Symphysanodon

Symphysanodon spp.

We have identified 26 specimens (10-119 mm SL) only to the genus Symphysanodon; data for them are: 13°07’ S, 119°02’ W (SIO 96-35; 25 mm SL); French Polynesia (BPBM 31670; 53 mm SL.-BPBM 37131; 54 mm SL.-GMBL 69-30; 35 mm SL.-GMBL 85-99; 57 mm SL); Hawaiian Islands (BPBM 24864; 52 mm SL.- BPBM 28856; 77 mm SL); Johnston Atoll (BPBM 29266; 4 [of 5, fifth identified as S. maunaloae]: 46-49 mm SL); Vanuatu, NE of Espíritu Santo Island (GMBL 66-13; 2: 10- 19 mm SL); New Caledonia (GMBL 56-15; 6: ca. 40->51 mm SL); South Pacific (presumably, actual locality of capture not known; GMBL 72-404; 37 mm SL); Papua New Guinea, Gulf of Papua (GMBL 71-238; 59 mm SL.-GMBL 71-239; 53 mm SL); Guam (GMBL 68-62; 119 mm SL); Somalia, Gulf of Aden (USNM 326398; 3: 40-47 mm SL; see above under S. andersoni). Most of the specimens (17) listed above were captured by midwater trawls or nekton net or were removed from the stomachs of other fishes (i.e., species of Epinephelus, Seriola, Etelis, Thunnus). While at the MNHN in October 2003, G. David Johnson identified an additional specimen collected off New Caledonia (St. Vincent) as a Symphysanodon (MNHN 1990-1473, 44 mm SL).

The larvae of Symphysanodon are quite distinctive, being “unique in their possession of hornlike frontal spines” (Johnson, 1984: 464, fig. 254A). Leis and Trnski (1989: 228- 231, fig. 51; 2000: 394-398, fig. 100) described and illustrated larvae of Symphysanodon based on material collected in the Indo-Pacific and wrote (1989: 228; 2000: 394): “The remarkable head spination is extensive. The most obvious features are the massive, paired, serrate frontal and preopercular-angle spines.” In fact, frontal spines or their remnants are frequently present on fairly large individuals. Consequently, even small specimens are relatively easy to identify to genus but often difficult to place in a species with confidence. Konishi (1988) provided descriptions and illustrations of 3.8 and 10.5 mm larvae of Symphysanodon that were identified as S. katayamai (see above under S.katayamai). The specimens illustrated by Konishi (1988) show the extremely well-developed head spination noted by other authors. There are many pelagic larval and postlarval specimens of Symphysanodon obtained from numerous localities in the western North Atlantic, mainly by midwater trawls, in the collections of the Museum of Comparative Zoology (pers. comm., Karsten Hartel, 13 October 1999); those localities are plotted in Figure 16.

Fourmanoir (1969) and Kami (1971) listed specimens, identified as S. typus, taken from the stomachs of predatory fishes (Alepisaurus ferox [Alepisauridae] caught in the southwest Pacific and Seriola sp. [Carangidae] taken off Guam, respectively), but provided no information that would allow verification of their identifications. Fourmanoir (1976) noted 10 specimens (18-30 mm, presumably SL), apparently postlarvae, identified as Symphysanodon sp., collected by “pelagic trawl” in the southwest Pacific, and Uchida and Tagami (1984) included Symphysanodon sp., S. typus, and S. maunaloae in their table 5, a list of fishes caught on the Townsend Cromwell northwest of the Hawaiian Archipelago by trawling over Hancock and other seamounts, but gave nothing that would substantiate the use of those names. Richards (1984) reported larvae of Symphosanodon [sic] spp. collected in the Caribbean Sea by bongo nets in the summer of 1972 and winter of 1973.

Gloerfelt-Tarp and Kailola (1984:172-173) provided a photograph of a specimen and description of material identified as Symphysanodon sp., describing the coloration as: “Dusky red, darker above. Fins rosy, outer dorsal, caudal and ventral fins greenish.” Further along those authors related: “First ray of ventral fin produced into a long, trailing filament; both caudal fin lobes produced into long filaments.” The fish in the photograph labeled Symphysanodon sp. (p. 172) has the pelvic fin and upper lobe of the caudal fin well produced. Other data presented by Gloerfelt-Tarp and Kailola (1984: 173) are: “Body depth 3.8-3.9 in SL.... D IX, 9. A III, 7. Total GR 34. L. lat. 52-53. (voucher: 75 mm SL).” The counts of lateral -line scales fall within the range of those for S. typus but outside the range for S. maunaloae; however, the count of total gillrakers is lower than the lowest count recorded for S. typus, falling within the range of counts for S. maunaloae. Some specimens (presumably males) of S. maunaloae have well-produced pelvic fins and caudal-fin lobes, as do the above described specimens, but so far as is known the pelvic and caudal fins are not extensively produced in S. typus. Unfortunately the repository for the voucher specimen was not given, and as a consequence we can offer nothing on the species identification of this material.

In late November 2004, Richard Pyle observed numerous individuals of an unidentified species of Symphysanodon during two deep dives (ca. 120 m) off the southwest side of Gau Island, Fiji (lat. 18.05° S, long. 179.3° E). He took a number of photographs of that species and related (to VGS, in litt. 7 December 2004) that all of the individuals that he saw were “about 150 mm SL, purplish pink dorsally fading to pale pink ventrally.... Dorsal fin translucent yellow... caudal fin with distinct white tips.... Unlike the Symphysanodon that I have seen in Hawaii and elsewhere, this fish did not retreat by swimming through mid-water; rather, they would descend to the reef and hover in front of a hole, then disappear into the hole when approached too closely.” In a subsequent e-mail transmission (9 December 2004), Pyle reported that a video shows that this species has filamentous caudal-fin lobes and pelvic fins.

Locality data for specimens of Symphysanodon identified only to genus are plotted in Figures 16 and 17.

Osteological characters

In most specimens of all species of Symphysanodon, except S. octoactinus, the formula for configuration of supraneural bones, anterior neural spines, and anterior dorsal pterygiophores is 0/0/0 + 2 + 1/1/1/. Symphysanodon octoactinus has a different configuration, i.e., 0/0/0 + 2/1 + 1/1/. Other configurations observed are: 0/0/0 + 2 + 1/1 + 1//1/ in one specimen of S. berryi, 0/0 + 0/2 + 1/1/ 1/ in one of S. katayamai and two of S. maunaloae, 0/0 + 0 + 2/1/1/ in one of S. maunaloae, and 0/0/2 + 1/1/1/ in one of S. maunaloae. See Table 8 for a summary by species of the configurations encountered.

Radiographs show that four of the species of Symphysanodon (S. andersoni -one specimen examined, S. katayamai -four, S. typus -17, Symphysanodon sp. from the Comoros -one) and the Symphysanodon sp. from the Gulf of Aden (three) have parapophyses on the first caudal vertebra (i.e., the eleventh vertebra) and that six species (S. berryi -44, S. maunaloae -33, S. mona -one, S. octoactinus -14, S. parini -10, S. rhax - six) lack those processes. In those species having parapophyses on the first caudal vertebra the haemal spine of that vertebra is displaced posteriorly as compared with its position in the other species.

We recorded data on hypural bones from examination of radiographs of 106 specimens, representing all of the previously described species of Symphysanodon and the three new species, and, at our request, G. David Johnson studied a radiograph of the two specimens of Symphysanodon removed from the CAS Latimeria (CAS 33111) collected in the Comoros (McCosker, 1979). Unfortunately, the resolution on some radiographs makes it difficult to determine the extent of hypural fusions in a number of specimens. The parhypural and hypural five were found to be autogenous in all specimens in which they could be clearly seen, but considerable variation was observed among the species in fusions of the other hypural bones -from none in one species to partial in some specimens of other species to what may be complete fusion at first appearance in early development in other specimens. Data on hypural fusions (hypural one with two and hypural three with four) are summarized in Table 9. (In that table, partial fusions are considered as fusions.) Symphysanodon octoactinus is unique (in the genus), at least over the size range (60-115 mm SL) of the specimens examined, in having hypurals three and four autogenous, and S. katayamai and S. typus are distinctive in having relatively small specimens (<75mm SL) with hypurals one and two represented by a single plate. In S. andersoni only a single large specimen (157 mm SL) was available for radiography; consequently, the fusion of hypurals one and two displayed by it may be ontogenetic and not representative of the complete size range of the species. In summary, it seems that phylogenetic fusions of hypural bones have occurred in the genus and that ontogenetic fusions may occur in some of the species.

In Symphysanodon, configurations of supraneural bones, anterior neural spines, and anterior dorsal pterygiophores, presence or absence of parapophyses on the first caudal vertebra, and presence or absence of hypural fusions may be useful in identification, particularly of small specimens, and may be helpful in determining relationships among the species.

Sexuality

William A. Roumillat examined histological sections of the gonads of specimens of three species of Symphysanodon (parini -10 specimens, berryi -three, and rhax -two) and found all of those individuals to be gonochoristic.

Relationships

Symphysanodon octoactinus is the most distinctive of the species of Symphysanodon, possessing a configuration of the supraneural bones, etc. (see Table 8) and a hypural morphology(see Table 9) that are unique within the genus. In addition, S. octoactinus usually has eight segmented rays in the anal fin (>90 % of specimens), whereas the other species almost always have seven, never eight. Symphysanodon mona has a gill arch morphology that is unlike that observed in the other species (gill arches of all species of Symphysanodon have been examined except S. andersoni and the species from the Comoros). Four of the species (S. andersoni, S. katayamai, S. typus, the species from the Comoros) possess parapophyses on the first caudal vertebra and the same type of hypural morphology (one of the two specimens from the Comoros differs; see Table 9), characters distinguishing them from other members of the genus. Symphysanodon maunaloae and S. parini are morphologically extremely similar, and based on available information it seems that they may be sister species. The same can be said for S. berryi and S. rhax. However, given that there are probably undescribed species of Symphysanodon yet to be collected, present in museums in unsorted collections, or represented by larvae or badly damaged specimens, it is premature to comment further on relationships.

Geographic distribution

Localities of capture are plotted in Figures 4, 9, 16, and 17. Many plotted localities are for specimens that we did not examine. Some points are based on literature reports that we consider reliable; others (mostly for larvae and postlarvae), on records from museum collections. As noted above, the larvae of Symphysanodon are quite distinctive. Consequently, even small specimens are relatively easy to identify to genus. Localities from museum records are included only for those specimens for which we could evaluate the quality of the identifications -either by knowing who made the determinations or by asking ichthyologists at the museums to check identifications. Many of the habitats, including rocky slopes, in which species of Symphysanodon dwell are difficult to sample using dredges and trawls because those fishing gears frequently snag and are damaged or lost. Difficulty in collecting no doubt introduces an artifactual element of unknown degree into explanations of the distribution of these fishes.

Benthic stages (pre-adults, adults) of Symphysanodon species are mainly associated with moderately deep waters over rocky or coral-reef habitats in the vicinity of oceanic islands between latitudes 25° N and 25° S. Pelagic stages (larvae, post-larvae, pre-juveniles) appear to be similarly restricted, except in the western Atlantic (Figure 16). In that area, where considerable mid-water and plankton collections have been made, pelagic stages occur well north of 25° N, apparently transported by the Gulf Stream. Small, identifiable pelagic stages of S. berryi taken in the middle and southern Gulf of Mexico (Figure 4), where no adults have been reported, are probably waifs brought in from the south by the Caribbean Current. Specimens of S. berryi collected northeast of Bermuda, where the genus is unreported, are juveniles taken pelagically in trawls over deep water, and may be waifs from breeding populations on the deep slopes of Bermuda, which have been little sampled ichthyologically (W. F. Smith-Vaniz, pers. comm.).

The restricted distribution of Symphysanodon mona, known from a single specimen collected with a specimen of S. berryi, is probably a collecting artifact. Absences of Symphysanodon from the continental coasts of the southwestern Atlantic, eastern Atlantic, and eastern Pacific, most of the mainland coast of Asia (China west to the Persian Gulf), and much of the Indian Ocean (particularly the northwestern coast of Australia) probably reflect lack of suitable habitat. Such is not true of the western Indian Ocean island groups (Chagos, Mascarenes, etc.), where dearth of records may result from lack of slope collections. Absences of Symphysanodon from the continental coasts of the southwestern Atlantic, eastern Atlantic, and eastern Pacific do not appear to be collecting artifacts, as there has been considerable trawling in those areas. Absence from the continental coast of the eastern Pacific is duplicated bywarm-water coastally restricted pelagic forms such as Rachycentron (Springer, 1982:fig. 35) and Sphyraena barracuda (Springer, 1982:96; however, cool-temperate species of Sphyraena do occur in the eastern Pacific). A more general historical explanation is probably called for but is presently lacking. Symphysanodon may have been more continuously distributed in the past with former populations becoming extinct in the major areas where they are currently absent.

Molecular comparisons of specimens of S. berryi from the central and eastern South Atlantic islands with specimens of their geographically nearest conspecifics from the southern Lesser Antilles would be of interest in determining degree and age of divergence of those populations. We suspect that the insular central and eastern South Atlantic specimens of S. berryi, although just slightly differentiated morphologically (showing only minor morphometric differences) from Caribbean conspecifics, are probably well differentiated and represent one or two species distinct from S. berryi. Muss et al. (2001) found that populations of the blenniid genus Ophioblennius from the western, central, and eastern Atlantic, which Springer (1962), based on morphology, identified as a single species, apparently represent several species, which they refrained from describing. (Carole C. Baldwin has a manuscript in preparation describing those species, which she has been able to differentiate morphologically based on many more specimens than were available to Springer.) Also, Moura and Castro (2002) have shown that populations of the tetraodontid genus Canthigaster from the western, central, and eastern Atlantic, usually considered as a single species, actually constitute a complex of six species.

Symphysanodon maunaloae is widely distributed in the Pacific (Figure 9). Some of the widely scattered and morphologically variable populations now considered conspecific with S. maunaloae may be recognized eventually at the specific level. Some of the variability(lengths of pelvic fin and caudal-fin lobes) shown by that species is apparently related to sexual dimorphism; some of the other differences are probably the result of allometric growth. In Tables 10 and 11, the geographic variation displayed by S. maunaloae in two characters, depth of body and total number of gillrakers on the first gill arch, is shown.

Conclusion

A reassessment of examined specimens and study of new material will likely lead to the discovery of additional species of Symphysanodon. There may be one or two undescribed species occurring off the islands of the central and eastern South Atlantic that are considered herein as populations of S. berryi, and S. maunaloae may be a species complex (see above under Geographic distribution). As noted by Gill and Kemp (2002) for widely distributed Indo-Pacific shore fishes (see above under Symphysanodon rhax), it seems that the diversity of shelf, slope, insular, and seamount fishes is presently underestimated.