HORN: STROMATEOIDEI 



Table 162. Extended. 



623 



X 



X 



X 



Behavioral and morphological features of young stromateoids 

 are potentially informative as taxonomic characters. Certain 

 ones of these traits appear to be related to the widespread as- 

 sociation of these fishes with a variety of floating objects in the 

 ocean. In general, loss of the swimbladder accompanies allo- 

 metric growth in pectoral fin length and changes in pigmentation 

 pattern as part of the transition from the juvenile to the adult 

 stage (Horn, 1975). Stromateoid fishes associated with floating 

 objects usually have conspicuous blotches or bands of pigment 

 on their bodies as juveniles then become more uniformly pig- 

 mented as deeper-living, presumably independent and contin- 

 uously swimming adult fish. Haedrich (1967) proposed that 

 banding is protective coloration for the fishes during the period 

 when they live in the shifting shadows beneath jelly fishes. There 

 are exceptions to this apparent relationship between pigmen- 

 tation and behavior. For example, juveniles of Ariomma are 

 banded yet appear to seldom associate with floating objects 

 whereas young Telragonurus are uniformly pigmented but, as 

 Janssen and Harbison (1981) observed, associate intimately with 

 salps and pyrosomes. The re?ra^o«Mn/5-salp/pyrosome asso- 

 ciation, however, is different in that the fish are inside rather 

 than beneath the floating objects. Pigmentation pattern and type 

 of association are the two ontogenetic characters used in the 

 phylogenetic analysis (see below). 



Fin characters. — Meristic characters (Table 1 62) have been used 

 widely to distinguish stromateoid taxa especially at the species 

 level (e.g., Haedrich, 1967; Haedrich and Horn, 1972; Horn, 

 1970b, 1973; Horn and Haedrich, 1973; Ahlstrom et al., 1976; 

 Butler, 1979; McDowall, 1982). As in most other perciform 

 fishes, the pelvic fin (I, 5) and caudal fin (17 principal rays, 15 

 branched) of stromateoids have stabilized counts (the pelvic fin, 

 however, is absent in three stromateoid genera). The number 

 of secondary caudal rays, although exhibiting intraspecific vari- 

 ation, can be an important taxonomic character among species 

 within a genus (Ahlstrom et al., 1976). The dorsal fin of stro- 

 mateoids may be continuous or divided into two fins. This trait 

 is used as a generic character in the present paper (Tables 164, 

 1 65). It is not always possible to distinguish between spines and 

 rays in those species with a continuous dorsal fin (see Table 

 162). The complement of anal fin rays in stromateoids is pre- 

 ceded by to 7 anal spines with most species having 2 or 3 

 spines. The number of pectoral fin rays varies from 14 to 27 



among stromateoids, but the overlap among species limits its 

 use as a taxonomic character. 



Two different sequences of fin formation occur in oceanic 

 stromateoids depending primarily on whether the pelvic fins 

 form early (before the other fins) or whether they form late. 

 Ahlstrom et al. (1976) found that the pelvics are first to form 

 in Amarsipus, Psenes and probably also Nomeus whereas they 

 are last to form in Cubiceps, Icichthys and Telragonurus. Fahay 

 (1983) reported that the pelvics are also last to form in Centro- 

 lophus. These ontogenetic patterns have potential significance 

 as taxonomic characters; however, they must be described for 

 other genera before they can contribute to an understanding of 

 stromateoid relationships. 



Morphometries. — SXrom?i\eo\ds vary substantially in their mor- 

 phologies, especially body depth, but show no abrupt meta- 

 morphic changes in the transition from the larval to the juvenile 

 to the adult stage. Allometric growth is common in these fishes 

 and complicates the use of morphometries as taxonomic char- 

 acters. Taxa at similar stages of development must be compared 

 if morphometric characters are to have validity. Ahlstrom et al. 

 (1976) used morphometries in distinguishing among species in 

 genera such as Schedophilus and Psenes. Because of allometry 

 and the less than complete information on different develop- 

 ment stages of several genera, morphometric characters were 

 not used in the phylogenetic analysis of stromateoid genera (see 

 below). 



Skeletal characters. — M\\s,Xrom et al. (1976) in their study of 

 the early life history stages of oceanic stromateoids found the 

 following skeletal characters to be of particular relevance: (1) 

 total number of vertebrae, (2) co-occurrence of a pair of pleural 

 ribs and a haemal spine on each of one or more caudal vertebrae, 



(3) separation of vertebrae into precaudal and caudal groups, 



(4) position of anal fin pterygiophores in relation to haemal 

 spines, (5) number and position of dorsal fin pterygiophores and 

 predorsal bones in relation to neural spines, and, (6) the number 

 of supporting bones of the caudal fin. While not strictly onto- 

 genetic in nature, these characters are most readily discerned 

 from examiniation of cleared and stained larvae and early ju- 

 veniles. 



Of the above characters, only the number of predorsal bones 

 and the number of hypurals were used in the phylogenetic anal- 



