KENDALL ET AL.: ELH STAGES AND CHARACTERS 



15 



From demersal eggs 



From pelagic eggs 



Clupea harengus harengus 



egg diameter = 1.2-1. 5mm 

 NL at hatclning = 4.9mm 



Etrumeus teres 

 egg diameter = 1.3mm 

 NL at hatching = 4.8mm 



Krevanoski 1956 



Mito 1961 



O 



Mukhacheva and Zviagina 1960 



Gadus macrocephalus 



egg diameter = 0.8-1. 4mm 

 NL at hatching = 3.6mm 



Colton and IWarak 1961 



Gadus morhua 

 egg diameter = 1.1 -1.9mm 

 NL at hatching = 3.6mm 



Lepidopsetta bilineata 

 egg diameter = 1.02-1. 09mm 

 NL at hatching = 3.9mm 



Isopsetta isolepis 

 egg diameter = 0.90-0. 99mm 

 NL at hatching = 2.9mm 



Pertseva-Ostroumova 1961 



Richardson et al 1980 



Fig. 8. Newly hatched yolk-sac larvae of related fishes with pelagic and demersal eggs of comparable sizes. 



tionally, such as a particular type of nourishment or locomotion. 

 Also the endpoints for the stages should be easily observed and 

 sharply defined. 



The most general scheme of terminology of early development 

 of fishes includes (Fig. 5): 



The "egg stage" (spawning to hatching). The egg stage is used 

 in preference to the embryonic stage because there are characters 

 present during this stage other than just embryonic characters 

 (e.g., those associated with the egg envelope). 



The "larval stage" (hatching to attainment of complete fin 

 ray counts and beginning of squamation). One of the funda- 

 mental events in development of most fishes is the flexion of 

 the notochord that accompanies the hypochordal development 

 of the homocercal caudal fin. It is convenient to divide the larval 

 stage on the basis of this feature into "preflexion." "flexion," 

 and "postflexion" stages. The flexion stage in many fishes is 

 accompanied by rapid development of fin rays, change in body 

 shape, change in locomotive ability, and feeding techniques. 



The "juvenile stage" (completion of fin ray counts and be- 

 ginning of squamation until fish enters adult population or at- 

 tains sexual maturity). 



Transitional stages can also be recognized: the "yolk-sac larval 

 stage" (between hatching and yolk-sac absorption); and the 

 "transformation stage" (between larva and juvenile). Meta- 

 morphosis occurs during this stage and is considered complete 

 when the fish assumes the general features of the juvenile. 



The life histories of some fishes include other specialized 

 ontogenetic stages that have received various names. In some 

 cases, these are the generic names under which these stages were 



described before they were recognized as larvae of other species 

 (e.g., the leptocephalus stage of Anguilliformes, the scutatus 

 stage of Anlennarius. the vexillifer stage of Carapidae. and the 

 kasidoron stage of Gihhertchthys). In other cases, consistent fea- 

 tures of development of a group permit useful subdivisions of 

 stages (e.g.. in leptocephali the engyodontic and euryodontic 

 stages). 



The Egg Stage 



Hempel (1979) reviewed the egg stage relative to fisheries 

 investigations. Ahlstrom and Moser (1980) presented a concise 

 review of the range of characters observed in pelagic fish eggs, 

 particularly those useful in identifying eggs in plankton samples. 

 Sandknop and Matarese in this volume also discuss this subject 

 in detail. The characters that have proven useful for egg iden- 

 tification include egg size and shape, size of perivitelline space, 

 yolk diameter and character (homogeneous or segmented), num- 

 ber and size of oil globules, texture of the egg envelope (smooth 

 or with protrusions), pigment on the yolk and embryo, and 

 characters of the developing embryo (relative rate of develop- 

 ment of various parts, body shape, number of somites) (Table 

 2). 



The egg stage has been subdivided by a number of workers 

 (e.g., Apstein, 1909). Fishery biologists need to determine the 

 age of eggs at the time of collection for production, drift, and 

 mortality estimates. Embryologists have designated stages to 

 coincide with significant developmental features. While the stages 

 of fishery biologists are designed to divide the embryonic stage 

 into several easily recognized portions, embryologists are more 



