Esocoidei: Development and Relationships 

 F. D. Martin 



THE Esocoidei consist of two families, Esocidae and Um- 

 bridae, with one and three genera respectively (Nelson, 

 1976). Table 30 lists all currently accepted species and gives 

 their geographic ranges. All recent classifications consider the 

 esocoids as members of the Salmoniformes (Greenwood et al., 

 1966; Gosline, 1971; Rosen, 1974; Nelson, 1976; and others). 

 All esocoid fishes live in freshwater and occur in temperate and 

 arctic waters of the Northern Hemisphere. All species are pred- 

 atory with Esox being primarily piscivorous. They are distin- 

 guished from other salmoniform fishes by the lack of the meso- 

 coracoid, lack of pyloric caeca, a single rudimentary arch over 

 PUl, and a single uroneural (Rosen, 1974). Table 31 gives de- 

 velopmental features that characterize esocoid fishes and con- 

 trasts them with Salmonidae and Osmeridae. 



Development 



Eggs are demersal and adhesive in most species (Breder and 

 Rosen, 1966) but Esox niger eggs become buoyant at later stages 

 of development and are not adhesive after water hardening (Jones 

 et al., 1978). Eggs are of moderate size (1.0 to 2.2 mm usually) 

 (Jones et al., 1978) and are either scattered as by Esox or are 

 in nests as with Umbra and Novumhra (Breder and Rosen, 1 966). 



Table 30. 



Genera and Species of Esocoid Fishes and Geograph- 

 ical Ranges. 



Esocidae 

 Esox 

 E. lucius 

 E. reicherli 

 E. masquinongy 



E. niger 



E. americanus 



Umbridae 



Novumhra 

 N. hiibbsi 



Umbra 

 v. krameri 



V. linu 



U. pygmaea 



Datlia 



D. pectoralis 



D. asmirabilis 



Holarctic (Grossman in Lee et al.. 1980). 

 Amur River region of Siberia (Berg, 1948). 

 Eastern North America, primarily Great 



Lakes and Upper Mississippi drainage 



(Grossman m Lee et al., 1980). 

 East Goast drainage of North America, also 



lower Mississippi drainage (Grossman in 



Leeet al., 1980). 

 Eastern half of North America (Grossman m 



Leeetal., 1980). 



Olympic Peninsula of Washington State 

 (Meldnm m Lee el al., 1980). 



Middle and lower Danube System and lower 



Dniester River (Berg, 1948). 

 Southern Ganada and Gentral United States 



(Gilbert m Leeetal., 1980). 

 Southeastern New York to Northern Florida. 



mostly on Goastal Plain (Gilbert in Lee et 



al., 1980). 



Arctic and sub-Arctic Alaska and eastern tip 

 of Sibena (Rohde in Lee et al., 1980). 



Amguema River basin of Siberia (Gheresh- 

 nev and Balushkin, 1980). 



Multiple oil droplets occur with a unique set of movements 

 producing alternating clustering and dispersion as ontogeny pro- 

 ceeds (Malloy and Martin, 1982). 



Larvae of nearly all species are known, and developmental 

 series have been described and illustrated. Figs. 72 and 73 show 

 representative larvae oi Esox and Umbra. Those described hatch 

 relatively undeveloped, with head flexed over and attached to 

 the large yolk sac; the eyes are unpigmented. In all species the 

 notochord is stout and reaches nearly to the margin of the caudal 

 finfold. During flexion the notochord extends well beyond the 

 developing hypurals and may form a separate lobe to the de- 

 veloping caudal fin until the hypurals are complete. In Umbra 

 and Esox the pectoral fin is the first to begin differentiation (but 

 not form rays) with the pelvic fin the last to develop fin rays. 

 All median fins differentiate more or less simultaneously with 

 caudal starting ditTerentiation slightly ahead of the others. 

 Changes in body form are gradual with no noticable point of 

 metamorphosis. Before fin differentiation is complete the body 



Fig. 72. Development of Esox niger from hatching to juvenile. 

 Lengths arc total lengths. (From Mansueti and Hardy, 1967.) 



140 



