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...fischeri) new species, from the eastern Atlantic, including the Mediterranean Sea and Ascension Island. Adults of all three species are superficially similar with a black blotch on the lower half of the pectoral fin, a black spot on the upper margin of opercle, one or two pairs of enlarged symphyseal canines on the lower jaw, and a similar pattern of breast squamation. Each species has a different pattern of hyperostotic bone development and anal-fin color. The two sympatric eastern Atlantic species also differ from each other in number of dorsal- and anal-fin rays, and in large adults of C. fischeri the lobes of these fins are longer and the body is deeper. Caranx hippos from opposite sides of the Atlantic are virtually indistinguishable externally but differ consistently in the expression of hyperostosis of the first dorsal-fin pterygiophore. The fossil species Caranx carangopsis Steindachner 1859 appears to have been based on composite material of Trachurus sp. and a fourth species of the Caranx hippos complex. Patterns of hyperostotic bone development are compared in the nine (of 15 total) species of Caranx sensu stricto that exhibit hyperostosis.
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Species of the Caranx hippos complex or crevalle jacks (Fig. 1) are fished commercially or recreationally in coastal waters throughout their range. Recognized as "superb light tackle species" by the International Game Fish Association (IGFA, 2006), they are important apex predators in inshore tropical waters--all species attaining maximum sizes approaching or exceeding 22.7 kg (50 lb). They are also commonly exhibited in public aquaria and books on marine fishes usually include accounts of them for the areas where these species are found. Despite this importance, there has been considerable confusion regarding the taxonomy and geographic distributions of these species. Gill and Kemp (2002) discussed the potentially serious implications for fishery and conservation managers of an inadequate taxonomic understanding of putatively widespread shore-fish species. Blaber (2002) noted that one of the major obstacles to ecological research in developing countries is the difficulty associated with correct identification of tropical marine and estuarine fishes, which is exacerbated by an overall decline in funding throughout the world for taxonomic research.
[FIGURE 1 OMITTED]
In a general review of the phenomenon of hyperostosis in fishes, including those of the allopatrically distributed and externally nearly identical species Caranx hippos (Linnaeus) (Atlantic Ocean) and C. caninus Gunther (eastern Pacific Ocean), Smith-Vaniz et al. (1995) determined that patterns of hyperostotic bone development were often species-specific. These findings stimulated us to re-evaluate the taxonomic status of specimens from the eastern Atlantic identified as Caranx hippos, which we herein recognize as actually representing two species. The primary objectives of this research were to describe a new species of West African Caranx that has been routinely misidentified as C. hippos, to provide diagnoses and comparisons for all members of the Caranx hippos complex, and to determine their geographic distributions.
This study has been hampered by the scarcity of preserved adults of Caranx hippos from the eastern Atlantic. This scarcity is not surprising because natural history museums and institutional fish collections do not exist in any coastal West African country, and preservation and shipment of large fish specimens from the region are logistically difficult. Color photographs of Caranx hippos provided by the International Game Fish Association and numerous colleagues indicate that adults of this species are relatively common locally, especially during October to February. We urge fishery biologists and others who have the opportunity to obtain adults of fishes that mature at relatively large sizes to help ensure that at least a few such specimens are available in major research collections.
Taxonomic history
The genus Caranx was established by Lacepede (1801, p. 57) and the type-species Caranx carangua Lacepede was apparently first designated by Desmarest (1856, p. 242) as Caranx carougus [sic] Bloch, which is a junior synonym of Scomber hippos Linnaeus. Two other generic or subgeneric names have been applied to these species (Tricropterus Rafinesque, 1810 and Carangus Girard, 1858), but both are junior synonyms of Caranx because the type species of these nominal taxa is also Scomber carangus Bloch.
Caranx hippos was first described (Linnaeus, 1766) from Carolina as Scomber hippos. The putative holotype, a right half-skin (Wheeler, 1985), was included in one of the last shipments of dried fish specimens sent to Linnaeus by the colonial physician Alexander Garden (Sanders, 1997). Synonyms of Caranx hippos (see species account) are either unnecessary replacement names or Linnaeus's original description was not considered. Nichols (1920), because his superficial description of his new Brazilian subspecies, Caranx hippos tropicus, was based on too few specimens, failed to appreciate the range of variation in the species, and other workers have correctly disregarded this trinominal. In his description of the eastern Pacific Caranx caninus, Gunther (1867, 1868) did not compare this species with any other species. Jordan and Gilbert (1883), Jordan (1895), and Gilbert and Starks (1904) all concluded that this nominal species was indistinguishable from the western Atlantic C. hippos. In their major work on the fishes of Panama, Meek and Hildebrand (1925) also did not recognize C. caninus as a valid species, stating "a careful comparison of our large series from the two coasts discloses no differences of importance." Hildebrand (1946) continued to recognize fish from both oceans as conspecific. Berry (1974) stated that eastern Pacific and western Atlantic specimens of Caranx hippos are essentially identical. Eschmeyer and Herald (1983) stated that C. caninus might not be a valid species. Eschmeyer (1998) and Castro-Aguirre et al. (1999) both treated it as a synonym of C. hippos; however, the former subsequently recognized C. caninus as a valid species (Eschmeyer (1)).
Most recent authors have recognized a single eastern Atlantic member of this species group, which has been uncritically referred to as Caranx hippos (Fowler, 1936; Bini, 1968; Hureau and Tortonese, 1973; Bauchot and Pras, 1980; Smith-Vaniz and Berry, 1981; Smith-Vaniz, 1986; Smith-Vaniz et al., 1990; Bauchot, 1992). In the few cases where two species were recognized (Cadenat, 1960; Blache et al., 1970; Okera, 1978), the scientific names used for both species were misapplied. The name C. carangus Valenciennes [sic] (the account given in Cuvier and Valenciennes, 1833 is not an original description) was used for the true C. hippos and the superficially similar new species (C. fischeri) was routinely misidentified as C. hippos.
Materials and methods
Abbreviations used for institutional depositories and cooperative organizations are as follows: American Museum of Natural History, New York (AMNH); Academy of Natural Sciences of Philadelphia (ANSP); The Natural History Museum, London (BMNH); California Academy of Natural Sciences, San Francisco (CAS, CAS-SU); Food and Agricultural Organization of the United Nations, Rome (FAO); International Game Fish Association, Dania Beach, Florida (IGFA); Institut Royal des Sciences Naturales de Belgique, Brussels (IRSNB); Musee Royal des de l'Afrique Centrale, Tervuren (MRAC); Museum National d'Histoire Naturelle, Paris (MNHN); Naturhistorisches Museum, Wien (Vienna), Austria (NMW); South African Institute of Aquatic Biodiversity (formerly J. L. B. Smith Institute of Ichthyology), Grahamstown (SAIAB); Scripps Institution of Oceanography, La Jolla (SIO); Florida Museum of Natural History, Gainesville (UF); National Museum of Natural History, Washington, D. C. (USNM); Universitat Hamburg (ISH, ZMH); Zoological Museum, University of Copenhagen (ZMUC).
Parenthetical expressions in material examined include number of specimens, if more than one, followed by the size range in millimeters fork length (FL); cleared and stained specimens are indicated as "C&S." Localities are abbreviated and listed only by major geographic areas for Caranx caninus and western Atlantic C. hippos. Except for those given in the scatter plots, measurements are of limited value in distinguishing members of the hippos complex (and then only for specimens >200 mm FL). Total lengths (TL) are given when that was the only length measurement reported in cited references. All measurements are in mm unless specified as cm. Measurements expressed in percent fork length or head length, are given only in the description of the new species Caranx fischeri. Fork length is measured from the front of the upper lip to the tip of shortest median caudal-fin ray. Body depths are measured from the anterior base of the spinous dorsal fin (D10) to the origin of the pelvic fin (P20) and from the anterior base of the spine at the origin of the dorsal-fin lobe (D20) to the anterior base of the anal-fin spine at the origin of the anal-fin lobe (A20). Lengths of the dorsal- (D2) and anal-fin (A2) bases are straight-line measurements from either the D20 or A20 to the posterior base of the terminal fin ray of the respective fin. Head length is measured from the front of the upper lip to the posterior end of the opercular flap. Snout length is measured from the anterior end of the upper lip to the anterior edge of the eye. Eye diameter is the greatest bony diameter. Upper jaw length is taken from the anterior end of the upper lip to the posterior end of the maxilla. The curved part of the lateral line is measured as a chord (straight-line distance) of the arch extending from the upper edge of the opercle to its junction with the straight part; the straight part of the lateral line is measured from its junction with the curved part to its termination on the caudal-fin base (end of last scute). Scutes are defined as scales that have a raised horizontal ridge or a small to moderate projecting spine on the posterior margin ending in a point not exceeding a 120[degrees] angle; for detailed description and illustrations of scute formation and development in Caranx crysos (Mitchill) see Berry (1960). All scutes were counted, including those extending onto the caudal-fin base. Pectoral-fin ray counts do not include the dorsal-most spine-like element. Gill raker counts are from the first gill arch (usually on the right side), and the raker at the angle is included in the lower-limb count; rudimentary gill rakers, with the diameter of their bases greater than their height, are defined as tubercles or short rakers. The anterior dorsal-fin pterygiophore formula indicates the interdigitation pattern of supraneurals and pterygiophores within interneural spaces; neural spines are indicated by slashes, supraneural (predorsal) bones by an "S," pterygiophores by "2" (pterygiophores with two supernumerary rays and a serially associated ray) or "1" (no supernumerary ray and one serially associated ray).
Results
Taxonomy and distributions
Some recent authors (Amezcua-Linares, 1996; Randall, 1996; McBride and McKown, 2000) still follow Briggs (1960) in erroneously reporting a worldwide distribution in tropical and subtropical latitudes for Caranx hippos, although Nichols (1920) had correctly concluded that records of the species from the Indian and western Pacific oceans were based on misidentifications. Other authors (Talwar and Kacker, 1984; Krishnan and Mishra, 1994; Mishra et al., 1999; Khan, 2003; Mishra and Krishnan, 2003) reported C. hippos as C. carangus (Bloch) from the Indian Ocean based on misidentifications of Caranx heberi (Bennett). What was once considered to be a single widespread species is herein recognized as consisting of three species (Fig. 2). For almost a century, most ichthyologists and fishery biologists who have worked on West African crevalle jacks have failed to distinguish the new species Caranx fischeri described herein from C. hippos, although both species are commonly taken together.
[FIGURE 2 OMITTED]
Adults of Caranx hippos from opposite sides of the Atlantic Ocean are indistinguishable externally but exhibit consistent differences in the degree of development of the hyperostosis in the first dorsal-fin pterygiophore and neural spines of some of the anterior vertebrae (see "Geographic variation" in C. hippos species account). Although we consider these predictable ontogenetic and consistent site-specific patterns obvious evidence of genetic divergence associated with bone metabolism, an important consideration is the unknown functional significance of hyperostosis. In light of this, we believe it would be premature to recognize the eastern Atlantic population of C. hippos as taxonomically distinct. No formal change in classification should be made in the absence of collaborative molecular data.
The Caranx hippos complex
The C. hippos species complex can be diagnosed by the following combination of characters: a pair of strong symphyseal dentary canines (Fig. 3); breast naked ventrally except for a small oblong patch of prepelvic scales (Fig. 4) which forms at about 30 mm FL; rounded black blotch on the lower rays of the pectoral fin in adults; large black opercular spot; and vertebrae 10 precaudal + 14 caudal. Only the black blotch on the pectoral fin is unique to these species. Adults of the horse-eye jack, Caranx latus Agassiz, occasionally have a somewhat similarly placed dusky blotch on the pectoral fin (although the dark area is different in character and never as well defined as in C. hippos), and this similarity in appearance has occasionally resulted in field misidentifications, especially by scuba divers unfamiliar with both species. The typical breast squamation pattern of the C. hippos species complex is not duplicated in any other Atlantic or eastern Pacific species of Caranx, although it occurs in three Indo-west Pacific species: commonly in C. ignobilis (Forsskal) and C. papuensis Alleyne and Macleay, and less frequently in C. heberi. Dentition has been used as an important diagnostic character of carangid genera, but comparison of the dentition of a large number of carangid species reveals an almost complete continuum of dentition types that in some cases does not agree with traditional generic assignments. In all members of the C. hippos complex the upper jaw has an outer row of strong canines (widely spaced in adults) and an inner band of small villiform teeth that is widest anteriorly. The lower jaw has a single row of strong conical teeth that are smaller anteriorly, and one or two pairs of noticeably enlarged inner symphyseal canines. Enlarged symphyseal dentary canines are absent in the following species of Caranx: C. crysos, C. caballus Gunther, C. melampygus Cuvier, C. papuensis, and C. senegallus Cuvier. Gill (1862) proposed the genus Paratractus for Caranx pisquetus Cuvier, a junior synonym of C. crysos, primarily because of the absence of symphyseal canines.
[FIGURES 3-4 OMITTED]
Some recent authors follow Randall (1996) in assigning several common Atlantic carangids to the genus Carangoides Bleeker, but we maintain traditional usage for reasons given by Smith-Vaniz et al. (1999, p. 237).
Hyperostosis in Caranx species
Hyperostosis appears to have been an integral part of the evolutionary history of the Caranx hippos complex, but the pattern of expression is surprisingly different in each species (Table 1). Hyperostosis involves the expansion or swelling of certain bones into globose, gall-like structures characterized by cellular bone foci and bone-resorbing osteoclasts.
In most carangids the condition is usually apparent only in relatively large individuals (but can be detected histologically in smaller individuals) and the onset in different bone foci is typically sequential rather than simultaneous. A large number and size range of individuals of each species usually must be examined before the...
NOTE: All illustrations and photos
have been removed from this article.
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