids, serranids, and argentinids), or more usually near the 



rear of the yolk sac. The shape and relative size of the yolk sac 

 itself are variable and provide additional taxonomic characters. 

 In summary, although the yolk-sac stage starts at hatching 

 and ends when the yolk is absorbed, fish are at different stages 

 of development with regard to such features as pigmentation, 

 eye development, and fin formation during this stage. The strik- 

 ing pigment rearrangements that occur during this stage provide 

 further emphasis that the yolk-sac stage is a transitional stage 

 between the egg and larval stages. 



The Larval Stage 



During the larval stage many ontogenetic changes occur (Mos- 

 er. 1981). Some of these relate directly to the development of 

 the adult form while other changes and structures are specialized 



