14 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 7. Examples of features of yolk-sac larvae of teleosts. (A-C). Paracallionymus costatus. A. soon after hatching 0.98 mm NL; B. 1.8 mm 

 NL; C. 1.9 mm NL. From Brownell (1979). Features demonstrated in; (A) include the small size of the larva, the lack of an oil globule, the 

 segmented yolk, and the dorsally arranged melanophores; (B) demonstrates the migration of melanophores ventrally and the formation of the 

 anus producing a preanal finfold; (C) demonstrates further ventral migration of melanophores, beginning of larval pectoral fin formation, the 

 decrease in yolk-sac size, and beginning of pigment in the eye; (D) Diplodus sargus. 2.4 mm NL. From Brownell (1979). Single pigmented oil 

 globule posterior in the unsegmented yolk and a short preanal finfold are demonstrated; (E) Trachurus I. capensis. 2.2 mm NL. From Brownell 

 (1979). Single pigmented oil globule anterior in segmented yolk with moderately long preanal finfold demonstrated; (F) Cololabis saira. 5.1 mm 

 SL. (original). Well-developed, heavily pigmented yolk-sac larva at hatching with notochord flexion beginning and some caudal rays formed; (G) 

 Argentina silus. 1.1 mm. Redrawn from Schmidt (1906c). A large but poorly developed yolk-sac larva at hatching with a large oil globule; and 

 (H) Hippoglossus slenolepis. 9.5 mm. From Pertseva-Ostroumova (1961). A large but poorly developed yolk-sac larva at hatching with no oil 

 globule. 



its. As mentioned earlier, at hatching, particularly in marine 

 fishes with pelagic eggs, the fish is in an extremely undeveloped 

 state and then, as a free-living individual, it gradually develops 

 the adult characters. This process is continuous, but there are 

 morphological and ecological mileposts that are significant in 

 the life of the fish and which allow us to subdivide this process 

 so that we can communicate results of our studies and compare 

 different fishes at the same moment in development. 



Fish early life history has been and continues to be studied 

 from a number of different perspectives (Ahlstrom and Moser, 

 1976). Some studies deal directly with embryology and later 

 ontogeny, others emphasize functional morphology of larval 

 structures, apply larval features to taxonomic and systematic 

 studies, investigate the ecology of eggs and larvae, or use these 

 stages to address fishery-related problems such as assessment 

 of spawning stock size and recruitment success. All of these 



studies have in common the need to subdivide early life history 

 and communicate information based on processes and events 

 occurring during these subdivisions. As with any communica- 

 tion, it is vitally important to use terms that are clearly defined 

 and this is particularly true with the diverse disciplines that are 

 involved in larval fish studies. Historically, several disciplines 

 have used different names for the same stage, or subdivided 

 development differently [see Okiyama (1979a) and Fig. 6 in this 

 paper]. This has led to confusion rather than communication. 

 Several criteria seem appropriate for defining stages of de- 

 velopment to be used by students of any discipline. The variety 

 of developmental patterns should be recognized and the defi- 

 nitions should apply to as many patterns as possible. Thus, 

 stages should be based on very widespread, fundamental fea- 

 tures of development. The stages should have some significance 

 in the life history of the fish, both morphologically and func- 



