142 



ONTOGENY AND SYSTEMATICS OF FISHES -AHLSTROM SYMPOSIUM 



form is basically that of the adult. Guts are simple with no 

 elaborations in all species. At hatching Umbra has a shorter gut 

 and fewer myomeres than Esox and this is reflected in there 

 being 5 myomeres between the yolk sac and the anus in newly 

 hatching U. pygmaea and 12 in E. americanus (Malloy and 

 Martin, 1982). 



Relationships 



Malloy and Martin (1982) point out three ontogenetic char- 

 acteristics shared by Esox and Umbra, which indicate close 

 relationship. The position of the heart at the time of formation 

 is on the yolk sac anterior to and left of the head. All other fish 

 for which position of the forming heart is noted have it forming 

 under the head in the pericardial cavity or, as in the Atherini- 

 formes, near the midline and anterior to the head. The yolk-sac 

 circulatory pattern consists of paired simple common cardinals, 

 a posterior rete formed by the subintestinal vitelline vein and 

 paired or single hepatic vitelline veins which enter the rete before 

 the subintestinal vitelline vein joins the common cardinals at 

 the heart (see Fig. 74). This differs from all other salmoniform 

 fish for which the pattern is described (Kunz, 1 964; Soin, 1 966). 

 The oil droplets go through a predictable series of clustering and 

 dispersion. Oil droplet movement of this sort has only been 

 documented previously by Ahlslrom ( 1 968) for bathylagid smelts 

 of the genera Bathylagus and Leuroglossus. 



McDowall (1969) recognized a salmonoid-osmeroid-esocoid 

 lineage but states "Where esocoids fit into this series of sub- 

 orders and families is not clear to me." Rosen (1973) likewise 



considers the esocoids and salmonoids to probably be closely 

 related but considers this alignment to be provisional. Fink and 

 Weitzman (1982), in contrast, state that they find no evidence 

 to consider the esocoids closely related to the other Protacan- 

 thopterygii (sensii Rosen, 1 974), which are the Agentinoidei and 

 Salmonoidei (including the Salmonoidea plus Osmeroidea). 

 Fink and Weitzman list the esocoids as sedis mutahilis at the 

 euteleostean level or as the sister group to all other euteleosts. 

 Soin (1980), on the basis of egg development patterns, feels that 

 the esocoid fish are incorrectly placed as a suborder of the Sal- 

 moniformes, however he gives no guidance as to correct place- 

 ment. While the ontogenetic evidence presented in Table 30 is 

 not conclusive it suggests that there is a large difference between 

 the esocoids and the Salmonoidei and this is consistent with the 

 opinions of Fink and Weitzman. 



The vertebrae of Umbrids have a pronounced anterior con- 

 striction, giving them an asymmetrical appearance, however 

 Novumbra and Dallia show this characteristic only while young 

 and most noticeably in the mid-abdominal region. In Esox the 

 vertebrae are either unconstricted or are constricted both an- 

 teriorly and posteriorly so that they appear symmetrical (Cav- 

 ender, 1969). Other differences between the Esocidae and the 

 Umbridae are seen in the Umbridae having nine or fewer bran- 

 chiostegals, fewer infraorbitals, no supratemporals or intercalars 

 and usually fewer than 41 vertebrae (Wilson and Veilleux, 1982). 



Chesapeake Biological Laboratory, University of 

 Maryland, Box 38, Solomons, Maryland 20688. 



Salmonidae: Development and Relationships 

 A. W. Kendall, Jr. and R. J. Behnke 



SALMONIDS (whitefishes, ciscoes, grayling, trout, and salm- 

 on) are highly important in terms of aesthetic appreciation, 

 commercial and recreational value, and scientific study. Studies 

 of the development of salmonids from hatching until the time 

 of yolk depletion, and of the relationships among subfamilies 

 and genera have been largely neglected [see review of systematics 

 by Dorofeyeva et al. (1980)] despite the large body of literature 

 on early embryological development and relationships among 

 species and populations. Salmonids all spawn in fresh or brack- 

 ish water, some are anadromous while others are strictly fresh- 

 water. The family is composed of about 10 genera in three 

 subfamilies: Coregoninae, Thymallinae, and Salmoninae (Table 

 32) (Nelson, 1976). 



Along with a precise homing ability, salmonids tend to form 

 genetically isolated populations. They seem to be able to occupy 

 new niches and habitats as these become available in the cold 

 temperate parts of the Northern Hemisphere. One result of this 

 adaptability is the existence of taxonomic problems mainly at 

 the species-population levels (Utter, 1981). 



Development 



Post-hatching development of salmonids has been little stud- 

 ied (Table 33), and only a superficial analysis of comparative 

 developmental stages has been attempted (Soin, 1980). Thy- 

 mallus and the salmonines share apparently advanced features 

 of development such as large yolk sac with an extensive vitelline 

 circulatory system and development of rather uniform intense 

 pigment, while coregonines develop larvae that are more typical 

 of other freshwater fishes (Faber, 1970). Thymallus seems inter- 

 mediate between the coregonines with a "normal" larval stage 

 and the salmonines in which the larval stage is largely bypassed 

 (the young have fully formed fins by the time the yolk is ab- 

 sorbed). Parr marks (vertical blotches or bars of pigment over 

 the trunk of juveniles) are present in all salmonids except Cor- 

 egomts a.nd StenodushuX are not seen injuveniles of other fishes. 

 Norden (1961) incorrectly considered the early stages of Core- 

 goniis artedii as figured by Fish (1932) to be similar to those of 

 Thymallus arclicus. He also stated that "the development of 



